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Qaytarilish / Oksidlanish reaktsiyalari - Meri va Kaydon - Biologiya

Qaytarilish / Oksidlanish reaktsiyalari - Meri va Kaydon - Biologiya



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Qaytarilish-oksidlanish reaksiyalari

Umumiy biologiyada ko'pchilik qaytarilish/oksidlanish reaksiyalari (qaytarilish-qaytarilish) Biz muhokama qiladigan metabolik yo'llarda sodir bo'ladi (bog'langan biokimyoviy reaktsiyalar to'plami). Bu erda hujayra o'zi iste'mol qiladigan birikmalarni kichikroq qismlarga ajratadi va keyin bu va boshqa molekulalarni kattaroq makromolekullarga qayta yig'adi. Shu sabablarga ko'ra, biologiyada redoks reaktsiyalarini hech bo'lmaganda intuitiv tushunish va baholashni rivojlantirish muhimdir.

Ko'pchilik biologiya talabalari kimyo kurslarida qaytarilish va oksidlanish reaktsiyalarini ham o'rganadilar; bu turdagi reaksiyalar biologiyadan ham muhim ahamiyatga ega. Talabalar ushbu kontseptsiya bilan tanishish tartibidan qat'i nazar (birinchi navbatda kimyo yoki biologiya), ko'pchilik kimyo va biologiyada juda boshqacha tarzda taqdim etilgan mavzuni topadi. Bu chalkash bo'lishi mumkin.

Kimyogarlar ko'pincha oksidlanish darajasi tushunchasidan foydalangan holda oksidlanish va qaytarilish tushunchalarini kiritadilar. Qo'shimcha ma'lumot olish uchun ushbu havolaga qarang: . Kimyogarlar odatda talabalardan kimyoviy reaksiyada ishtirok etayotgan molekulalardagi alohida atomlarning oksidlanish darajalarini aniqlash uchun bir qator qoidalarni qo'llashni so'rashadi (havolaga qarang). Kimyoviy formalizm oksidlanishni oksidlanish darajasining oshishi, qaytarilishini esa oksidlanish darajasining pasayishi sifatida belgilaydi.

Biroq, biologlar odatda bu tarzda redoks reaktsiyalari haqida o'ylamaydilar yoki o'rgatmaydilar. Nega? Biz biologiyada uchraydigan oksidlanish-qaytarilish reaktsiyalarining aksariyati molekulalar o'rtasida elektron (lar)ni o'tkazish natijasida yuzaga keladigan oksidlanish darajasining o'zgarishi bilan bog'liq deb taxmin qilamiz. Shuning uchun biologlar odatda qisqarishni elektronlarning ko'payishi va oksidlanishni elektronlarning yo'qolishi sifatida belgilaydilar. Biz shuni ta'kidlaymizki, oksidlanish-qaytarilish reaktsiyalarining elektron almashinuvining biologik ko'rinishi oksidlanish darajasining o'zgarishi bilan bog'liq bo'lgan umumiy ta'rifga to'liq mos keladi. Elektron almashinish modeli, ba'zan kimyo sinfi kontekstida sodir bo'ladigan elektronlarni uzatishni o'z ichiga olmaydigan redoks reaktsiyalarini tushuntirmaydi. Biologning redoks kimyosiga bo'lgan nuqtai nazari (biologiya kontekstida) aqliy rasmni yaratish nisbatan oson bo'lgan afzalliklarga ega. Mavzuning hech bo'lmaganda asosiy kontseptual rasmini ishlab chiqishda ishtirok etadigan molekulyar tuzilmani ko'p tekshirishni eslash kerak bo'lgan qoidalar ro'yxati yo'q. Biz shunchaki ikki tomon o'rtasidagi almashinuvni tasavvur qilamiz - bir molekula bir yoki bir nechta elektronni ularni qabul qilgan sherikga beradi.

Bu biologiya sinfi uchun biologiya o'qishi bo'lgani uchun biz redoksga "elektronlarni olish/yo'qotish" kontseptsiyasidan yaqinlashamiz. Agar siz allaqachon kimyo darsini olgan bo'lsangiz va bu mavzu sizning biologiya kursingizda biroz boshqacha tarzda taqdim etilgandek tuyulsa, esda tutingki, siz xuddi shu narsani o'rganasiz. Biologlar kimyodan o'rganganlaringizni biologiya kontekstida yanada intuitivroq qilish uchun moslashtirdilar. Agar siz redoks haqida o'rganmagan bo'lsangiz, tashvishlanmang. Agar siz bu erda nima qilmoqchi ekanligimizni tushuna olsangiz, kimyo darsida ushbu tushunchani yoritsangiz, siz bir necha qadam oldinda bo'lasiz. Fikringizni biroz umumlashtirish uchun ishlashingiz kerak bo'ladi.

Keling, ba'zi umumiy reaktsiyalardan boshlaylik

Ikki birikma o'rtasida elektronlarni o'tkazish ushbu birikmalardan biri elektronni yo'qotadi va bitta birikma elektron oladi. Masalan, quyidagi rasmga qarang. Agar biz umumiy reaktsiyani ko'rib chiqish uchun energiya hikoyasi rubrikasidan foydalansak, reaktivlar va mahsulotlarning oldingi va keyingi xususiyatlarini solishtirishimiz mumkin. Reaksiyadan oldin va keyin materiya (narsa) bilan nima sodir bo'ladi? Murakkab A neytral sifatida boshlanadi va musbat zaryadlanadi. B birikmasi neytral sifatida boshlanadi va manfiy zaryadlanadi. Elektronlar manfiy zaryadlanganligi sababli, biz bu reaktsiyani elektronning harakati bilan izohlashimiz mumkin Murakkab A uchun B. Bu mas'uliyatli o'zgarishlarga mos keladi. Murakkab A elektronni yo'qotadi (musbat zaryadlangan bo'ladi) va biz A oksidlangan deb aytamiz. Biologlar uchun ooksidlanishelektron(lar)ni yo'qotish bilan bog'liq. B elektronni oladi (manfiy zaryadlangan bo'ladi) va biz buni aytamiz B qisqargan. Kamaytirishelektronlarning ko'payishi bilan bog'liq. Biz, shuningdek, reaktsiya sodir bo'lganligi sababli (biror narsa sodir bo'ldi), bu jarayonda energiya uzatilgan va/yoki qayta tashkil etilgan bo'lishi kerakligini bilamiz va biz buni tez orada ko'rib chiqamiz.

1-rasm. Yarim reaksiyalar bilan umumiy redoks reaktsiyasi

Muallif: Meri O. Aina

Takrorlash uchun: elektron (lar) yoki molekula yo'qolganda oksidlangan, elektron (lar) keyin boshqa molekulaga o'tishi kerak. Elektron olgan molekula aylanadi, deymiz kamayadi. Birgalikda bu juftlashgan elektron olish-yo'qotish reaktsiyalari deb nomlanadi oksidlanish-qaytarilish reaktsiyasi (qaytarilish-qaytarilish reaksiyasi deb ham ataladi).

Juftlangan yarim reaksiyalar haqidagi bu fikr redoksning biologik kontseptsiyasi uchun juda muhimdir. Elektronlar molekulani kamaytirish uchun "tekin" koinotdan chiqib ketmaydi yoki molekuladan efirga sakrab tushmaydi. Donorlik elektronlar donor molekuladan kelib, boshqa qabul qiluvchi molekulaga o'tkazilishi kerak. Masalan, elektron ustidagi rasmda 2-yarim reaksiyadagi reduktor B molekulasi donordan kelishi kerak - bu hech qanday joydan paydo bo'lmaydi! Xuddi shunday, yuqoridagi 1 yarim reaksiyada A ni tark etgan elektron boshqa molekulaga “qo‘nishi” kerak – u shunchaki koinotdan yo‘qolib qolmaydi.

Shuning uchun, Oksidlanish va qaytarilish reaktsiyalari DOIMA juft bo'lishi kerak. Quyida biz "yarim reaksiyalar" g'oyasini muhokama qilganimizda ushbu fikrni batafsilroq ko'rib chiqamiz.

  • Eslab qolishingizga yordam beradigan maslahat: Mnemonik LEO GER deydi (Lose Eelektronlar = Ooksidlanish va Gain Eelektronlar = Rta'lim) oksidlanish va qaytarilishning biologik ta'riflarini eslab qolishingizga yordam beradi.

2-rasm. “Arslon LEO GER deydi” mnemonikasining figurasi. LEO: Elektronlarni yo'qotish = Oksidlanish. GER: Elektronlarning daromadi = Reduksiya

Muallif: Kamali Sripathi

• Redoks lug'ati chalkash bo'lishi mumkin: Oksidlanish-qaytarilish kimyosini o'rganayotgan talabalar ko'pincha reaksiyalarni tasvirlash uchun ishlatiladigan lug'at bilan chalkashib ketishlari mumkin. Oksidlanish/oksidant va qaytarilish/qaytaruvchi kabi atamalar ko'rinishi va tovushi juda o'xshash, ammo aniq boshqacha narsalarni anglatadi. Elektron donor ba'zan qaytaruvchi deb ham ataladi, chunki u boshqa birikmaning (oksidantning) qisqarishiga (elektronlarning ortishi) sabab bo'lgan birikmadir. Boshqacha qilib aytganda, qaytaruvchi xayriya qilish bu oksidlovchiga elektronlardir qozonish bu elektronlar. Aksincha, elektron qabul qiluvchi oksidlovchi deb ataladi, chunki u boshqa birikmaning oksidlanishiga (elektronlarning yo'qolishiga) sabab bo'ladi. Shunga qaramay, bu shunchaki oksidlovchi ekanligini anglatadi qozonish bo'lgan qaytaruvchidan elektronlar xayriya qilish bu elektronlar. Hali adashyapsizmi?

