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Nima uchun aminokislotalar kislotali va asosiy aminokislotalarning funktsional guruhlarida bog'lanmaydi?

Nima uchun aminokislotalar kislotali va asosiy aminokislotalarning funktsional guruhlarida bog'lanmaydi?



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Aspartat va histidin kabi "kislotali" va "asosiy" aminokislotalar mavjud.

Ushbu aminokislotalar bilan oqsil sintez qilinganda, yig'iladigan aminokislotalar polipeptiddagi aminokislotalarning funktsional guruhlaridagi amin guruhlari yoki kislotali guruhlar bilan bog'lanmasligini nima ta'minlaydi?


Aminokislota ribosomaga kelganda, u aminokislotalarning karboksil guruhi tRNKning 3' uchida joylashgan riboza qismining 3' OH guruhi bilan esterifikatsiyalangan aminoatsil tRNK shaklida bo'ladi.

Ribosomaning P joyida -NH bilan reaksiyaga kirishadigan erkin -COOH guruhi bilan bog'langan o'sib borayotgan peptid allaqachon mavjud.2 Keyingi peptid bog'lanishni hosil qilish uchun A joyiga kiruvchi aminokislotalar guruhi. Bu reaksiya asosan ferment faol sayt bo'lgan kontekstda sodir bo'ladi. Reaktivlar kataliz sodir bo'lishi uchun to'g'ri holatda bo'ladi (bu holda kataliz kichik ribosoma RNKning ribozim faolligi bilan amalga oshiriladi).

Demak, javob shuki, bu reaksiyaning selektivligi fermentlarning yuqori o'ziga xos reaksiyalarni amalga oshirishga qodir bo'lgan yo'llarining yana bir misolidir. Masalan, 6-o'rinda glyukozani fosforillaydigan geksokinaza fermenti, kimyoviy jihatdan fosforlangan bo'lishi mumkin bo'lgan to'rtta boshqa -OH guruhiga ega.


Menimcha, peptid aloqalari yon zanjirlarda sodir bo'lishi mumkin. @AlanBoyd ta'kidlagan sabablarga ko'ra, bu an'anaviy peptid sintezida sodir bo'lmaydi va printsipial jihatdan bu erda savolga javobdir.

Eslatma qo'shish uchun:

Ribosomal bo'lmagan peptid sintazalari ko'plab keyingi noodatiy modifikatsiyalar bilan peptidlarni ishlab chiqarishi mumkin. Agar siz bakitratsinning tuzilishiga nazar tashlasangiz, men ishonamanki, katta halqa halqaning boshqa uchida lizin amin va aminokislota karboksilati orasidagi kondensatsiya natijasida yopiladi. Boshqa ko'plab misollar bo'lishi kerak.

Ikkilamchi metabolizm deb ataladigan yo'llar juda ko'p turli xil birikmalarni hosil qiladi - deyarli hamma narsa mumkin ko'rinadi.


Nima uchun aminokislotalar kislotali va asosiy aminokislotalarning funktsional guruhlarida bog'lanmaydi? - Biologiya

Prolin alifatik guruh bilan ko'p xususiyatlarni baham ko'radi.

Prolin rasmiy ravishda aminokislota EMAS, balki an imino kislotasi. Shunga qaramay, u aminokislota deb ataladi. Glutamat yarimaldegidning &alfa uglerodidagi birlamchi amin aldegid bilan Shiff asosini hosil qiladi, keyinchalik u kamayadi va prolin hosil qiladi.

Prolin peptid bog'ida bo'lsa, u &alfa amino guruhida vodorodga ega emas, shuning uchun u &alfa spiral yoki &beta varaqni barqarorlashtirish uchun vodorod bog'ini bera olmaydi. Ko'pincha prolin &alfa spiralida bo'lolmaydi, deb noto'g'ri aytiladi. &alfa spiralida prolin topilsa, vodorod bog'i yo'qligi sababli spiral biroz egilib qoladi.

Prolin ko'pincha &alfa spiralning oxirida yoki burilish yoki halqalarda joylashgan. Deyarli faqat tarkibida mavjud bo'lgan boshqa aminokislotalardan farqli o'laroq trans- polipeptidlarda hosil bo'ladi, prolin tarkibida bo'lishi mumkin cis-peptidlardagi konfiguratsiya. The cis va trans shakllari deyarli izoenergetikdir. The cis/trans izomerizatsiya oqsillarni katlamada muhim rol o'ynashi mumkin va bu kontekstda ko'proq muhokama qilinadi.


Sisteinning oksidlanishi

Sisteinning tiol (oltingugurt o'z ichiga olgan) guruhi yuqori reaktivdir. Bu guruhning eng keng tarqalgan reaksiyasi disulfid hosil qiluvchi qaytar oksidlanishdir. Ikki molekula sisteinning oksidlanishi sistinni hosil qiladi, molekula tarkibida disulfid bog'i mavjud. Proteindagi ikkita sistein qoldig'i bunday bog'lanishni hosil qilganda, u disulfid ko'prigi deb ataladi. Disulfid ko'prigi tabiatda ko'plab oqsillarni barqarorlashtirish uchun ishlatiladigan keng tarqalgan mexanizmdir. Bunday disulfid ko'priklar ko'pincha hujayralardan ajralib chiqadigan hujayradan tashqari oqsillar orasida uchraydi. Eukaryotik organizmlarda disulfid ko'priklarining shakllanishi endoplazmatik retikulum deb ataladigan organella ichida sodir bo'ladi.

Hujayradan tashqari suyuqliklarda (masalan, qon) sisteinning sulfgidril guruhlari tez oksidlanib, sistin hosil qiladi. Tsistinuriya deb ataladigan genetik kasallikda sistinning siydik bilan ko'p miqdorda chiqarilishiga olib keladigan nuqson mavjud. Sistin aminokislotalarning eng kam eriydigani bo'lganligi sababli, chiqarilgan sistinning kristallanishi buyraklar, siydik yo'llari yoki siydik pufagida toshlar, odatda "toshlar" deb ataladigan toshlar paydo bo'lishiga olib keladi. Toshlar kuchli og'riq, infektsiya va siydikda qonga olib kelishi mumkin. Tibbiy aralashuv ko'pincha d -penitsilaminni kiritishni o'z ichiga oladi. Penitsilamin sistin bilan kompleks hosil qilish orqali ishlaydi, bu kompleks faqat sistindan 50 baravar ko'proq suvda eriydi.

Xulosa qilib aytganda, oqsilning shakli va biologik funktsiyasini, shuningdek, uning fizik va kimyoviy xossalarini aniqlaydigan aminokislotalarning ketma-ketligi. Shunday qilib, oqsillarning funktsional xilma-xilligi oqsillar 20 xil turdagi aminokislotalarning polimerlari bo'lganligi sababli yuzaga keladi. Masalan, "oddiy" protein - bu 51 ta aminokislotadan iborat bo'lgan insulin gormoni. Ushbu 51 pozitsiyaning har birida jami 20 51 yoki taxminan 10 66 dan tanlab olish uchun 20 xil aminokislotalar bilan nazariy jihatdan turli xil oqsillarni hosil qilish mumkin edi.


Tsvitterion shaklidagi aminokislota

Karboksil guruhi kislotali va aminokislota guruhi asosli bo'lganligi sababli, ikkalasi fiziologik pHda konjugatsiyalangan zaryadlangan shakllarda zvitterion sifatida mavjud bo'ladi. Keyingi maqolamda zvitterion va aminokislota zaryadlari haqida batafsil ma'lumot (keyingi havola).