Ta'riflar haqida o'ylashning yana bir usuli - bu birikmani reduksiya sifatida tasvirlashni yodda tutishdired/ oksidized ni tasvirlab beradi davlat bu birikmaning o'zi ichida, birikmani reduksiya sifatida belgilash bilan birgachumoli/oksidchumoli birikma qanday ta'sir qilishini, kamaytirish yoki oksidlanishni tasvirlaydi boshqa birikma. Esda tutingki, atama qaytaruvchi bilan ham sinonimdir kamaytiruvchi vosita va oksidlovchi bilan ham sinonimdir oksidlovchi vosita. Ushbu lug'atni ishlab chiqqan kimyogarlar ilmiy sudda "o'z-o'zidan yo'g'onlik" ayblovlari bilan tarbiyalanishi kerak va keyin qolganlarga nima uchun ular ataylab bema'ni bo'lishlari kerakligini tushuntirishga majbur bo'lishlari kerak.

Redoksning chalkash tili: tezkor xulosa

1. Murakkabni "qisqartirilgan" deb ta'riflash mumkin - birikmani tasvirlash uchun ishlatiladigan atama davlat

2. Murakkab "qaytaruvchi" bo'lishi mumkin - birikmani tasvirlash uchun ishlatiladigan atama qobiliyat (boshqa narsani kamaytirishi mumkin). Xuddi shu qobiliyatni tavsiflash uchun "kamaytirish agenti" sinonim atamasi ishlatilishi mumkin ("agent" atamasi "biror narsa qila oladigan" narsani anglatadi - bu holda boshqa molekulani kamaytiradi).

3. Murakkab "oksidant" bo'lishi mumkin - birikmani tasvirlash uchun ishlatiladigan atama qobiliyat (u boshqa narsani oksidlashi mumkin). Xuddi shu qobiliyatni tavsiflash uchun "oksidlovchi agent" sinonim atamasi ishlatilishi mumkin ("agent" atamasi "biror narsa qila oladigan" narsani anglatadi - bu holda boshqa molekulani oksidlaydi).

4. Murakkab "qaytarilishi" yoki "oksidlanishi" mumkin - bu atama o'tish yangi holatga

Ushbu atamalarning barchasi biologiyada qo'llanilganligi sababli, "Umumiy biologiya" bo'limida siz ushbu terminologiya bilan tanishishingizni kutamiz. Uni o'rganishga va imkon qadar tezroq foydalanishga harakat qiling - biz atamalarni tez-tez ishlatamiz va har safar atamalarni belgilashga vaqtimiz bo'lmaydi.

Bilimlarni tekshirish testi

Yarim reaksiya

Bu erda biz yarim reaksiya tushunchasini kiritamiz. Biz har bir yarim reaksiyani "to'liq" redoks reaktsiyasida ishtirok etadigan ikkita molekula (ya'ni, donor yoki akseptor) bilan sodir bo'ladigan hodisalarning tavsifi deb o'ylashimiz mumkin. "To'liq" redoks reaktsiyasi ikki yarim reaktsiyani talab qiladi. Quyidagi misolda №1 yarim reaksiya molekulani tasvirlaydi AH ikkita elektron va protonni yo'qotadi va bu jarayonda A+. Bu reaksiya AH ning oksidlanishini tasvirlaydi. Yarim reaksiya №2 molekulani tasvirlaydi B+ bo'lish uchun ikkita elektron va proton olish BH. Bu reaksiya ning qisqarishini tasvirlaydi B+. Ushbu ikki yarim reaktsiyaning har biri kontseptualdir va hech biri o'z-o'zidan sodir bo'lmaydi. Yarim reaksiyada №1 yo'qolgan elektronlar bir joyga borishi KERAK, ular shunchaki yo'qolib keta olmaydi. Xuddi shunday, №2 yarim reaksiyada olingan elektronlar biror narsadan kelib chiqishi kerak. Ular ham yo'q joydan paydo bo'lolmaydi.

Tasavvur qilish mumkinki, №1 yarim reaksiyada yo'qolgan elektronlar uchun potentsial qabul qiluvchilar (elektronlar uchun joy) bo'lib xizmat qiladigan turli xil molekulalar mavjud. Xuddi shunday, №2 yarim reaksiya uchun elektron donorlar (elektronlarning manbai) bo'lib xizmat qiladigan ko'plab potentsial qisqartirilgan molekulalar bo'lishi mumkin. Quyidagi misolda biz molekula bo'lganda nima sodir bo'lishini (reaktsiya) ko'rsatamiz AH molekula uchun elektron donor hisoblanadi B+. Donor va akseptorning yarim reaksiyalarini birlashtirganimizda, biz "to'liq" redoks reaktsiyasini olamiz. Quyidagi rasmda biz bu reaktsiyani "Reaksiya №1" deb ataymiz. Bu sodir bo'lganda, biz ikki yarim reaktsiyalar, deb aytish bog'langan.

3-rasm. Umumiy redoks reaktsiyasi, bunda AH birikmasi B birikmasi bilan oksidlanadi+. Har bir yarim reaksiya elektronlarni yo'qotish yoki olish uchun bitta tur yoki birikmani (yuqoridagi rasmda ko'rsatilganidek, keyingi protonni) ifodalaydi. Yarim reaksiyada №1 AH proton va 2 elektronni yo'qotadi: ikkinchi yarmida B+ 2 ta elektron va bir proton oladi. Bu misolda HA A ga oksidlanadi+ esa B+ BH ga kamayadi.

Ushbu g'oyadan foydalanib, biz har qanday ikki yarim reaktsiyani nazariy jihatdan bog'lashimiz va o'ylashimiz mumkin, bir yarim reaksiya berilgan elektronlarni qabul qiladigan ikkinchi yarmi reaktsiya uchun elektron donor bo'lib xizmat qiladi. Misol uchun, yuqoridagi misoldan foydalanib, biz qisqartirishni birlashtirishni ko'rib chiqishimiz mumkin B+ Bu NADH molekulasining oksidlanishini tavsiflovchi boshqa yarim reaksiya bilan 2-yarm reaksiyada sodir bo'ladi. Bunday holda, NADH elektron donor bo'ladi B+. Xuddi shunday siz 1-yarm reaksiyada sodir boʻladigan AH oksidlanishini Z gipotetik molekulasining qisqarishini tavsiflovchi yarim reaksiya bilan bogʻlashingiz mumkin.+. Yarim reaksiyalarni aralashtirib, bir-biriga moslashtirishingiz mumkin, chunki ularning yarmi birikmaning oksidlanishini (u elektronlar beradi) va boshqa birikmaning qisqarishini (u berilgan elektronlarni qabul qiladi) tavsiflaydi.

  • To'liq reaktsiyalarni yarim reaktsiyalarga qarshi qanday yozishimiz haqida eslatma: Yuqoridagi misolda №1 reaksiyani tenglama sifatida yozganimizda, 2 elektron va H+ asosiy yarim reaktsiyalarda aniq tasvirlangan, to'liq reaktsiya matniga aniq kiritilmagan. Yuqoridagi reaktsiyada siz elektronlar almashinuvi sodir bo'ladi degan xulosaga kelishingiz kerak. Buni har bir reaktiv va uning tegishli mahsuloti o'rtasidagi zaryadlarni muvozanatlashga urinish orqali kuzatish mumkin. Reaktiv AH mahsulotga aylanadi A+. Bunday holda, siz elektronlarning ba'zi harakati sodir bo'lgan degan xulosaga kelishingiz mumkin. Ushbu birikmaning zaryadlarini muvozanatlash uchun (tenglamaning har bir tomonidagi zaryadlar yig'indisini tenglashtiring) tenglamaning o'ng tomoniga 2 ta elektron qo'shishingiz kerak, ulardan biri "+" zaryadini hisobga olish uchun. A+ va H bilan borish uchun bir soniya+ bu ham yo'qolgan. Boshqa reaktiv B+ ga aylantiriladi BH. Shuning uchun zaryadlarni muvozanatlash uchun u 2 ta elektron olishi kerak, biri uchun B+ va qo'shimcha H uchun bir soniya+ bu qo'shildi. Birgalikda bu ma'lumotlar sizni eng ko'p sodir bo'lgan narsa ikki elektron o'rtasida almashinishi degan xulosaga olib keladi. AH va B+.

  • Bu biologiyadagi aksar oksidlanish-qaytarilish reaktsiyalari uchun ham shunday bo'ladi. Yaxshiyamki, aksariyat hollarda reaktsiya konteksti, ko'pincha redoks bilan shug'ullanadigan kimyoviy guruhlarning mavjudligi (masalan, metall ionlari) yoki tez-tez ishlatiladigan elektron tashuvchilarning mavjudligi (masalan, NAD)+/NADH, FAD+/FADH2, ferredoksin va boshqalar) sizni reaksiyaning "redoks" sinfiga tegishli ekanligi haqida ogohlantiradi. Siz ushbu umumiy molekulalarning ba'zilarini tanib olishni o'rganishingiz kutiladi.