Alohida aminokislotalarni parchalashdan oldin bitta yakuniy tushuncha - bu 3 o'lchovli oqsil tuzilishi. Biologik tizimda tuzilishi funksiyani belgilaydi, shuning uchun aminokislotalarning xususiyatlarini tushunish strukturani va oxir-oqibat oqsil funktsiyasini tushunish uchun kalit hisoblanadi.

3-D oqsilning asosiy tuzilishi
Protein tuzilishini aniqlashning birinchi va muhim omili aminokislotalarning ketma-ketligidir. Agar polipeptid zanjiri boshqa tartibda biriktirilsa, siz juda boshqacha umumiy tuzilishga ega bo'lasiz.

3 o'lchamli oqsilning ikkilamchi tuzilishi
Ikkilamchi struktura magistral vodorod bog'lanish o'zaro ta'siridan kelib chiqadi. Peptid aloqasi har bir oldingi karboksil va aminokislotalarni amid funktsional guruhiga aylantiradi. Alfa spiral va beta qatlamli qatlamlarning ikkilamchi tuzilishi karbonildagi qisman manfiy kislorod va azotdagi qisman musbat vodorod o'rtasidagi vodorod bog'lanishidan kelib chiqadi.

3 o'lchamli oqsilning uchinchi darajali tuzilishi
Uchinchi darajali struktura - bu haqiqiy 3 o'lchovli katlama joriy qilingan joy va bu birinchi marta yon zanjirning o'zaro ta'sirini sezasiz. BU erda aminokislotalar yon zanjirlarini bilish va tushunish juda muhimdir.

O'zimni takrorlayman, uchinchi darajali tuzilish polipeptid zanjirida o'zgaruvchan R-guruh yon zanjiri o'zaro ta'sirini birinchi marta ko'rasiz. Ko'pgina talabalar buni ikkilamchi tuzilma bilan chalkashtirib yuborishadi, bu faqat orqa miya o'zaro ta'siri.

3 o'lchamli ko'p polipeptidli oqsilning to'rtlamchi tuzilishi
To'rtlamchi tuzilish deganda bitta kattaroq oqsil hosil qilish uchun turli polipeptidlar orasidagi o'zgaruvchan guruh o'zaro ta'siri tushuniladi.

To'rtlamchi tuzilmalar har bir oqsilda uchramaydi. Agar oqsilda faqat bitta aminokislota zanjiri bo'lsa, unda eng yuqori qatlamlanish darajasi uning uchinchi darajali tuzilishidir. Ammo, agar oqsil bir nechta polipeptid bo'linmalaridan iborat bo'lsa, unda to'rtlamchi tuzilish turli polipeptidlarni bir-biriga bog'lab turadi.

Endi yon zanjir xususiyatlarining ahamiyatini tushunganingizdan so'ng, keling, aminokislotalar bilan tanishaylik. Yodda tutingki, asosiy aminokislotalar va karboksil guruhlari birlamchi/ikkilamchi tuzilish bilan band bo'lganligi sababli, yon zanjirning xususiyatlari va xususiyatlarini o'rganishda ular tahlil qilinmaydi.
Bu siz karboksil va aminokislotalarning har qanday potentsial polaritesini e'tiborsiz qoldirishingizni va FAQAT yon zanjirlarga qarashingizni anglatadi.


Kislota va asos: kislotalar haqida asoslar

Kimyoda biz molekulalar (o'zlari atomlardan tashkil topgan) haqida gapiramiz. Asosiy molekula yoki birikma kislotaga qarama-qarshidir. Kislotalar vodorod ionini (H+) asosga beradigan birikmalardir, asosli birikma esa protonni (H+ - proton) kislotadan ajrata oladigan birikmalardir. Kuchli asos molekulasi suv kabi kuchsizroq kislotani deprotonatsiya qilishi yoki protonini olishi mumkin.

Suv, kislotalar va ishqorlar

Vodorod molekulalari nima uchun asoslar va kislotalar ko'pincha pH darajasida o'lchanadi (pH "vodorod potentsiali" degan ma'noni anglatadi) toza suv bilan bog'liq. pH shkalasi 0 dan 14 gacha. Toza suvning pH darajasi 7, aniq o'rtada.

Kislota suvda eritilsa, u suvga qaraganda yuqori vodorod ionlari faolligiga ega bo'lgan eritmaga aylanadi, bu esa uni kislotaliroq qiladi, pH qiymatiga ega. Kamroq 7. Asos suvda eriganda, u suvga qaraganda vodorod faolligi past bo'lgan eritma hosil qiladi va pH qiymatini beradi. kattaroq dan 7. Suvda eriydigan asoslar ishqorlar deyiladi. Xulosa qilish uchun:

  • Toza suv
    • pH darajasi: 7
    • Toza suv odamlar tomonidan yutib yuborilishi mumkin, na korroziy, na gidroksidi va inson terisini kuydirmaydi.
    • pH darajasi: 7 dan kam (<7)
    • Lotin tilidan olingan kislotasi yoki acer, nordon degan ma'noni anglatadi.
    • Kislotalar korroziydir.
    • Kislotalar ishqorlar bilan birlashganda kislotaliligini yo'qotadi.
    • Misollar: limon kislotasi (limon sharbati), sirka kislotasi (sirka), oshqozon kislotasi va akkumulyator kislotasi.
    • pH darajasi: (>7) dan yuqori
    • Suvda eriydigan asoslar ishqorlar yoki ishqoriy moddalar deb ham ataladi.
    • Ishqorlar kaustikdir.
    • Yuqori konsentratsiyada korroziv modda kimyoviy kuyishga olib keladi.
    • Misollar: dengiz suvi, soda, ammiak, bog 'ohak va kuchli lye.

    Xulosa qilish uchun: pH shkalasi bo'yicha toza suvdan qanchalik uzoqlashsangiz, modda shunchalik korroziv yoki kaustik bo'ladi va shuning uchun inson terisi uchun zararli (masalan,). Kislotalarning past qismida siz apelsin sharbatini ichishingiz mumkin, pastki qismida esa dengiz suvida suzishingiz mumkin. Kislotalarning yuqori qismida sizda akkumulyator kislotasi, asoslarning yuqori qismida esa 1999 yildagi filmdan eslab qolishingiz mumkin bo'lgan oqartiruvchi, drenaj tozalagich va lye mavjud. Jang klubi. Bu Bred Pitt qahramoni Edvard Nortonning terisiga inson tupurigini lyo bilan aralashtirib, "Bu kimyoviy kuyish. <. > Siz suvdan foydalanishingiz va uni yomonlashtirishingiz yoki kuyishni zararsizlantirish uchun sirka ishlatishingiz mumkin" deganida sodir bo'ldi. Sirka pH shkalasi bo'yicha 2 ball bo'lib, lie kabi kuchli asosni zararsizlantirishi mumkin bo'lgan kislotadir (pH shkalasida 13).


    3.2.1. Proteinlar genlar tomonidan aniqlangan noyob aminokislotalar ketma-ketligiga ega

    1953 yilda Frederik Sanger protein gormoni bo'lgan insulinning aminokislotalar ketma-ketligini aniqladi (3.22-rasm). Bu ish biokimyoda muhim ahamiyatga ega, chunki u birinchi marta oqsilning aniq belgilangan aminokislotalar ketma-ketligiga ega ekanligini ko'rsatdi.. Bundan tashqari, insulin faqat α-aminokislotalar va α-amino va α-karboksil guruhlari orasidagi peptid aloqalari bilan bog'langan l-aminokislotalardan iborat ekanligini ko'rsatdi. Bu yutuq boshqa olimlarni turli xil oqsillarning ketma-ketligini o'rganishga undadi. Haqiqatan ham, 100 000 dan ortiq oqsillarning to'liq aminokislotalar ketma-ketligi hozir ma'lum. Ajablanarlisi shundaki, har bir oqsil o'ziga xos, aniq belgilangan aminokislotalar ketma-ketligiga ega. Proteinning aminokislotalar ketma-ketligi ko'pincha uning deb ataladi asosiy tuzilish.

    3.22-rasm

    Sigir insulinining aminokislotalar ketma-ketligi.

    1950-yillarning oxiri va 1960-yillarning boshlarida oʻtkazilgan bir qator chuqur tadqiqotlar oqsillarning aminokislotalar ketma-ketligi genetik jihatdan aniqlanganligini koʻrsatdi. DNKdagi nukleotidlar ketma-ketligi, irsiyat molekulasi, RNKdagi nukleotidlarning to'ldiruvchi ketma-ketligini, o'z navbatida, oqsilning aminokislotalar ketma-ketligini belgilaydi. Xususan, repertuarning 20 ta aminokislotalarining har biri uchta nukleotidning bir yoki bir nechta o'ziga xos ketma-ketligi bilan kodlangan (5.5-bo'lim).

    Aminokislotalar ketma-ketligini bilish bir necha sabablarga ko'ra muhimdir. Birinchidan, oqsilning ketma-ketligini bilish, odatda, uning ta'sir qilish mexanizmini (masalan, fermentning katalitik mexanizmi) tushuntirish uchun juda muhimdir. Bundan tashqari, yangi xususiyatlarga ega bo'lgan oqsillarni ma'lum oqsillar ketma-ketligini o'zgartirish orqali hosil qilish mumkin. Ikkinchidan, aminokislotalar ketma-ketligi oqsillarning uch o'lchovli tuzilmalarini aniqlaydi. Aminokislotalar ketma-ketligi DNKdagi genetik xabar va oqsilning biologik funktsiyasini bajaradigan uch o'lchovli struktura o'rtasidagi bog'liqlikdir. Aminokislotalar ketma-ketligi va oqsillarning uch o'lchovli tuzilmalari o'rtasidagi munosabatlarni tahlil qilish polipeptid zanjirlarining katlanishini tartibga soluvchi qoidalarni ochib beradi. Uchinchidan, ketma-ketlikni aniqlash molekulyar patologiyaning tarkibiy qismi, tez o'sib borayotgan tibbiyot sohasi. Aminokislotalar ketma-ketligidagi o'zgarishlar anormal funktsiya va kasalliklarga olib kelishi mumkin. O'roqsimon hujayrali anemiya va kist fibrozi kabi og'ir va ba'zan o'limga olib keladigan kasalliklar oqsil tarkibidagi bitta aminokislota o'zgarishi natijasida yuzaga kelishi mumkin. To'rtinchidan, oqsilning ketma-ketligi uning evolyutsiya tarixi haqida ko'p narsalarni ochib beradi (7-bobga qarang). Proteinlar aminokislotalar ketma-ketligi bo'yicha bir-biriga o'xshaydi, agar ularning umumiy ajdodi bo'lsa. Binobarin, evolyutsiyadagi molekulyar hodisalarni aminokislotalar ketma-ketligidan kuzatish mumkin molekulyar paleontologiya tadqiqotning gullab-yashnagan sohasi hisoblanadi.


    Yigirmata umumiy aminokislotalarga qisqacha qo'llanma

    Kattalashtirish uchun bosing

    Tirik organizmlarni tashkil etuvchi oqsillar ulkan molekulalardir, lekin ular aminokislotalar deb nomlanuvchi kichikroq qurilish bloklaridan iborat. Tabiatda 500 dan ortiq aminokislotalar mavjud, ammo ulardan inson genetik kodi faqat 20 tasini to'g'ridan-to'g'ri kodlaydi. Sizning tanangizdagi har bir protein ushbu aminokislotalarning bir-biriga bog'langan birikmasidan iborat. har bir, shuningdek, ularni ifodalash uchun ishlatiladigan notation haqida bir oz ma'lumot berish.

    Umuman olganda, bu yigirmata aminokislotalarni ikki guruhga bo'lish mumkin: muhim va muhim bo'lmagan. Muhim bo'lmagan aminokislotalar - bu inson tanasi sintez qilish qobiliyatiga ega bo'lgan aminokislotalar, muhim aminokislotalar esa dietadan olinishi kerak. Muhim bo'lmagan aminokislotalar - alanin, arginin, asparagin, aspartat, sistein, glutamik kislota, glutamin, glitsin, prolin, serin va tirozin, ulardan ba'zilari "shartli ravishda muhim" deb ham atalishi mumkin, ya'ni ular zarur bo'lishi mumkin. kasallik paytida yoki sog'liq muammolari natijasida dieta. Ushbu kichik toifaga arginin, glitsin, sistein, tirozin, prolin va glutamin kiradi. Muhim aminokislotalar histidin, izolösin, leysin, lizin, metionin, fenilalanin, treonin, triptofan va valindir.

    Aminokislotalar organizm tomonidan yog 'va kraxmal bilan bir xil tarzda saqlanishi mumkin emas, shuning uchun biz sintez qila olmaydiganlarni dietamizdan olishimiz juda muhimdir. Aks holda, organizmdagi oqsil sintezining inhibisyoniga olib kelishi mumkin, bu esa keyingi sog'liq uchun keng ko'lamli ta'sirga olib kelishi mumkin. Aminokislotalar ratsiondagi oqsilning parchalanishidan olinadi, shuning uchun protein etishmasligi dietasi muhim aminokislotalarni iste'mol qilishga ta'sir qilishi mumkin.

    Aminokislotalar tomonidan hosil bo'lgan oqsillar nihoyatda katta molekulalar bo'lishi mumkinligi sababli, ularning kimyoviy tuzilishini kichikroq molekulalar uchun qilganimiz kabi aniqlash juda ko'p vaqt talab qiladi va qiyin. Shu sababli, oqsillarni tashkil etuvchi keng tarqalgan aminokislotalarga oqsillarning tuzilishini tasvirlashni osonlashtirish uchun molekulalarda paydo bo'lganda ularni ifodalash uchun ishlatilishi mumkin bo'lgan kodlar beriladi. Uch harfli va bitta harfli kodlar mavjud bo'lib, bir harfli kodlarning kelib chiqishi kompyuterlar eskiroq va murakkabroq bo'lganida, oqsillarni tashkil etuvchi aminokislotalar ketma-ketligini tasvirlash uchun foydalaniladigan fayllar hajmini kamaytirish talabi bilan bog'liq edi. Ushbu bir harfli kodlar bioinformatika sohasida kashshof hisoblangan doktor Margaret Okli Dayhoff tomonidan ishlab chiqilgan (biologik ma'lumotlarni saqlash, tartibga solish va sharhlash uchun dasturiy ta'minot va axborot tizimlaridan foydalanish).

    Ushbu jadvalda inson genetik kodi to'g'ridan-to'g'ri kodlaydigan 20 ta aminokislota ko'rsatilgan bo'lsa-da, boshqa aminokislotalarni 21-o'ringa qo'yish kerakmi yoki yo'qmi degan bahs-munozaralar mavjud. Selenotsistein aminokislota bo'lib, bu erda tasvirlangan 20 dan farqli o'laroq, oz sonli inson oqsillarida mavjud, ammo u to'g'ridan-to'g'ri emas, balki maxsus tarzda kodlangan. Yana bir narsa, pirolizin, xuddi shunday kodlangan va 22-aminokislota hisoblanadi.