Potensialni pasaytirish

An'anaga ko'ra, biz deb nomlangan o'lchov yordamida redoks reaktsiyalarini miqdoriy jihatdan tavsiflaymiz kamaytirish potentsiallari. Qaytarilish potentsiali birikma yoki molekulaning elektron olish yoki yo'qotish "qobiliyatini" miqdoriy jihatdan tavsiflashga harakat qiladi. Kamaytirish potentsialining o'ziga xos qiymati eksperimental tarzda aniqlanadi, ammo ushbu kursning maqsadi uchun biz o'quvchi taqdim etilgan jadvallardagi qiymatlar to'g'ri ekanligini qabul qiladi deb taxmin qilamiz. Biz qisqarish potentsialini antropomorfizatsiya qilishimiz mumkin, bu birikmaning elektronlarni "tortib olishi" yoki "tortib olishi" yoki "ushlashi" mumkin bo'lgan kuch bilan bog'liq. Bu bilan bog'liqligi ajablanarli emas lekin bir xil emas elektromanfiylik.

Elektronlarni jalb qilish uchun bu o'ziga xos xususiyat nima?

Turli birikmalar, ularning tuzilishi va atom tarkibiga ko'ra, elektronlar uchun o'ziga xos va aniq "jozibali" ga ega. Bu sifat har bir molekulaning o'z standartiga ega bo'lishiga olib keladi kamaytirish potentsiali yoki E0. Qisqartirish potentsiali nisbiy miqdordir (ba'zilariga nisbatan "standart"reaktsiya). Agar sinov birikmasi standartga qaraganda elektronlarga nisbatan kuchliroq "tortishuvga" ega bo'lsa (agar ikkalasi raqobatlashsa, sinov birikmasi standart birikmadan elektronlarni "olardi"), biz sinov birikmasi ijobiy qaytarilish potentsialiga ega deb aytamiz. E dagi farqning kattaligi0Har qanday ikkita birikma (shu jumladan standart) o'rtasidagi bog'liqlik birikmalar elektronlarni qanchalik ko'p yoki kamroq "istaganiga" proportsionaldir. Qisqartirish potentsialining nisbiy kuchi o'lchanadi va birliklarda xabar qilinadi Volt (V) (ba'zan elektron volt yoki eV sifatida yoziladi) yoki milliVolts (mV). Aksariyat redoks minoralarida mos yozuvlar birikmasi H2.


Mumkin NB muhokamasi Nuqta

O'zingiz uchun takrorlang: Elektromanfiylik tushunchasi va qizil / ho'kiz potentsiali o'rtasidagi farqni qanday tasvirlaysiz yoki o'ylaysiz?


Redoks talabalarining noto'g'ri tushunchasi haqida ogohlantirish: Murakkabning standart oksidlanish-qaytarilish potentsiali moddaning vodorodga nisbatan elektronni qanchalik kuchli ushlab turishini bildiradi. Oksidlanish-qaytarilish potentsiali ham, elektromanfiylik ham biror narsaning elektronni qanchalik "xohlashini" o'lchash sifatida muhokama qilinganligi sababli, ular ba'zan bir-biri bilan aralashib ketadi yoki chalkashib ketadi. Biroq, ular bir xil emas. Molekuladagi atomlarning elektron manfiyligi uning oksidlanish-qaytarilish potentsialiga ta'sir qilishi mumkin bo'lsa-da, bu yagona omil emas. Bu qanday ishlashi haqida tashvishlanishingizga hojat yo'q. Hozircha ularni turli va o'ziga xos g'oyalar sifatida ongingizda saqlashga harakat qiling. Ushbu ikki tushuncha o'rtasidagi jismoniy munosabatlar ushbu umumiy biologiya sinfining doirasidan tashqarida.

Redoks minorasi

Oksidlanish-qaytarilish reaksiyalarida barcha turdagi birikmalar qatnashishi mumkin. Olimlar oksidlanish-qaytarilish-qaytarilish minorasi grafik vositasini ishlab chiqdilar, u E.0' qiymatlar. Ushbu vosita potentsial elektron donorlari va qabul qiluvchilar o'rtasidagi elektron oqimining yo'nalishini va ma'lum bir reaktsiyada qancha erkin energiya o'zgarishini kutish mumkinligini taxmin qilishga yordam beradi. An'anaga ko'ra, jadvaldagi barcha yarim reaktsiyalar ro'yxatga olingan har bir birikma uchun pasayish yo'nalishi bo'yicha yoziladi.

Biologiya kontekstida elektron minora odatda turli xil umumiy birikmalarni (ularning yarim reaktsiyalarini) eng salbiy E dan ajratib turadi.0' (elektronlardan osongina xalos bo'ladigan birikmalar), eng ijobiy E0' (elektronlarni qabul qilish ehtimoli yuqori bo'lgan birikmalar). Quyidagi minorada har bir reaksiyada uzatiladigan elektronlar soni ko'rsatilgan. Masalan, NADning kamayishi+ NADH ga ikkita elektron kiradi, ular jadvalda 2e sifatida yozilgan-.

oksidlangan shakl

qisqartirilgan shakl

n (elektronlar)

Eo' (volt)

PS1* (ho'kiz)

PS1* (qizil)

-

-1.20

Asetat + CO2

piruvat

2

-0.7

ferredoksin (ho'kiz) versiya 1

ferredoksin (qizil) versiya 1

1

-0.7

suksinat + CO2 + 2H+

a-ketoglutarat + H2O

2

-0.67

PSII* (ho'kiz)

PSII* (qizil)

-

-0.67

P840* (ho'kiz)

PS840* (qizil)

-

-0.67

asetat

asetaldegid

2

-0.6

glitserat-3-P

glitseraldegid-3-P + H2O

2

-0.55

O2

O2-

1

-0.45

ferredoksin (ho'kiz) versiya 2

ferredoksin (qizil) versiya 2

1

-0.43

CO2

glyukoza

24

-0.43

CO2

formatlash

2

-0.42

2H+

H2

2

-0,42 (da [H+] = 10-7; pH=7)

Eslatma: [H+] = 1; pH=0 vodorod uchun Eo' nolga teng. Buni kimyo darsida ko'rasiz.

a-ketoglutarat + CO2 + 2H+

izotsitrat

2

-0.38

asetoatsetat

b-gidroksibutirat

2

-0.35

Sistin

sistein

2

-0.34

Piruvat + CO2

malat

2

-0.33

NAD+ + 2H+

NADH + H+

2

-0.32

NADP+ + 2H+

NADPH + H+

2

-0.32

Kompleks I FMN (ferment bilan bog'langan)

FMNH2

2

-0.3

Lipoik kislota (ho'kiz)

Lipoik kislota (qizil)

2

-0.29

1,3 bifosfogliserat + 2H+

glitseraldegid-3-P + Pi

2

-0.29

Glutation, (ho'kiz)

Glutation, (qizil)

2

-0.23

FAD+ (bepul) + 2H+

FADH2

2

-0.22

Asetaldegid + 2H+

etanol

2

-0.2

Piruvat + 2H+

laktat

2

-0.19

Oksalatsetat + 2H+

malat

2

-0.17

a-ketoglutarat + NH4+

glutamat

2

-0.14

FAD+ + 2H+ (bog'langan)

FADH2 (bog'langan)

2

0.003-0.09

Metilen ko'k, (ho'kiz)

Metilen ko'k, (qizil)

2

0.01

Fumarat + 2H+

suksinatsiya qilish

2

0.03

CoQ (Ubiquinone - UQ + H+)

UQH.

1

0.031

UQ + 2H+

UQH2

2

0.06

Dehidroaskorbin kislotasi

askorbin kislotasi

2

0.06

plastokinon; (ho'kiz)

plastokinon; (qizil)

-

0.08

Ubiquinone; (ho'kiz)

Ubiquinone; (qizil)

2

0.1

Kompleks III Sitokrom b2; Fe3+

Sitokrom b2; Fe2+

1

0.12

Fe3+ (pH = 7)

Fe2+ (pH = 7)

1

0.20

Kompleks III Sitokrom c1; Fe3+

Sitokrom c1; Fe2+

1

0.22

sitoxrom c; Fe3+

sitoxrom c; Fe2+

1

0.25

IV majmua sitoxrom a; Fe3+

sitoxrom a; Fe2+

1

0.29

1/2 O2 + H2O

H2O2

2

0.3

P840GS (ho'kiz)

PS840GS (qizil)

-

0.33

IV majmua Sitokrom a3; Fe3+

Sitokrom a3; Fe2+

1

0.35

Ferrisiyanid

ferrosiyanid

2

0.36

sitoxrom f; Fe3+

sitoxrom f; Fe2+

1

0.37

PSIGS (ho'kiz)

PSIGS (qizil)

.

0.37

Nitrat

nitrit

1

0.42

Fe3+ (pH = 2)

Fe2+ (pH = 2)

1

0.77

1/2 O2 + 2H+

H2O

2

0.816

PSIIGS (ho'kiz)

PSIIGS (qizil)

-

1.10

* Yorug'lik fotonni yutgandan keyin hayajonlangan holat

GS asosiy holati, yorug'lik fotonni yutishdan oldingi holat

PS1: kislorodli fototizim I

P840: Bakterioxlorofilni o'z ichiga olgan bakterial reaktsiya markazi (anoksigen)

PSII: kislorodli fototizim II

1-jadval. Bis2A da ishlatiladigan umumiy redoks minorasi. An'anaga ko'ra, minora yarim reaktsiyalari birikmaning oksidlangan shakli chap tomonda va qaytarilgan shakli o'ngda yoziladi. Yaxshi elektron donorlarni hosil qiluvchi birikmalar juda salbiy qaytarilish potentsialiga ega. Glyukoza va vodorod gazi kabi birikmalar mukammal elektron donorlardir. Aksincha, kislorod va nitrit kabi mukammal elektron qabul qiluvchilarni hosil qiluvchi birikmalar mukammal elektron qabul qiluvchilardir.