    (Izoh: Aminokislotalarni boʻlishning yana bir usuli ularning fizik xususiyatlariga asoslanadi. Aminokislotalarni tasniflashning ushbu usulining qisqacha mazmunini bu yerda koʻrishingiz mumkin.)

    Siz shuningdek, har bir aminokislota uchun DNK kodonlarini, shuningdek, fiziologik (tana) pH dagi tuzilmalarni ko'rsatadigan grafik versiyasini yuklab olishingiz mumkin.


    Nima uchun aminokislotalar kislotali va asosiy aminokislotalarning funktsional guruhlarida bog'lanmaydi? - Biologiya

    aminokislotalarni KIRISH

    Ushbu sahifa biologik ahamiyatga ega bo'lgan 2-aminokislotalarga e'tibor qaratib, aminokislotalar nima ekanligini tushuntiradi. Ularning eruvchanligi va erish nuqtalari kabi oddiy fizik xossalarini batafsil ko'rib chiqadi.

    Aminokislotalar ular aytganidek! Ular -NH aminokislotalarini o'z ichiga olgan birikmalardir2, va karboksilik kislota guruhi, -COOH.

    Biologik ahamiyatga ega aminokislotalar -COOH guruhiga qo'shni uglerod atomiga biriktirilgan aminokislotalarga ega. Ular sifatida tanilgan 2-aminokislotalar. Ular (bir oz chalkashlik bilan) sifatida ham tanilgan alfa-aminokislotalar. Bular biz diqqatimizni qaratadigan narsalardir.

    Ushbu aminokislotalarning eng oddiy ikkitasi 2-aminoetanik kislota va 2-aminopropanoik kislotadir.

    Bu kabi molekulalarning biologik ahamiyati tufayli ular odatda an'anaviy biokimyoviy nomlari bilan tanilgan.

    Masalan, 2-aminoetanik kislota odatda deyiladi glitsin, va 2-aminopropanoik kislota odatda ma'lum alanin.

    2-aminokislotalarning umumiy formulasi:

    . . . Bu erda "R" -OH, -SH, boshqa amin yoki karboksilik kislota guruhlari va boshqalar kabi boshqa faol guruhlarni o'z ichiga olgan juda murakkab guruh bo'lishi mumkin. Bu, albatta, oddiy uglevodorod guruhi bo'lishi shart emas!

    Eslatma: To'liq aniqlik uchun 20 ta biologik muhim aminokislotalardan biri (prolin) biroz boshqacha tuzilishga ega. "R" guruhi aylana shaklida egilib, vodorodlardan birining o'rniga yana azotga yopishadi. Bu asorat aslida birikmaning kimyosida unchalik katta farq qilmaydi - azot hali ham boshqa aminokislotalarda bo'lgani kabi o'zini tutadi. Bu kirish darajasida kimyo maqsadlari uchun tashvishlanishingiz kerak bo'lgan narsa emas.

    Aminokislotalar hayratlanarli darajada yuqori erish nuqtalariga ega bo'lgan kristalli qattiq moddalardir. Erish nuqtalarini aniq belgilash qiyin, chunki aminokislotalar erishdan oldin parchalanadi. Parchalanish va erish odatda 200 - 300 ° C oralig'ida bo'ladi.

    Molekulalarning kattaligi uchun bu juda yuqori. G'ayrioddiy narsa yuz berayotgan bo'lishi kerak.

    Agar aminokislotalarning umumiy tuzilishiga yana bir marta nazar tashlasangiz, unda ham asosiy amin guruhi, ham kislotali karboksilik kislotalar guruhi borligini ko'rasiz.

    Vodorod ionining -COOH guruhidan -NH ga ichki o'tishi mavjud2 manfiy va musbat zaryadli ion qoldirish uchun guruh.

    Bu a deyiladi zwitterion.

    Tsvitterion - bu umumiy elektr zaryadiga ega bo'lmagan, lekin musbat va manfiy zaryadlangan alohida qismlarni o'z ichiga olgan birikma.

    Bu aminokislotalar hatto qattiq holatda ham mavjud bo'lgan shakldir. Siz kutgan zaifroq vodorod aloqalari va boshqa molekulalararo kuchlar o'rniga, sizda bir ion va uning qo'shnilari o'rtasida ancha kuchli ionli tortishishlar mavjud.

    Ushbu ionli tortishishlar sindirish uchun ko'proq energiya talab qiladi va shuning uchun aminokislotalar molekulalarning kattaligi uchun yuqori erish nuqtalariga ega.

    Aminokislotalar odatda suvda eriydi va uglevodorodlar kabi qutbsiz organik erituvchilarda erimaydi.

    Bu yana zvitterionlarning mavjudligini aks ettiradi. Suvda qattiq aminokislotadagi ionlar orasidagi ionli tortishish qutbli suv molekulalari va zvitterionlar orasidagi kuchli tortishish bilan almashtiriladi. Bu suvda eriydigan boshqa har qanday ionli moddalar bilan bir xil.

    Suvdagi eruvchanlik darajasi "R" guruhining kattaligi va tabiatiga qarab o'zgaradi.

    Eslatma: Ushbu nuqtada men odatda turli xil aminokislotalarning eruvchanligining haqiqiy qiymatlarini ularning tuzilishi bilan bog'lashga harakat qilaman. Afsuski, men ega bo'lgan eruvchanlik qiymatlaridan (va ular to'g'ri ekanligiga ishonchim komil emas), men hech qanday aniq naqsh topa olmayapman - aslida, juda g'alati holatlar mavjud.

    Uglevodorodlar kabi qutbsiz organik erituvchilarda eruvchanlikning yo'qligi erituvchi molekulalari va zvitterionlar o'rtasidagi tortishishning yo'qligi bilan bog'liq. Erituvchi va aminokislotalar o'rtasida kuchli tortishish bo'lmasa, ion panjarasini ajratish uchun etarli energiya ajralib chiqmaydi.

    Agar siz aminokislotalarning umumiy formulasini yana bir bor ko'rib chiqsangiz, strukturaning markazidagi uglerod (glisin, 2-aminoetanik kislotadan tashqari) to'rt xil guruhga biriktirilganligini ko'rasiz. Glitsinda "R" guruhi boshqa vodorod atomidir.

    Agar siz oddiyroq strukturaning o'rniga zvitterionning tuzilishini chizsangiz, bu xuddi shunday bo'ladi.

    Bir xil uglerod atomiga biriktirilgan ushbu to'rt xil guruh tufayli aminokislotalar (glisindan tashqari) chiral.

    Muhim: Agar bilmasangiz aynan bu nimani anglatadi, optik izomeriya haqidagi sahifaga ushbu havolaga o'ting. Siz ushbu sahifaning pastki qismida muhokama qilingan aminokislotalarning optik faolligini topasiz, lekin nima bo'layotganini tushunganingizga ishonch hosil qilish uchun butun sahifani o'qing.

    Ushbu sahifaga qaytish uchun brauzeringizdagi BACK tugmasini bosing.

    Simmetriya tekisligining yo'qligi aminokislotalarning ikkita stereoizomerlari (glisindan tashqari) bo'lishini anglatadi - biri ikkinchisining ustiga qo'yilmaydigan oyna tasviri.

    Umumiy 2-aminokislota uchun izomerlar:

    Eslatma: Agar siz turli xil bog'lanish belgilari nimani anglatishini bilmasangiz, bu qadar uzoqqa bormasligingiz kerak edi! Yuqoridagi havola orqali optik izomeriya haqidagi sahifaga o'ting. Ushbu sahifani o'qing va organik molekulalarni chizish uchun ushbu sahifadagi keyingi havolaga o'ting.

    Ushbu sahifaga qaytish uchun brauzeringizdagi BACK tugmasini bosing.

    Barcha tabiiy aminokislotalar ushbu diagrammada o'ng tomonli tuzilishga ega. Bu "L-" konfiguratsiyasi sifatida tanilgan. Ikkinchisi "D-" konfiguratsiyasi sifatida tanilgan.

    Buyuk Britaniyaning A darajasidagi kimyo maqsadlari uchun buni bilishingiz shart emas, lekin agar sizni qiziqtirsa, oxirgi diagrammada o'ng tomondagi tuzilishga yuqoridan pastga qarayotganingizni tasavvur qilib, L-konfiguratsiyasini tanib olishingiz mumkin - boshqacha qilib aytganda, sizga eng yaqin vodorod atomi bilan. Agar siz boshqa guruhlarni soat yo'nalishi bo'yicha o'qisangiz, siz MAKORA so'zini olasiz.

    Ogohlantirish: MAKSORN so'ziga asoslanib, buni amalga oshirishning turli xil usullari mavjud, ammo molekulaga boshqa nuqtai nazardan qarash, bu L-formasi uchun MAKSORNni soat miliga qarshi emas, balki soat sohasi farqli ravishda qo'llash kerakligini anglatishi mumkin.

    Agar siz allaqachon boshqa qoidani o'rgangan bo'lsangiz, unga rioya qiling. Agar siz A darajasidagi (yoki unga tenglashtirilgan) kimyo talabasi bo'lsangiz, imtihonchilaringiz nimani kutayotganini (agar biror narsa bo'lsa) bilib oling va buni bilib oling. Agar bu haqda bilishingiz shart bo'lmasa, uni unuting!

    Siz strukturaga qarab, bu izomer polarizatsiyalangan tekislik nurining qutblanish tekisligini soat yo'nalishi bo'yicha yoki soat miliga teskari yo'nalishda aylantirishini ayta olmaysiz. Barcha tabiiy aminokislotalar bir xil L konfiguratsiyasiga ega, ammo ular tekislikni soat yo'nalishi bo'yicha (+) va aksincha (-) aylantiradigan misollarni o'z ichiga oladi.

    Tabiiy tizimlar faqat aminokislotalar kabi optik faol moddaning optik izomerlaridan (enantiomerlaridan) biri bilan ishlashi juda keng tarqalgan. Nima uchun bunday bo'lishi mumkinligini tushunish unchalik qiyin emas. Molekulalar turli guruhlarning turli fazoviy joylashuviga ega bo'lganligi sababli, ulardan faqat bittasi ular bilan ishlaydigan fermentlarning faol joylariga to'g'ri joylashishi mumkin.

    Tushunishingizni tekshirish uchun savollar

    Agar bu birinchi savollar to'plami bo'lsa, boshlashdan oldin kirish sahifasini o'qing. Keyinchalik bu yerga qaytish uchun brauzeringizdagi ORQA TUGMASIdan foydalanishingiz kerak bo'ladi.


    8 ta muhim aminokislotalar

    Muhim narsalarni tushunish va ularni dietangizda optimallashtirishga urinish har qanday bodibilding uchun asosiy bilim bo'lishi kerak.

    Aminokislotalarning to'liq spektrini va optimal salomatlikni faqat protein iste'mol qilishni ushbu 8 aminokislotaga moslashtirish orqali olish mumkin. Shunday qilib, hatto bepul shakllar bilan to'ldirishni o'ylamasangiz ham, hech bo'lmaganda ushbu keyingi 8 paragrafni ko'rib chiqing va o'rganing.

    Histidin

    Inson tanasida histidin barcha turdagi to'qimalarning o'sishi va tiklanishi uchun zarurdir. U oligo-dendrositlar deb ataladigan glial nerv hujayralarini saqlash va ishlab chiqarishda muhim rol o'ynaydi, ular miyelin deb ataladigan himoya niqobini hosil qilish uchun nervlarni o'rab oladi.

    Bu miya va orqa miyada jiddiy nuqsonlarga olib kelishi mumkin bo'lgan kutilmagan impulslarning oldini oladi. Go'yo u etarli ishlamagandek, histidin ham qizil, ham oq qon hujayralari ishlab chiqaruvchisi.

    Shuningdek, u radiatsiyadan himoya qilish va tanadan ortiqcha og'ir metallarni (masalan, temir) olib tashlashga yordam beradi. Oshqozonda u ovqat hazm qilishni tezlashtiradigan va yaxshilaydigan me'da shirasini ishlab chiqaradi, shuning uchun u hazmsizlik va oshqozon-ichak kasalliklariga qarshi kurashda foydali vositadir.

    Bu allergik reaktsiyalarga javob sifatida immunitet tizimi tomonidan chiqariladigan muhim bo'lmagan aminokislota gistaminining kashshofidir. Bu, shuningdek, so'nggi tadqiqotlarda uzoqroq orgazm va bu sohada biroz muammoga duch kelganlar uchun jinsiy zavqlanishni yaxshilash bilan bog'liq.

    Bodibilding haqida qisqacha ma'lumot

    Bodibildingchilar uchun foydalaning: Minimal, faqat ovqat hazm qilishni yaxshilashda

    Dozaj: Kuniga kamida 1000 mg, ammo tavsiya etilgan vazn tana vazniga kuniga 8-10 mg. Ehtimol, siz dietangizdan kamida ikki yoki uch marta olasiz.

    Dozani oshirib yuborish: Gistidinni haddan tashqari ko'p iste'mol qilish stressga va tashvish va shizofreniya kabi ruhiy kasalliklarning kuchayishiga olib kelishi mumkin.

    Tibbiy maqsadlarda foydalanish: Artrit va asab karliklarini davolashda ishlatiladi.

    Manbalar: Sut, go'sht, parrandachilik, baliq, shuningdek guruch, bug'doy va javdarda mavjud.

    Kamchilik: Noma'lum.

    Foydalanish: Yaxshi hazm qilish - Manbalar: Sut, go'sht, baliq, guruch, bug'doy va javdar

    Lizin

    L-lizin o'sish va rivojlanish uchun juda muhim bo'lgan aminokislotalardan biridir. U organizmda kaltsiyni so'rilishi uchun ishlatiladi, bu suyak va mushaklarning o'sishiga, shuningdek, energiya ishlatish uchun yog'larning mobilizatsiyasiga olib keladi.

    Bu azot muvozanatini saqlaydi va haddan tashqari stress va charchoq davrlarida ozg'in tana massasini saqlashga yordam beradi. Shuningdek, u antikorlar, gormonlar (GH, testosteron, insulin, siz aytasiz), fermentlar, kollagen ishlab chiqarish va gistidin va ko'pgina muhim aminokislotalarga o'xshash shikastlangan to'qimalarni tiklash uchun kerak.

    Uni saqlab qolishdan tashqari, u yangi mushak oqsilini yaratishga ham yordam beradi. Va yurak-qon tomir foydalari sog'lom qon tomirlarini saqlashni o'z ichiga oladi.

    Bodibilding haqida qisqacha ma'lumot

    Bodibildingchilar uchun foydalaning: Mushak oqsilini saqlash va ishlab chiqarish bilan bir qatorda, lizin charchoq va ortiqcha mashg'ulotlarga qarshi kurashish uchun tanani jonlantirishda rol o'ynaydi va u ijobiy azot balansini saqlab, tanada anabolik muhitni yaratadi.

    Dozaj: Oddiy tavsiya tana vazniga 12 mg ni tashkil qiladi, ammo kunlik iste'mol qilish undan oshadi va hatto tana vazniga 1,5 gramm protein qabul qilganda ham, qo'shimcha bir necha mg zarar qilmaydi. Bu sportchi uchun ustuvor aminokislotadir. lekin dozani oshirib yuborishdan ehtiyot bo'ling.