Elektron minora haqida video

Oksidlanish-qaytarilish muammolarida elektron minoradan qanday foydalanish haqida qisqacha videoni olish uchun bu yerga yoki pastga bosing. Bu video doktor Easlon tomonidan Bis2A talabalari uchun tayyorlangan. (Bu juda ma'lumotli.)

O'rtasidagi munosabatlar qanday DE0' va DG?

Har qanday redoks reaktsiyasi (ikki yarim reaksiyaning o'ziga xos kombinatsiyasi) energetik ravishda o'z-o'zidan yoki yo'qligini (ekzergonik yoki endergonik) qanday bilamiz? Bundan tashqari, ma'lum bir oksidlanish-qaytarilish reaktsiyasi uchun erkin energiyaning miqdoriy o'zgarishi qanday ekanligini qanday aniqlash mumkin? Javob ikki birikmaning qisqarish potentsialidagi farqda yotadi. Reaksiyaning qaytarilish potentsialidagi farq (E0'), E o'rtasidagi farqni hisobga olgan holda hisoblanishi mumkin0' uchun oksidlovchi (birikma elektronlarni oladi va boshqa birikmaning oksidlanishiga sabab bo'ladi) va qaytaruvchi (elektronlarni yo'qotadigan birikma). Quyidagi umumiy misolimizda AH qaytaruvchi va B+ oksidlovchi hisoblanadi. Elektronlar AH dan B ga o'tadi+. E dan foydalanish0' Qaytaruvchi uchun -0,32 va oksidlovchi uchun +0,82 E ning umumiy o'zgarishi0' yoki E0' 1,14 eV ni tashkil qiladi.

4-rasm. Qaytarilish potentsiali bilan yozilgan yarim reaktsiyalar bilan umumiy qizil / ho'kiz reaktsiyasi (E0') ko'rsatilgan ikki yarim reaksiyadan.

∆E0Oksidlovchi va qaytaruvchi o'rtasidagi taklif elektron uzatishning o'z-o'zidan paydo bo'lishi haqida bizga xabar berishi mumkin. Intuitiv ravishda, agar elektronlar elektronlarni "xohlagan" birikmadan ko'chirish taklif qilinsa Kamroq elektronlarni "xohlovchi" birikmaga Ko'proq (ya'ni harakat dan pastroq bo'lgan birikma E0'uchun yuqori bo'lgan birikma E0', reaktsiya energetik ravishda o'z-o'zidan bo'ladi). Agar elektronlar elektronni ko'proq "xohlaydigan" birikmadan kamroq elektronni "xohlaydigan" birikmaga o'tish taklif qilinsa (ya'ni harakat dan yuqori bo'lgan birikma E0'uchun pastroq bo'lgan birikma E0', reaktsiya energetik ravishda o'z-o'zidan bo'lmagan bo'ladi). Biologik/biokimyoviy redoks jadvallari buyurtma qilinganligi sababli (kichik E0' tepada va kattaroq E0' pastki qismida) elektronlarning stol ustidagi donorlardan pastroqdagi qabul qiluvchilarga o'tishi o'z-o'zidan bo'ladi.

Bundan tashqari, ma'lum bir oksidlanish-qaytarilish reaktsiyasi bilan bog'liq bo'lgan erkin energiya o'zgarishi miqdorini aniqlash mumkin. Bu munosabat Nernst tenglamasi bilan berilgan:

5-rasm. Nernst tenglamasi oksidlanish-qaytarilish reaktsiyasining erkin energiyasini reaksiyaning qaytarilgan mahsulotlari va oksidlangan reaktiv o'rtasidagi qaytarilish potentsialidagi farq bilan bog'laydi.
Muallif: Mark T. Facciotti

Qayerda:

  • n - uzatilgan elektronlarning mol soni
  • F - Faraday doimiysi 96,485 kJ/V. Ba'zan u 23,062 kkal/V bo'lgan kkal/V birliklarida beriladi, ya'ni bir mol elektron 1 voltlik potentsial pasayishdan o'tganda ajralib chiqadigan energiya miqdori (kJ yoki kkal).

E'tibor bering, ∆E va ∆G belgilari bir-biriga qarama-qarshidir. ∆E musbat bo'lsa, ∆G manfiy bo'ladi. ∆E manfiy bo'lsa, ∆G musbat bo'ladi.


Sitokrom C

Barcha hujayralar omon qolish uchun muhim metabolik jarayonlarni boshqarish uchun ATP, adenozin trifosfat shaklida energiya talab qiladi. Aerob organizm ovqatni hazm qilganda glyukoza (C6H12O6) glikoliz jarayonida piruvatning ikkita molekulasiga parchalanadi. Qisqartirilgan elektron tashuvchilar, NADH va FADH2 Ushbu reaksiyaning qo'shimcha mahsuloti sifatida ishlab chiqariladi.

NAD + ikkita elektron (2e - ) va vodorod ionini (H + ) oladi va NADH hosil qiladi. Xuddi shunday, FAD FADH hosil qilish uchun ikkita vodorod ionini (2H + ) va ikkita elektronni (2e - ) qabul qiladi.2. Bu elektronlar NADH va FADH dan2 keyin Elektron tashish zanjirining komplekslariga kiring. Elektron tashish zanjiri (ETC) mitoxondriyaning ichki membranasida joylashgan elektron transport oqsillari seriyasidir - hujayraning quvvat manbai (1-rasm). Mitoxondriyal membranada bir qator redoks-faol oqsillar joylashgan bo'lib, ular elektronlarni ETC orqali o'tkazish orqali sim kabi ishlaydi. Bir qator oksidlanish-qaytarilish reaktsiyalari orqali bu oqsillar protonlarni (H +) mitoxondriyal matritsadan membranalararo bo'shliqqa pompalaydi. Membranlararo bo'shliqda protonlarning to'planishi ATP sintaza fermenti tomonidan ATP sintezini ta'minlaydigan elektrokimyoviy gradient hosil qiladi. Elektron tashish zanjiri jami 34 ta ATP molekulasini ishlab chiqaradi, bu hujayradan omon qolish uchun metabolik jarayonlarni amalga oshirish uchun foydalanishi mumkin. 1

1-rasm. Elektron tashish zanjiri

Bu elektron transport zanjiri (ETC) haqida umumiy ma'lumot. ETC to'rtta protein kompleksidan iborat: NADH dehidrogenaza, suksinat dehidrogenaza, sitoxrom bc.1, va sitoxrom c oksidaz, mitoxondriyaning ichki membranasiga o'rnatilgan. Ushbu oqsil komplekslari orqali elektronlar uzatilganda, mitoxondriyaning membranalararo bo'shlig'ida proton (H +) gradienti to'planadi. ATP Synthase ETC tomonidan o'rnatilgan ushbu proton gradientidan ATP shaklida energiya sintez qilish uchun foydalanadi.

2-rasm. Sitokrom C ning to'liq uzunlikdagi lenta tuzilishi (PDB 3cyt). 3 Bu bitta sitoxrom c monomerining biologik birikmasidir. Markaziy gem ichida to'q sariq rangda ko'rsatilgan temir ioni mavjud. Gem sitoxromlarda topilgan takrorlanuvchi Cys-X-Y-Cys-His motivi tufayli mumkin bo'lgan disulfid aloqalari orqali oqsil bilan kovalent bog'lanadi.

Sitokrom c ATP sintezi uchun elektron transport zanjirining muhim tarkibiy qismidir (2-rasm). Sitokrom c suvda eriydigan elektron transport oqsili bo'lib, mitoxondriyal ichki membrana bilan erkin bog'langan. Elektron tashish zanjirida sitoxrom c elektron tashish zanjirining uchinchi kompleksi sitoxrom bc dan gem guruhi orqali bir vaqtning o'zida bitta elektronni uzatadi.1, elektron tashish zanjirining to'rtinchi kompleksiga, sitoxrom c oksidaza. 2

Sitokrom c uning funktsiyasi uchun zarur bo'lgan gem temir metall markazini o'z ichiga oladi. Elektronlarni tashish jarayonida bu gem temir Fe 3+ va Fe 2+ oksidlanish darajalari o'rtasida o'zgaradi, bu elektronlarni qabul qilish va berish imkonini beradi. 4 Sitokrom c oksidlangan shaklda bo'lganda, elektron sitoxrom bc dan o'tadi.1 Gema Fe 3+ ga murakkab, uni Fe 2+ ga kamaytiradi. Nihoyat, sitoxrom c elektronni ETC ning oxirgi elektron tashuvchisi, sitoxrom c oksidazaga chiqaradi. Bu vaqtda temir markazi Fe 3+ oksidlanish holatiga qaytadi.

C sitoxromining temir metall markazi markaziy temir ioni atrofida olti ligandning koordinatsiyasi tufayli oktaedral geometriyani ifodalaydi (3-rasm). Oktaedral geometriya sitoxrom c uchun afzaldir, chunki 6 ta elektronga boy ligandlarning har biri musbat zaryadlangan metall temir ionini barqarorlashtirishga hissa qo'shadi. To'q sariq rangda ko'rsatilgan gem temiri qattiq kvadrat tekis porfirin halqasining to'rtta azot atomi va ikkita eksenel ligandlar tomonidan muvofiqlashtiriladi: metionin qoldig'ining oltingugurt atomi va histidin imidazol halqasining azot atomi. Tsitoxrom c ning porfirin halqasi tetradentat xelatlovchi ligand hisoblanadi, chunki porfirin halqasining to'rtta azot atomi markaziy temir bilan bog'lanib, barqaror organometall kompleks hosil qiladi. Xelat ta'siriga asoslanib, bu tetradentat ligandni bog'lash joyi bir xil metall ioniga monodentat ligandning yaqinligi bilan solishtirganda entropik jihatdan qulayroqdir. 5

Sitokrom c ning ligandlari qattiq yumshoq kislota asoslari nazariyasiga asoslanadi. (HSAB). HSAB kislota va asoslarni qattiq, yumshoq yoki chegaradosh deb tasniflaydi. Yumshoq kislotalar va asoslar kattaroq va oson qutblanadigan, qattiq kislotalar va asoslar esa kichikroq va kamroq qutblanuvchan. Qattiq va yumshoq o'rtasida joylashgan turlar chegara hisoblanadi. 6 HSABga asoslanib, chegaradagi temir gistidin imidazol halqasining azoti (chegara chizig'i asosi), porfirin halqasi tomonidan ta'minlangan azot atomlari (chegara asoslari) va metionin oltingugurti (yumshoq asos) bilan muvofiqlashishi mantiqan to'g'ri. ).