    Dozani oshirib yuborish: LDL xolesterinning ko'payishi, diareya va o't pufagida tosh paydo bo'lishiga olib kelishi mumkin.

    Tibbiy maqsadlarda foydalanish:Sovuq yaralarni davolash va energiya etishmasligi.

    Manbalar: Pishloq, tuxum, sut, go'sht, xamirturush, kartoshka va lima loviya.

    Kamchilik: Fermentlarning buzilishi, energiya etishmasligi, soch to'kilishi (oqsil etishmovchiligi uchun keng tarqalgan), vazn yo'qotish, ishtahaning yo'qligi va konsentratsiyaning yo'qolishiga olib kelishi mumkin.

    Foydalanish: charchoq va ortiqcha mashq qilish bilan kurashadi - Manbalar: pishloq, tuxum, sut, go'sht, xamirturush, kartoshka va loviya loviya

    Fenilalanin

    Fenilalanin, aniqrog'i, dolzarb mavzu edi. Ba'zi odamlar bunga juda yomon munosabatda bo'lishadi va uning mahsulotlarda qo'llanilishi haqida ko'p fikrlar bildirildi. Vaziyat tinchlandi va tadqiqotlar shuni ko'rsatdiki, sog'lom odamlar uchun buning hech qanday zarari yo'q.

    Bu asab tizimini rag'batlantirish orqali kayfiyatni ko'taradi va har qanday sababga ko'ra motivatsiyani saqlab qolish uchun muhim bo'lishi mumkin. U xotiraga yordam beradi va uning hosilasi glutamin bilan birgalikda aqlli vitamin hisoblanadi (ular vitamin emas).

    Bu gipofizning oldingi qismida epinefrin, nor-epinefrin va dofamin darajasini oshiradi. Uchalasi ham asab tizimining optimal ishlashi uchun zarur bo'lgan muhim neyrotransmitterdir. Shuningdek, u quyosh nurida ultrabinafsha nurlarining so'rilishiga yordam beradi, bu esa o'z navbatida kuchli tana gormoni bo'lgan D vitaminining yuqori darajasini beradi.

    Uning asosiy metaboliti tirozin bo'lib, yuqorida aytib o'tilganidek, dopamin va epinefrin darajasini oshiradi. Shuningdek, u aminokislotalar hovuzining eng katta qismini tashkil etuvchi aminokislota glutamin ishlab chiqaruvchilardan biridir.

    Fenilalanin ko'pincha matbuotda yomon o'raladi. U ko'plab alkogolsiz ichimliklarda uglevodsiz tatlandırıcı sifatida ishlatiladi (aspartik kislota, aspartam kabi) va yaqinda ba'zilar miya uchun xavfli ekanligini da'vo qilganda sarlavhalar paydo bo'ldi va keyinchalik u kanserogen xavf bilan bog'liq edi.

    Fenilalaninning zaharli darajasi haqiqatan ham o'limga olib kelishi mumkin, ammo menga ishoning, boshqa hamma narsa ham mumkin. Agar boshingga miltiq qo‘yib, yigirma litr tozalangan suv ichirsam, sen ham o‘lgan bo‘larding. Va bu suv. Tasavvur qiling-a, vitaminlar yoki minerallar qanday yordam berishi mumkin?

    Shunga qaramay, kimdir sizni o'ldirish uchun yerga qo'yilgan vitaminlarni yomon zahar deb bilishiga shubha qilaman. Xo'sh, fenilalanin ham emas. Bu muhim aminokislotadir va ko'pchilik dietologlar dozani oshirib yuborish xavfidan ko'ra sizda etishmovchilik ehtimoli ko'proq ekanligini aytishadi.

    Toksik dozalar kuniga 250-300 gramm proteinni o'z ichiga olgan dietadan o'rtacha 3-4 baravar ko'pdir. Shunday qilib, qo'shimcha dietali kola sizni o'ldirmaydi.

    Bodibilding haqida qisqacha ma'lumot

    Bodibildingchilar uchun foydalaning: Motivatsiya va qo'shimcha D vitamini bilan bir qatorda, fenilalanin mushaklarning maksimal qisqarishi va bo'shashishiga imkon beradigan nervlarni yangilash uchun ishlatiladi. DL shakli ko'pincha chidamlilikni kuchaytiruvchi vosita sifatida to'ldiriladi. Toksiklik darajasi tufayli bu hech qachon uzoq muddatli amalga oshirilmaydi.

    Dozaj: Tavsiya - har bir kilogramm tana vazniga 14 mg. Shubhasiz, siz bundan ko'proq narsani olasiz va men buni oshirishga hojat yo'qligini ko'raman. Ayniqsa, mumkin bo'lgan yon ta'sirlar bilan.

    Dozani oshirib yuborish: Bu homilador ayollar va diabetga chalinganlar tomonidan qabul qilinadigan oqilona qo'shimcha emas. Bu yuqori qon bosimi, bosh og'rig'i, ko'ngil aynishi, yurak muammolari va nervlarning shikastlanishiga olib keladi.

    Tibbiy maqsadlarda foydalanish: Artrit va depressiyani davolash uchun.

    Manbalar: Barcha sut mahsulotlari, bodom, avakado, yong'oq va urug'lar.

    Kamchilik: Bu kamdan-kam uchraydi, lekin agar u paydo bo'lsa, zaiflik, letargiya, jigar shikastlanishi va o'sishning sekinlashishiga olib keladi.

    Foydalanish: mushaklarning maksimal qisqarishi va bo'shashishiga imkon beradi - Manbalar: Sut, bodom, avakado, yong'oq va urug'lar

    Metionin

    Kelajakdagi maqolada ZMA ni muhokama qilganimizda, men bu mavzuga yana bir bor murojaat qilaman, ammo metionin yog'larning parchalanishi va ishlatilishiga yordam beradi, bu esa o'z navbatida yuqori testosteron darajasini beradi.

    Sink bilan birgalikda ZMA o'z ishini shunday qiladi. Bundan tashqari, qon oqimidan ortiqcha yog'ni yo'q qiladi, natijada kamroq potentsial yog' (yog') to'qimalari paydo bo'ladi. Bu ovqat hazm qilish va oshqozon va jigardan og'ir metallarni olib tashlashda kalit hisoblanadi. Bu yaxshi antioksidant, chunki u oltingugurtni osonlik bilan ta'minlaydi, erkin radikallarni faolsizlantiradi va xotirani eslab qolishga yordam beradi.

    Bu jigarni detoksifikatsiya qilish uchun glutation ishlab chiqaradigan aminokislota bo'lgan sisteinning kashshofidir. Bu, shuningdek, energiya ishlab chiqarish va mushaklarning o'sishi uchun zarur bo'lgan tanadagi kreatin monohidratini ishlab chiqarish uchun zarur bo'lgan uchta aminokislotadan biridir.

    Bodibilding haqida qisqacha ma'lumot

    Bodibildingchilar uchun foydalaning: Yog 'almashinuvi, yaxshiroq hazm qilish va oksidlanishga qarshi xususiyatlar uni qimmatli birikmaga aylantiradi.

    Dozaj: Tana vaznining kilogrammiga 12 mg. If you think it may be a good idea to supplement this, you may as well invest in some ZMA. The supplement is cost-effective and yields higher results than just Methionine.

    Overdosing: None, except in case of a shortage of B-Vitamins, in which case you are an easy target for arteriosclerosis.

    Medical Uses: Used to treat depression, arthritis and liver disease.