3-rasm. Sitokrom C 3 ning temir metall markazi

3A-rasmda sitoxrom c ning butun tuzilishi ko'rsatilgan, 3B-rasmda esa sitoxrom c ning elektron tashish funksiyasi uchun zarur bo'lgan gem-temir metall markazining kattalashtirilgan qismi ko'rsatilgan. To'q sariq rangda ko'rsatilgan gem temir qattiq kvadrat tekis porfirin halqasining to'rtta azot atomi (ko'k) va ikkita eksenel ligandlar tomonidan muvofiqlashtiriladi: metionin qoldig'ining oltingugurt atomi (sariq) va histidin imidazol halqasining azot atomi (ko'k). ).

C sitoxromining temir metall markazi markaziy temir ioni atrofida olti ligandning koordinatsiyasi tufayli oktaedral geometriyani ifodalaydi (3-rasm). Oktaedral geometriya sitoxrom c uchun afzaldir, chunki 6 ta elektronga boy ligandlarning har biri musbat zaryadlangan metall temir ionini barqarorlashtirishga hissa qo'shadi. To'q sariq rangda ko'rsatilgan gem temiri qattiq kvadrat tekis porfirin halqasining to'rtta azot atomi va ikkita eksenel ligandlar tomonidan muvofiqlashtiriladi: metionin qoldig'ining oltingugurt atomi va histidin imidazol halqasining azot atomi. Tsitoxrom c ning porfirin halqasi tetradentat xelatlovchi ligand hisoblanadi, chunki porfirin halqasining to'rtta azot atomi markaziy temir bilan bog'lanib, barqaror organometall kompleks hosil qiladi. Xelat ta'siriga asoslanib, bu tetradentat ligandni bog'lash joyi bir xil metall ioniga monodentat ligandning yaqinligi bilan solishtirganda entropik jihatdan qulayroqdir. 5

Sitokrom c ning ligandlari qattiq yumshoq kislota asoslari nazariyasiga asoslanadi. (HSAB). HSAB kislota va asoslarni qattiq, yumshoq yoki chegaradosh deb tasniflaydi. Yumshoq kislotalar va asoslar kattaroq va oson qutblanadigan, qattiq kislotalar va asoslar esa kichikroq va kamroq qutblanuvchan. Qattiq va yumshoq o'rtasida joylashgan turlar chegara hisoblanadi. 6 HSABga asoslanib, chegaradagi temir gistidin imidazol halqasining azoti (chegara chizig'i asosi), porfirin halqasi tomonidan ta'minlangan azot atomlari (chegara asoslari) va metionin oltingugurti (yumshoq asos) bilan muvofiqlashishi mantiqan to'g'ri. ).

Elektronlarni tashish jarayonida gem temir metall markazi oksidlanish darajasini o'zgartirsa ham, sitoxrom c temirdagi oksidlanish darajasidan qat'i nazar, har doim oktaedral, past spinli geometriyani qabul qiladi. 7 Ushbu geometriya Ligand Field Stabilization Energy (LFSE) asosida tanlanadi. LFSE - nazariy barisentrga nisbatan metall kompleksining d-elektronlarining umumiy energiyasi. LFSE ni aniqlash formulasi quyidagi 1- tenglamada ko'rsatilgan, bu erda x= kam energiya t dagi d-elektronlarning soni2g orbitallar va y= yuqori energiyadagi d-elektronlar soni eg orbitallar.

4-rasm. Past Spin Fe 3+ va Fe 2+ ning LFSE bo'linish diagrammasi

Elektron bo'linish diagrammalari va kam spinli Fe 3+ va Fe 2+ uchun hisoblar mos ravishda A va B rasmlarida ko'rsatilgan. Past spinli temir uchun yuqori spinli temir bilan solishtirganda ko'proq salbiy LFSE qiymatlari bu past aylanish konformatsiyasi energiya jihatidan qulayroq ekanligini va shuning uchun kompleks qabul qiladigan konfiguratsiya ekanligini ko'rsatadi.

5-rasm. Yuqori spinli Fe 3+ va Fe 2+ ning LFSE bo'linish diagrammalari

Yuqori spinli Fe 3+ va Fe 2+ uchun nazariy elektron boʻlinish diagrammalari va hisoblar mos ravishda A va B rasmlarda koʻrsatilgan. Biroq, LFSE qiymatlari oksidlanish darajasidan qat'i nazar, past spinli temir uchun yuqori spinli temirga qaraganda salbiyroqdir. Shuning uchun, sitoxrom c ning gem temir metall markazi temirdagi oksidlanish darajasidan qat'i nazar, har doim past spinli oktaedral geometriyani qabul qiladi.

Past spin holatida d-elektronlar kam energiyali t da juftlashadi2g yuqori energiyani egallashdan oldin orbitallar eg orbitallar, bu barqarorlikni oshiradi. Yuqori spin holatida d-elektronlar ikkala t ni ham birma-bir egallaydi2g va eg orbitallarning energiyasini hisobga olmagan holda, keyin esa juftlashadi. LFSE qanchalik salbiy bo'lsa, kompleks shunchalik barqaror. Past spinli temir uchun LFSE qiymatlari temirda mavjud bo'lgan oksidlanish holatidan qat'i nazar, yuqori spinli temir uchun LFSE qiymatlariga qaraganda salbiyroqdir. Shunday qilib, sitoxrom c ning temir metall markazi har doim energiya jihatidan qulayroq past aylanish konformatsiyasini qabul qiladi.

Elektronlarni tashish jarayonida sitoxrom c ning gem temiri +2 va +3 oksidlanish darajalari orasida aylanadi. Sitokrom c elektron tashish zanjirining uchinchi kompleksidan elektronni qabul qilganligi sababli, sitoxrom bc.1, Fe 3+ temir metall markazi Fe 2+ ga kamayadi. Sitokrom c bu elektronni elektron tashish zanjirining oxirgi kompleksi - sitoxrom c oksidazaga chiqarganda, Fe 3+ oksidlanish holati tiklanadi. Biroq, temirning oksidlanish holatidagi bu o'zgarishga qaramasdan, gem muvofiqlashtirish temir ionini o'zgartirmaydi &ldquolocked &rdquo va minimal qayta tashkil etishdan o'tadi.

Reduksiya potentsiali ETCda sitoxrom c ning elektron tashish funktsiyasini ham osonlashtiradi. Qaytarilish potentsiali (E o &rsquo) kimyoviy turning elektron olish va shuning uchun kamayishi tendentsiyasidir. Qaytarilish potentsiali qanchalik ijobiy bo'lsa, o'sha kimyoviy turning elektronni qabul qilish va qisqarish tendentsiyasi shunchalik yuqori bo'ladi. Sitokrom BC uchun pasayish potentsiali1 (ETK ning III kompleksi) 0,194 V. Sitokrom miloddan avvalgi1 sitoxrom c ning oksidlangan shakliga (Fe 3+) bitta elektron beradi, sitoxrom c temirini bir oksidlanish darajasiga kamaytirib, Fe 2+ ga aylanadi. C sitoxromining qisqarish potentsiali 0,254 V ni tashkil qiladi. Sitokrom c oksidazasining (ETK ning IV kompleksi) reduksiya potentsiali 0,562 V ni tashkil qiladi. 8 Sitokrom C oksidaza sitoxrom c ni o'z holatiga qaytaradigan sitoxrom c (Fe 2+) dan elektronni qabul qiladi. oksidlangan shakl (Fe 3+). Elektron tashish zanjirining komplekslari oksidlanish-qaytarilish potentsialini oshirish tartibida joylashtirilgan (har bir kompleks oldingisiga qaraganda elektronlarga nisbatan yuqoriroq yaqinlikka ega), bu elektronlar oqimini Elektron tashish zanjirining yakuniy kompleksi - sitoxrom C oksidaza tomon harakatga keltiradi.

E o &rsquodonor < E o &rsquo elektron uzatish oqsili/markazi < E o &rsquoakseptor: Reaktsiya o'z-o'zidan bo'lishi uchun haqiqat bo'lishi kerak!

Xulosa qilib aytadigan bo'lsak, sitoxrom c muhim elektron uzatish oqsili bo'lib, elektronlarni ETC ning III va IV komplekslari o'rtasida o'tkazadi. Gem temir metall markazi Fe 3+ va Fe 2+ o'rtasida osongina o'zaro aylanadi, bu elektronlarni qabul qilish va berish imkonini beradi. Agar bu elektron uzatish sodir bo'lmasa, mushaklar harakati, DNK sintezi va faol transport kabi ko'plab metabolik jarayonlarni ta'minlash uchun zarur bo'lgan ATP ishlab chiqarilmaydi. Shu sababli, sitoxrom c bu ATP ishlab chiqarishni sitokrom C oksidazaga elektron o'tkazish orqali osonlashtiradigan muhim komponent bo'lib, hujayralarga tirik qolish uchun zarur bo'lgan ushbu hayotiy jarayonlarni amalga oshirish uchun zarur bo'lgan energiyani ta'minlaydi. 9


Mitoxondriyaning oksidlovchi fosforillanishi (diagramma bilan)

Fosforlanishning oksidlanish metabolizmi bilan aloqasi birinchi marta 1930-yillarda taklif qilingan.

Birinchi dalil TCA siklining oraliq moddalari hujayralar tomonidan metabolize qilinganda fosfatning muhitdan chiqarilishi kuzatildi.

Keyinchalik, noorganik fosfatning yo'qolishi glyukoza-6-fosfat va fruktoza-6-fosfat kabi organik fosfatlarning to'planishi bilan birga bo'lganligi ko'rsatildi.

Ko'p o'tmay, ATP oksidlovchi fosforlanishning asosiy mahsuloti sifatida tan olindi. 1948 yilda Kennedi va Leninger bu oksidlanish va fosforlanish faqat mitoxondriyalarda sodir bo'lishini aniqladilar. 1951 yilga kelib, Leninger NADH ning organellalarga kirishiga imkon berish uchun ishlov berilgan mitoxondriyalarga NADH va H + qo'shish orqali Krebs sikli reaktsiyalarini butunlay chetlab o'tish mumkinligini ko'rsatdi. Har bir qo'shilgan NADH va H + uchun uchta fosfat va bitta kislorod iste'mol qilindi va shuning uchun elektron tashish zanjiri ATP sintezi uchun muhim degan xulosaga keldi.

The potential differences of the reactions of elec­tron transfer beginning with NAD + -dehydrogenases and ending with cytochrome oxidase provide the en­ergy to drive the endergonic oxidative phosphoryl­ation. The exergonic reactions can be summarized as

Which has a ∆G 0 ‘ of -220.5 kJ/mole (-52.7 kcal/ mole). The endergonic reactions summarized as

are associated with a standard free energy of at least 91.6 kJ (i.e., ∆G 0 ‘= 30.5 kJ/mole or 7.3 kcal/mole). The efficiency of the coupling of the two systems is at least 42% (i.e., 91.6/220.5). The stages at which coupling occurs are known. Figure 16-25 shows the major energy changes along the electron transfer chain. The step from NADH to Q represents the reactions of the dehydrogenases that link NAD + and FP to Q.

This reaction sequence (Site I) provides enough energy (51.0 kJ/mole or 12.2 kcal/ mole) for the formation of the first of three ATPs ob­tained by NADH oxidation. The step from Q to cyto­chrome b does not provide enough energy for the second phosphorylation, but the following step (from cytochrome b to cytochrome c) does yield sufficient energy (Site II).

The step from cytochrome c to cyto­chrome a is only moderately exergonic, but the final step from cytochrome a to oxygen is highly exergonic (Site III). Thus, a pair of electrons transferred from one carrier to the next by these oxidation-reduction reactions at three places in the chain generates the energy for the formation of ATP.

However, not all elec­trons from oxidized substrates enter the electron transport chain at the initial NAD + position. Some electrons, like those from succinate, pass from the co­enzyme of succinate dehydrogenase (i.e., FAD) di­rectly to Q. When this happens, only two ATPs are formed per pair of electrons transferred.

Molecular Events in Oxidative Phosphorylation:

The mechanism by which energy from the electron transport system is used for oxidative phosphoryl­ation is far from clear. It would appear that there are yet to be discovered coupling factors and enzymes in­volved in the process.

Among the more significant ob­servations that have been made are the identification of:

(1) Mechanisms for controlling the rate of electron transport and oxidative phosphorylation,

(2) Inhibi­tors that can prevent ATP formation or uncouple elec­tron transport from oxidative phosphorylation,

(3) Partial oxidative phosphorylation reactions, and

Maximal electron transport in mito­chondria can occur only if there is ample ADP and P available to act as an acceptor of inorganic phosphate.

When ADP is lacking or when ATP is plentiful, the rate of respiration is low and is called state 4 respira­tion (Fig. 16-26). When ADP is added, the rate of oxygen consumption rises as the ADP is phosphoryla- ted. This elevated level of respiration is called state 3 respiration. Once the ADP is consumed, state 4 respi­ration is reestablished.

The influence of ADP in respi­ratory rate is called acceptor or respiratory control, the “acceptor” being ADP. Interestingly, the configu­ration of mitochondria changes between state 4 and state 3 respiration. During state 4 respiration, the mitochondrion assumes the orthodox conformation but changes to the condensed conforma­tion when added ADP induces state 3.

A number of chemical agents uncouple oxidative phosphorylation from the electron transport system (e.g., 2, 4-dinitrophenol, dicumarol, and the salicyl- anilides). The addition of these compounds has two in­teresting effects. First, they speed up electron trans­port and oxygen consumption even in the absence of ADP, but there is no synthesis of ATP. In other words, phosphorylation is uncoupled and so is energy trans­fer. Second, in the presence of the uncoupling agent, the hydrolysis of ATP may occur—the opposite of the normal goals of mitochondrial activity.

Oligomycin is an inhibitor of oxidative phosphoryl­ation and coupled oxygen consumption but it does not prevent electron transfer in uncoupled systems. A group of agents called ionophores also prevent oxida­tive phosphorylation by dissipating the energy needed for phosphorylation. Ionophores are only effective in the presence of certain monovalent cations such as K + and Na + .

Some of the reactions of oxidative phosphorylation are known. An ATPase is present in the inner mem­brane and is stimulated by 2, 4-dinitrophenol but inhib­ited by oligomycin. Another reaction is the exchange of inorganic phosphate with the terminal phosphate of ATP, a reaction called phosphate-ATP exchange. This reaction is inhibited by both 2, 4-dinitrophenol and oli­gomycin.

An exchange of atoms also occurs between the oxygen’s of water and those of inorganic phos­phate, called phosphate-water exchange. The terminal phosphate can also be exchanged between ATP and ADP, a process inhibited by 2, 4-dinitrophenol and oli­gomycin and called the ADP-ATP exchange reaction. Some interesting studies that relate structure and function in mitochondria have been carried out using inverted submit ochondrial vesicles formed from frag­ments of the inner membrane. In these studies, the in­ner membranes of mitochondria isolated from cells are subjected to sonification or detergent action.

The resulting fragments of the cristael membranes then round up to form vesicles with the inner membrane spheres on the outside surface (Fig. 16-27). If closed vesicles are formed, they exhibit functioning electron transport system and oxidative phosphorylation reac­tions. There is no ATP formation with open vesicles or non-vesicular fragments, but electron transport still occurs.

If the submitochondrial vesicles are treated with urea or trypsin, the inner membrane spheres are re­moved and can be separated from the vesicles, which lose their capacity to carry out oxidative phosphoryl­ation. However, if the spheres are added back to the vesicles, the capacity to perform oxidative phospho­rylation is regained. The spheres contain ATPase/ synthetase, which is called coupling factor one (F,). This enzyme has been purified and found to have a molecular weight of about 360,000, a diameter of 9 nm, and a requirement for Mg 2 .

In intact mitochon­dria the enzyme is bound to the membrane and also catalyzes the synthesis of ATP and ADP and inor­ganic phosphate, rather than the reverse, and as such could be termed ATP-synthetase. The isolated en­zyme’s function, however, is not inhibited by oligomy­cin. Another factor has been isolated that when present with isolated F1 renders the ATPase sensitive to oligomycin.

This latter factor is called F0 or oligomycin-sensitivity-conferring protein (OSCP). F0 is also a large protein it is speculated that F0 could constitute at least part of the stalk that attaches the sphere to the inner membrane.


How do you know a redox reaction has taken place?

In most of chemistry, we know a reaction has taken place if a bond is made or broken. Lekin ichida electrochemistry, a redox reaction has taken place if an electron has been transferred from one atom to another. This process powers everything from batteries to electroplating and can power energy-intensive processes.

Most of the time, electrons are gained and lost by metals, because those are the easiest to oxidize and reduce. So if you see a compound with a metal in solution, check its oxidation potentials and compare it to the other reactant. Does one need more electrons? Does one have electrons that are easily given up? If both are true, you might be looking at a redox reaction.

If all the atoms have enough electrons (or none to give up), then a redox reaction will not take place.

Once all electrons have been transferred, you can figure out what will happen with the rest of the reactants in the solution and balance the equation. Sometimes, the counter ions will switch from one place to another to balance the charge, producing different amounts of product. You’ll need some stoichiometry to figure out exactly how much. It’s also important to know the rules for assigning oxidation states in order to make sure you’ve identified the correct potential (removing one electron from sodium is much easier than removing two!).

But once you know how to figure out whether an electron is ready for a big night out with its atomic friends or if it would rather stay in, you’ll be well on your way to some fascinating electrochemistry.

[box type=”success” align=”” width=””]For more information check out the Oksidlanish-qaytarilish (qaytarilish-qaytarilish) reaksiyalari lesson in our AP Chemistry course or Elektrokimyo lesson in our General Chemistry course.[/box]


Mechanism of the reduction and oxidation reaction of cytochrome c at a modified gold electrode

Maqola koʻrishlar soni 2008-yil noyabr oyidan buyon barcha muassasalar va shaxslar boʻyicha toʻliq matnli maqola yuklab olishlarining COUNTER-mos keluvchi yigʻindisidir (PDF va HTML). Ushbu ko'rsatkichlar so'nggi bir necha kungacha bo'lgan foydalanishni aks ettirish uchun muntazam ravishda yangilanadi.