    Manbalar: Meat, fish, beans, eggs, garlic, lentils, onions, yogurt and seeds.

    Kamchilik: Causes dementia, fatty liver, slow growth, weakness, skin lesions and edema.

    BCAAs

    Branched-chain amino acids are held in high regard in bodybuilding circles and justly so. They are the three most important amino acids in the manufacture, maintenance and repair of muscle-tissue. All three exert a strong synergistic effect.

    Using just Valine or Iso-leucine does little as far as anabolics is concerned but both, when dosed in the right amounts, enhance the effect of the all-important Leucine. As with certain other supplements, the relative dose is more important than the overall dose.

    It is believed that a 2-1-2 equilibrium in Leucine/Iso-leucine/Valine dosing yields the best results. The dosages listed are the FDA recommendations for taking the individual BCAA's. BCAAs are used medically to treat headaches, dizziness, fatigue, depression and irritability as a result of protein deficiency.

    BCAAs are always best used together. A little useful stack advice: BCAAs stack well with B-complex vitamins.

    Leysin

    Leucine, the strongest of the BCAAs, is responsible for the regulation of blood-sugar levels, the growth and repair of tissues in skin, bones and of course skeletal muscle.

    It's a strong potentiator to Human Growth Hormone (HGH). It helps in healing wounds, regulating energy, and assists in the preventing the breakdown of muscle tissue.

    Bodybuilder Summary

    Use To Bodybuilders: Leucine may be one of the strongest natural anabolic agents in the world. It will not give you amazing results, however, simply because you are already taking in quite large amounts of it.

    Dosage: 16 mg per kilo of bodyweight.

    Overdosing: Unknown, may increase ammonia.

    Medical Uses: Prevention of muscle-wasting in states of deprivation.

    Manbalar: Found in nearly all protein sources, including brown rice, beans, nuts, and whole wheat.

    Kamchilik: Noma'lum.

    Uses: Natural anabolic agent — Sources: All protein sources including brown rice, beans, nuts, and whole wheat

    Izoleysin

    Very similar to leucine in most every way. Isoleucine promotes muscle recovery, regulates the blood-sugar levels and stimulates HGH release. But isoleucine holds its own in terms of wound healing.

    It helps in the formation of hemoglobin and is strongly involved in the formation of blood-clots, the body's primary defense against infection through open wounds.

    Bodybuilder Summary

    Use To Bodybuilders: Of similar importance as leucine, Very important as part of the BCAA stack.

    Dosage: 10-12 mg per kilo of bodyweight.

    Overdosing: Causes elevated urination. No serious problems. May become serious if you have kidney or liver disease.

    Medical Uses: Wound healing.

    Manbalar: Chicken, cashews, fish, almonds, eggs, lentils, liver, meat.

    Kamchilik: Noma'lum.

    Promotes muscle recovery — Sources: Chicken, cashews, fish, almonds, eggs, lentils, liver, and meat

    Valin

    Valine helps the repair and growth of muscle tissue, as commonly attributed to BCAAs. It maintains the nitrogen balance and preserves the use of glucose.

    Bodybuilder Summary

    Use To Bodybuilders: In combination with Isoleucine and Leucine.

    Dosage: 16 mg per kilo of bodyweight.

    Overdosing: Crawling sensation in the skin is common, hallucination, may be hazardous to people with kidney and liver disease.

    Medical Uses: None, not separately.

    Manbalar: Dairy, meat, grain, mushrooms, soy, peanuts.

    Kamchilik: Leads to MSUD.

    Uses: Promotes repair and growth of muscle tissue — Sources: Dairy, meat, mushrooms, soy, and peanuts

    Treonin

    An essential amino acid that is not manufactured within the body, ever. Since its main sources are animal (dairy and meat) this doesn't bode well to vegans. It's found in heart, skeletal muscle and nerve tissue in the central nervous system.

    Threonine (reminds me of that chick on "Star Trek: Voyager") is used to form the body's two most important binding substances, collagen and elastin. It is also essential to maintain proper protein balance.

    Threonine is involved in liver functioning, lipotropic functions (when combined with aspartic acid and methionine) and in the maintenance of the immune system by helping in the production of antibodies and promoting growth and activity of the thymus.

    But perhaps its most useful property of all is that it allows better absorption of other nutrients, so protein sources containing threonine are more bio-available than others.

    Bodybuilder Summary

    Use To Bodybuilders: Absorption of protein, maintenance of muscle and important to good health.

    Dosage: 8 mg per kilo of bodyweight, generally advised in amounts of 100-500 mg when supplemented.

    Overdosing: Not known.

    Medical Uses: Treatment for mental health.

    Manbalar: Meat, dairy, and eggs.

    Kamchilik: Irritability and being difficult, nothing severe. Less immunity against disease.

    Uses: Absorption of protein — Sources: Meat, dairy, and eggs


    The alphabet soup of life

    For many researchers, studying the chemical origins of life is a side project – it’s what they do in between their grant-funded work on the causes and cure of human disease. But understanding evolution at the chemical level is their passion, even when funding is sparse. How chemistry could have brought us to complex life poses many open questions. One fundamental question is why life is based on a set 20 amino acids. Why 20 and not 10 or 30? And why those particular 20? Over the last few decades, the passionate chemists and molecular biologists who can’t leave these questions alone have started piecing together some convincing explanations.

    From alanine (A) to tyrosine (Y), 20 ‘proteinogenic’ amino acids, each abbreviated to a different initial, make up the alphabet soup of life. They are the building blocks for proteins, biology’s workhorse macromolecules that provide structure and function in all organisms. But why amino acids? Bernd Moosmann, an expert in redox medicine at the Johannes Gutenberg University of Mainz in Germany suggests the first amino acids were used to anchor membranes to RNA structures: ‘You can see this even in modern life: DNA and RNA in bacteria and mitochondria are always attached from the inside to a membrane.’ Most researcher think this would have been occurring at least 4 billion years ago in an ‘RNA world’, where RNA molecules were the first self-replicators, as well as performing the catalytic role that proteins play today.

    Source: © Royal Society of Chemistry

    How the proteinogenic amino acids came to be on earth is another crucial question. The famous Miller–Urey experiment from 1952 showed that with electric sparks simulating lightning, simple compounds like water, methane, ammonia and hydrogen would form well over 20 different amino acids. 1 They are also found in meteorites: analysis of the Murichison meteorite, which landed in Australia in 1969, found at least 86 amino acids, substituent chains of up to nine carbon atoms and dicarboxyl and diamino functional groups. 2 Perhaps these generally simple and readily available amino acids were the first to be press-ganged into life?

    Andrew Doig, a chemical biologist at the University of Manchester in the UK, has been thinking about the chemistry of evolution, when not carrying out his research into Alzheimer’s disease. He has a different take on the question: ‘[The proteinogenic amino acids] were chosen in the RNA world, where there had been life and metabolism for millions of years, already generating a vast number of organic molecules.’ If amino acids were a product of RNA metabolism this would hugely increase their concentrations in the environment, he argues.

    But the selection of the 20 amino acids used in biology is clearly linked to the development of proteins. By polymerising amino acids in long polypeptide chains, proteins could fold into soluble structures with close-packed cores and ordered binding pockets. The arrival of proteins and the eventual adoption of the standard 20 amino acids was likely to have been a big evolutionary step.

    Source: Meteorite image (left) courtesy of Argonne National Lab

    Plenty of amino acids (right) were found on the Murchison meteorite (left)

    But according to Doig, this is all speculation. ‘We have no direct evidence at all.’ What we do know from comparing genomes of organisms today is that by 3.5–3.8 billion years ago our common ancestor – known as the last universal common ancestor – was using the 20 amino acids common to all living things.