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Eslatma: Annotatsiya o'rniga bu maqolaning birinchi sahifasi.


The course provides an opportunity for an in-depth study of a topic of current interest selected annually. Discussion and research of the literature is encouraged as a means of examining both scientific aspects of the topic and the relationship of science to societal, legislative, and economic issues. Prerequisite: senior status or permission of instructor. Liberal Arts Core/University Requirements Designation: DSINQ. (2)

A continuation of the study that began in BIO 441 that further examines nucleic acid function, including topics such as nucleotide biosynthesis, gene expression and regulation, DNA replication and repair, and RNA transcription and processing. In addition, an in-depth study of the regulation and integration of metabolic pathways will be emphasized. Prerequisite: BIO 441. (3)


Oxidation-reduction reactions between cobalt(II) and -(III) chelate and iron(III) and -(II) cyanide complexes. Outer- vs. inner-sphere mechanisms

Maqola koʻrishlar soni 2008-yil noyabr oyidan buyon barcha muassasalar va shaxslar boʻyicha toʻliq matnli maqola yuklab olishlarining COUNTER-mos keluvchi yigʻindisidir (PDF va HTML). Ushbu ko'rsatkichlar so'nggi bir necha kungacha bo'lgan foydalanishni aks ettirish uchun muntazam ravishda yangilanadi.

Iqtiboslar - bu Crossref tomonidan hisoblangan va har kuni yangilanadigan ushbu maqolaga havola qilingan boshqa maqolalar soni. Crossref iqtiboslar soni haqida ko'proq ma'lumot oling.

Altmetrik e'tibor reytingi tadqiqot maqolasi onlaynda olingan e'tiborning miqdoriy o'lchovidir. Donut belgisini bosish altmetric.com saytida ushbu maqola uchun ball va ijtimoiy media mavjudligi haqida qo'shimcha ma'lumotlar bilan sahifani yuklaydi. Altmetrik e'tibor balli va ball qanday hisoblanishi haqida ko'proq ma'lumot oling.

Eslatma: Annotatsiya o'rniga bu maqolaning birinchi sahifasi.


The Oxygen-Evolving Center (OEC) of Photosystem II

Photosynthesis is the process by which plants make energy from the use of chlorophyll and light. It is the process that oxidizes (removes electrons from) water to produce dioxygen and sustains all life on earth. 1 It sustains all life through the food chain. Light from the sun initiates photosynthesis in plants, which is turned into energy. Animals eat plants in order to receive energy. Humans can eat those animals or vegetarians can eat the plants and the energy gets transferred again. Prokaryotic cells have an organelle, called a chloroplast, that harvests sunlight and produces energy in the form of ATP. Inside the chloroplast there are stacks called grana and cytoplasm called stroma. Inside the grana (also known as thylakoids) are Photosystem I and II. 2 The process through which sunlight gets transferred to Photosystem II is depicted in Figure 1 below. Photosystem II (PSII) is the first major complex in the photosynthetic electron transport chain. It is the only molecule in photosynthesis that can produce dioxygen from water and light.

Figure 1. This image depicts the sun producing light energy, which is then absorbed by the plant in its chloroplast. Inside the chloroplast there are stroma, thylakoid, and granum. The stroma is the aqueous fluid that holds the different parts together. The thylakoid contains Photosystem I and II, which are key molecules to the function of the photosynthetic electron transport chain. The granum is stacks of thylakoids. Photosystem II is the main focus here. It is embedded in the membrane of the thylakoid. The top part of PSII is exposed to the stroma, and the bottom part is in the lumen. The lumen represents the area inside the thylakoid membrane. This image was created using Notability.

Studying Photosystem II is of particular interest right now for engineers developing photovoltaic solar panels to harvest light energy and use it as a renewable resource. Photosystem II has the most efficient light transformative capability on earth. If engineers and scientists could break down water splitting in the molecule and apply it to cell potential of photovoltaic cells then solar panels could have the possibility of reaching nearer to 100% efficiency.

The sunlight energy obtained by Photosystem II is used to extract electrons from water molecules through certain proteins and enzymes. Two water molecules break into oxygen gas and hydrogen ions, and the freed oxygen gas is the source of oxygen available for us to breath. 3

This can be displayed in the chemical Equation 1:

1) 2H2O &rarr O2 + 4e - + 4H + Reduction Potential=0.815V

The hydrogen ions produced in this reaction are later used to power up ATP synthesis. The four electrons are transferred in the process are passed down a chain of electron-carrying proteins. These electrons are used to pump the hydrogen ions across the membrane, which give even more power to ATP synthesis. Photosystem I helps the electrons along the way to the final destination of photosynthesis. The electrons are finally delivered to enzymes that produce sugar from water and carbon dioxide (also known as the Calvin cycle). 1 The photosynthesis chain can be depicted in Figure 2 below.

Figure 2. Present here is the photosynthetic electron transport chain. The first step takes place in Photosystem II. The photons from light are captured through antennas and electrons are then extracted from water molecules. The water molecule is broken into oxygen gas and hydrogen ions through the oxygen evolving center (OEC), which will be further discussed in the paper. The electrons are used to pump the hydrogen ions across the membrane, and are transferred through the Electron Transport Chain to Photosystem I. 1 The final fate of the hydrogen ions is to power up ATP synthesis, and the final fate of the electrons is to be placed on a carrier molecule NADPH. 2 ATP synthesis drives the production of ATP. This ATP is then used to construct organic molecules from carbon dioxide and water. NADPH is used to help turn carbon dioxide into glucose. This image was created using ChemDraw and Notability.

At the reaction center of PSII is the oxygen evolving center (OEC). It is proposed that the metal-oxygen cluster is a cubane shape with the formula Mn3CaO4. 4 There are two OECs present in each functional unit of Photosystem II, as shown below in Figure 3. The OEC is responsible for oxidizing 2 H2O to O2 (Equation 1 above). 5

Figure 3. The beige complex shows the full structure of the molecule, Photosystem II. It is partially embedded in the thylakoid membrane. The part of PSII that resides in the stroma is where light is absorbed. Arrows point to the di-oxygen evolving centers (OECs) present in Photosystem II. The OECs reside in the lumen. The purple portion of the OEC depicts the manganese and the red portion depicts the oxygen. The one green corner in the cube is the Ca 2+ . Image was created in Powerpoint using PDB code 1s5l and USCF Chimera.

The OEC is held in the protein by histidine, aspartate, glutamate, and alanine side chains. 1 In this way, the protein is acting like a multi dentate chealtor. The chelate effect occurs when a ligand has the ability to bind to a metal ion through multiple donor atoms. When the ligand binds through more than one atom it is termed a chelating ligand (or chelator), and a ligand that binds through more than one donor atom it is termed a polydentate system. Chelating ligands typically have lone pairs that can bind to metal ions on two or more of its atoms. There is an energy benefit due to entropy in the chelate effect called the entropic benefit. This comes into play in the OEC and increases the stability of the complex resulting in a greater entropic advantage. The OEC in Photosystem II is a cubane cluster of multiple ions, including manganese and calcium ions, that are bridged through oxygen ions. 4 The structure of the OEC is depicted in Figure 4 below. The OEC is bound to the protein through amino acid side chains, all which bind to the OEC directly through the manganese and oxygen ions. Although this is not a simple case of one metal ion being chelated through multiple donor groups, if the OEC is treated as one unit, then the protein can be considered a polydentate system.

Figure 4. The image above depicts the catalytic center where the oxidation of water takes place. Here you can see that the Mn3CaO4 cluster is held in place by histidine, aspartate, glutamate, and alanine side chains. The structure is still a bit ambiguous because X-ray analysis has shown to distort the protein when analyzed. The EXFAS (extended x-ray absorption fine structure) reveals the structure shown above containing the Mn-Mn and the Mn-ligand interactions. 3 The final structure deduced is the Mn1--3 present in the cube with Ca, and Mn4 hanging off of the cube. Image was created using ChemDraw.

Each manganese in the cubane cluster of the OEC has different ligands. The geometry around each individual metal center is octahedral, meaning they are each coordinated by six ligands. Mn1 has an Asp, three oxygen that are part of the cube, and two possible water molecules as its ligands. Mn2 has Glu, His, three oxygens that are part of the cube, and a possible water molecule as its ligands. Mn3 has Glu as a ligand, which could be one or two coordinated, and three oxygens that are part of the cube as its other ligands. Mn4 has Glu, Asp, a bicarbonate acting as a tridentate bridge with Ca +2 , and two water molecules as its ligands. The calcium has the bicarbonate tridentate as a ligand and a carbonyl of an Ala as another ligand. The other ligands of calcium are water or hydroxide ions. 6

As stated previously, the metal centers in Photosystem II are manganese and calcium. 6 Ca is only found as Ca 2+ and its d-electron count is 0. Mn is found in the metal oxidation states of Mn 2+ , Mn 3+ , Mn 4+ , Mn 5+ . 7 Mn 2+ has a d electron count of 5, Mn 3+ has a d-electron count of 4, Mn 4+ has a d electron count of 3, and Mn 5+ has a d electron count of 2. All first row transition metals (Mn included) are high spin. High spin correlates to a small delta and contributes to a weak field. Only d 4 -d 7 transition metals can contribute to a high or low spin. Mn 4+ and Mn 5+ are d 3 and d 2 metals respectively so they do not have high or low spin states for octahedral geometry. The oxygens in place help stabilize these highly positive Mn ions. Mn 2+ and Mn 3+ both contribute to a high spin. In an experiment, all Mns were reduced to Mn 2+ . The Mn 2+ came out of the complex because it was labile and had 0 ligand field stabilization energy (LFSE). 6

The LFSE splitting diagrams for the five metals in the OEC and the calculations for LFSE can be seen in Figure 5 below. The more negative the value for LFSE the more stable it is. Therefore, Mn 4+ is the most stable because it has a LFSE value of -1.2. Mn 2+ and Ca 2+ both have a LFSE value of 0 so they are the least stable. However, they are the most labile meaning they are very fast to react. Overall, if there are more electrons in the antibonding eg orbitals (seen in Figure 5 below) then the metal is more labile. Mn 3+ has a LFSE value of -0.6 and Mn 5+ has an LFSE value of -0.8. These two oxidation states are relatively stable and not very labile.

Figure 5. Ligand Field Stabilization Energy (LFSE) calculations can be seen here along with the octahedral orbital filling diagrams. The key here is if there are more electrons in the antibonding eg orbitals then the metal is more labile, which means it is able to react very fastly. Mn 2+ va Ca 2+ are the most labile, but the least stable because of their LFSE values of 0. Mn 4+ is the least labile and the most stable with a LFSE value of -1.2. These calculations were drawn out with Notability.

The wide range of oxidation states of Mn is an advantage for its role in water oxidation of PSII. How this exactly happens is through the photocatalytic process. The OEC is oxidized in a series of oxidation steps losing one electron at a time at each step. There are five states that have been observed spectroscopically and they are S0, S1, S2, S3, S4. 3 The full cycle can be seen in Figure 6 below. UV-visible spectroscopy have showed changes in oxidation state of Mn 2+ to Mn 3+ and Mn 3+ to Mn 4+ throughout the cycle.

The photocatalytic process (water splitting) will be described in simplistic terms. The OEC is oxidized in a series of oxidation steps, and this happens at the same time the chlorophyll complex (P680) gets excited from light. Four photons must be absorbed in order to excite the P680. The Mn IV 2Ox group is unaltered throughout the cycle so it not shown besides in the S0 state. From the S0 state to the S1 state there is a redox reaction taking place, and Mn 2+ is oxidized to Mn 3+ . The electron goes to P680. From the S1 state to the S2 state there is another redox reaction taking place. Mn 3+ is oxidized to Mn 4+ , and the electron lost also goes to P680. From the S2 state to the S3 state there is another redox reaction taking place, but the electron is transferred through a tyrosine radical. The tyrosine is present to help transfer the electrons from the OEC to P680. It acts almost as a bridge making the two dependent on each other. From the S3 state to the S4 state there is a ligand dissociation, with an unknown base. Finally from the S4 state to the S0 state there is a ligand exchange present where the O2 is released. This whole process is happens at light speed. The final result is that it produces a dioxygen and a hydrogen ion. The roles of Ca 2+ are uncertain in the OEC cycle. It is important to note that the OEC acts a redox catalyst throughout the cycle, and also as an electron transport center when the electrons from the OEC get passed to P680.

Figure 6. The photocatalytic cycle relates photon absorption, manganese oxidation, and water oxidation. The catalytic cycle is rather complex and not fully understood. However, it is known that four photons must be absorbed in order to generate the cycle. The (Mn IV 2Ox) group is unaltered throughout the cycle so it not shown besides in the S0davlat. The tyr represents a tyrosine residue, and the B represents an unknown Lewis base. From the S0state to the S1 state there is a redox reaction taking place. From the S1 state to the S2 state and from the S2 state to the S3state there is also redox reactions taking place. From the S3 state to the S4state there is a ligand dissociation. Finally from the S4 state to the S0state there is a ligand exchange present where the O2ozod qilinadi. Created with Notability. dan moslashtirilgan Metals and Life textbook. 3

As mentioned, there lies a special pair of chlorophyll molecules (P680) at the center of PSII along with the OEC. The special pair of chlorophyll molecules are Chlorophyll A and B, and they make up the P680 complex. They are special because they act as excitonic dimer, meaning they behave in function as a single entity. 8 The 680 refers to the complex&rsquos absorption maximum in the visible light spectrum (680 nm= red absorption). It reflects green light around 500 nm, which is why we see plants as green.The reduction potential of P680 is very high (around 1.2 to 1.4 V). This is required of the water splitting reaction (S-cycle) in the OEC for oxidizing water into O2 and H + . 9 The reduction potential of the dioxygen is 0.815 V (see Equation 1 above). Since this reduction potential is less than the reduction potential of P680, the four electrons are from the OEC are easily transferred to the P680. Figure 7 below gives the reduction potentials of relevant parts of PSII and the reduction potential of Photosystem I. 3 The arrows show which way the electrons flow. When they point down the flow is spontaneous and when they point up the flow is non-spontaneous.

Figure 7. This graph shows a simplified version of the reactions involved in photosynthesis. Z represents the OEC with a tyrosine residue. You can see that the reduction potential of Z is less than that of P680 so the electrons spontaneously flow to P680. The four electrons in the P680 get excited from a photon of light and are promoted to a higher energy level. The electrons then flow through QA, PQ, and C which are all part of the Electron Transport Chain. Finally the electrons go to Photosystem I, and the process of photosynthesis continues. Created with Notability. dan moslashtirilgan Metals and Life textbook. 3

The Z represents the OEC along with the neighboring tyrosine residue. As the OEC enters into the photocatalytic process it passes its electrons freely to P680. As the photon of light is absorbed by P680 it gets excited and non-spontaneously transfers the four electrons to Quinone A (QA). QA is bound to plastoquinone (PQ). QA, PQ, and C are all contribute to the electron transport chain that pass the electrons onto Photosystem I. 3 This all happens at speed of light, and explains why photosynthesis can sustain life on earth. It all starts with the complex molecule of Photosystem II, which scientists and engineers are racing to synthetically mimic in order to solve the energy crisis.

(1) Goodsell, D. S. Photosystem II. RCSB Protein Data Bank 2004.

(2) Mason, K. A. Losos, J. B. Singer, S. R. Raven, P. H. Biologiya, Eleventh edition. McGraw-Hill Education: New York, NY, 2017.

(3) Metals and Life Crabb, E., Moore, E., Open University, Eds. RSC Pub: Cambridge, U.K, 2010.

(4) Photosystem II. Vikipediya 2017.

(5) Biological inorganic chemistry structure and reactivity University Science Books: Sausalito, California, 2007.

(6) Atkins, P. W. Shriver & Atkins&rsquo Inorganic Chemistry V.H. Freeman and Co.: New York, 2010.

(7) VCAC: Cellular Processes: Photosystem II: First Look http://vcell.ndsu.edu/animations/photosystemII/first.htm (accessed Apr 4, 2018).

(8) Raszewski, G. Diner, B. A. Schlodder, E. Renger, T. Spectroscopic Properties of Reaction Center Pigments in Photosystem II Core Complexes: Revision of the Multimer Model. Biofizika jurnali 2008, 95 (1), 105&ndash119.

(9) Ferreira, K. N. Iverson, T. M. Maghlaoui, K. Barber, J. Iwata, S. Architecture of the


Redox regulation of the G1 to S phase transition in the mouse embryo fibroblast cell cycle

The hypothesis that intracellular oxidation/reduction (redox) reactions regulate the G(0)-G(1) to S-phase transition in the mouse embryonic fibroblast cell cycle was investigated. Intracellular redox state was modulated with a thiol-antioxidant, N-acetyl-L-cysteine (NAC), and cell cycle progression was measured using BrdUrd pulse-chase and flow cytometric analysis. Treatment with NAC for 12 h resulted in an approximately 6-fold increase in intracellular low-molecular-weight thiols and a decrease in the MFI of an oxidation-sensitive probe, dihydrofluorescein diacetate, indicating a shift in the intracellular redox state toward a more reducing environment. NAC-induced alterations in redox state caused selective delays in progression from G(0)-G(1) to S phase in serum-starved cells that were serum stimulated to reenter the cell cycle as well as to inhibit progression from G(1) to S phase in asynchronous cultures with no significant alterations in S phase, and G(2)+M transits. NAC treatment also showed a 70% decrease in cyclin D1 protein levels and a 3-4-fold increase in p27 protein levels, which correlated with decreased retinoblastoma protein phosphorylation. Cells released from the NAC treatment showed a transient increase in dihydrofluorescein fluorescence and oxidized glutathione content between 0 and 8 h after release, indicating a shift in intracellular redox state to a more oxidizing environment. These changes in redox state were followed by an increase in cyclin D1, a decrease in p27, retinoblastoma protein hyperphosphorylation and subsequent entry into S phase by 8-12 h after the removal of NAC. These results support the hypothesis that a redox cycle within the mammalian cell cycle might provide a mechanistic link between the metabolic processes early in G(1) and the activation of G(1)-regulatory proteins in preparation for the entry of cells into S phase.


Yordamchi ma'lumotlar

Variation of the oxygen chemical potential, ΔμO(T,p), as a function of the temperature (T) and pressure (p), side and top view of the and of the SCV (001) magnetite surfaces, variation of the Bader charge of the Fe atoms following the creation of an oxygen vacancy, top view of the (2 × 2) unit cell of A′ surface, side view of half of the slabs of A, B, B′, and surface with an added oxygen atom, apdos of the Fe atoms of bulk, A surface, B, and B′ surface, total dos of bulk, A surface, B, and B′ surface, and band structure of bulk, A surface, B, and B′ surface (PDF)


Videoni tomosha qiling: KAĞITTAN YAY VE OK YAPIMI - Çok Kolay (Avgust 2022).