    A frozen accident?

    So why that particular set of 20 amino acids rather than any other? ‘The obvious missing thing is the ability to do redox reactions,’ explains Doig. ‘They weren’t selected for ability to do catalysis directly.’ Today, proteins form enzymes for biological catalysis, but the first biological catalysts in the RNA world were probably what we now call co-factors – metal ions or non-protein organic molecules (coenzymes) that assist enzymes during the catalysis of reactions and are often made from vitamins.

    The 20 amino acids have a range of properties…

    There has been a tendency to see the choice of the 20 amino acids as arbitrary – as in the ‘frozen accident theory’ proposed by British molecular biologist Francis Crick in the 1960s, which suggested a different group of 20 would be just as good. ‘I kept on reading this and realising this wasn’t right,’ says Doig. This spurred him on to put down his thoughts in a recent paper where he argues there are reasons for the selection of every amino acid making them a near ideal group. 3 The factors he took into account included each amino acid’s component atoms, functional groups and biosynthetic cost.

    Forming soluble, stable protein structures with close‐packed cores and ordered binding pockets needed the variety of amino acids we see today, explains Doig. Multiple hydrophobic proteins are needed. ‘The core of a protein is a 3D jigsaw puzzle – if you have lots of different hydrophobic amino acids it gives you more options to build a core without any gaps.’

    The fact that the hydrophobic amino acids tend to have branched side chains can also be explained. Inside the protein core, the molecule is no longer able to rotate and loses some of its associated entropy. ‘If you have branched amino acids like valine, leucine and isoleucine, you lose less entropy when you bury them, so evolution has chosen hydrophobic amino acids not just because they are hydrophobic but also because they are branched,’ explains Doig. ‘If you want amino acids to go in the core of a protein you make it branched and hydrophobic, if you want it to be on the surface then you make it a straight chain and polar like arginine and glutamic acid.’

    Chemical space

    Stephen Freeland, an astrobiologist at the University of Maryland in the US, has come up with a method to show that the amino acids adopted by biology were not chosen randomly. He borrowed the idea of chemical space from drug discovery, where molecules are plotted in 3D space to help discover gaps that might reap novel drug molecules. The three parameters investigated by Freeland and his team were size, charge and hydrophobicity. ‘They are not perfect,’ admits Freeland, ‘but as rough proxies of what amino acids do and why they do it, those three are pretty good.’ Hydrophobicity obviously plays a pivotal role in how proteins fold, charge is important in reactions and active sites, and size was just intuitive, Freeland says.

    ‘We found that the set that is used by biology has a number of surprisingly non-random properties that stand out very clearly,’ says Freeland. The amino acids were widely distributed through their chemical space, but also showed an evenness within that distribution – as if trying to cover as many different property sets as possible. 4 ‘What we find with [proteinogenic] amino acids is the moment you build in both of those two factors [hydrophobicity and charge] , just about every test you can throw at them says they are non-random – not only do they cover a good range but they are not clumped to extremes.’

    So if this non-random set of amino acids was chosen for good reason, is it possible to create an order in which they were incorporated into biology? ‘There is a consensus now that they didn’t all arrive at once, which to my mind is overwhelming,’ says Freeland. An attempt to come up with a comprehensive order was made by Israeli molecular biophysicist Edward Trifonov, now at the Institute of Evolution at the University of Haifa. Trifonov discovered multiple novel codes in DNA and in the early 2000s turned his attention to amino acids.

    Placing the chemically simplest amino acids first might seem obvious, but Trifonov took this further. He looked at multiple criteria, including the energetic cost of their synthesis, the type of transfer-RNA molecules used to transport them and the number of codons (the sequence of three RNA nucleotides that corresponds with a specific amino acid) used in protein synthesis amino acids with multiple codons are probably older than those with one. He averaged the data and proposed a temporal order starting with alanine and glycine. 5

    Freeland also looked at how patterns might vary with amino acids assumed to be adopted earlier and later. Using the first 10 alone in chemical space, he found non-random properties in contrast to an examination of all the possible amino acids available on the prebiotic earth (from Miller–Urey or meteorites). Then he added in the complete set of 20. ‘The later ones expand the chemical space of the earlies in ways that maximise range and evenness, and for my money the most interesting single thing is they seem to plug the region of chemical space that was underpopulated, between where the earlies sit and where dimers of the earlies would sit,’ he says. ‘It just makes perfect sense, that this is where you would plug.’

    Oxygen expands the code

    We certainly know proteins can be made with a much smaller set of amino acids. A Japanese group headed by Satoshi Akanuma at Waseda University recently showed that a 13 amino acid alphabet can create folded, soluble, stable and catalytically active ‘proteins’, albeit not as active or stable as the parent proteins on which they were based. 6 So what might have prompted the addition of extra amino acids? According to Moosmann, molecular oxygen forced life to incorporate the last six novel amino acids.

    The presumed last six amino acids (histidine, phenylalanine, cysteine, methionine, tryptophan and tyrosine) are all chemically ‘softer’ – they are strongly polarizable and bond covalently. ‘It’s most likely adaptive and not a coincidence or a drift,’ says Moosmann. The idea came to Moosmann during studies on mouse brain tissue (his ‘day job’ involves research into neurodegenerative diseases). He noticed that some amino acids were much more prone to oxidative degradation – those thought to have been adopted later.

    The introduction of oxygen to the atmosphere meant new amino acids were needed

    If these amino acids were added to biology for their redox activity he had a hunch that these adaptations were linked to increases in molecular oxygen levels on earth. Oxygen is thought to have become part of the earth’s environment around 2.5 billion years ago in what is known as the ‘great oxidation event’, but Moosmann says that the basic first origin of local low-dose oxygen production is probably older. According to recent research on the evolution of the enzymes involved in photosynthesis, Tanai Cardona at Imperial College London in the UK has suggested the origin of oxygenic photosynthesis to have been 3.6 billion years ago. 7

    He decided to probe further by looking at the Homo–Lumo gaps for all biological amino acids. The energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital predicts the reactivity of a compound with respect to electron transfer. 8 ‘The Homo–Lumo gaps [of all 20 amino acids] had a pattern, just falling at the very point (number 14) when “adaptive” properties came in, and this coincidence is probably not a coincidence!’

    The substantially smaller gaps found for the later amino acids suggests their primary function was to undergo redox reactions and Moosmann argues this was needed in an environment where oxygen free-radicals could form, which are particularly destructive to lipids. The ‘softer’ and more redox-active amino acids were capable of protecting cells: ‘These [new amino acid] species could maintain the lipid bilayer integrity in the presence of the rising oxygen concentrations or in the presence of chemical influences which tend to attack or degrade unsaturated fatty acids,’ says Moosmann. ‘For the last three [methionine, tryptophan and tyrosine] there is overwhelming evidence for a response to oxygen.’

    One question this then raises is whether our last universal common ancestor contained the full suite of amino acids. A 2016 study identified a set of 355 genes inferred to have been present in the organism that has become known as Luca. 9 Moosman says the date for Luca has been placed between 3.7 and 2.9 billion years ago, so it is possible oxygen was available. ‘The consequence of this is indeed that Luca (if it ever existed) had fewer than 20 amino acids.’ He suggests that later genetic code additions could have been distributed laterally to all modern lines: ‘My best guess is that Luca had 17–18 AAs, lacking methionine and tryptophan and perhaps tyrosine.’

    Why stop at 20?

    Adaptation to an oxygenated world may explain the expansion of the code to 20 amino acids, but why stop there? ‘I would say, look what 20 can do,’ says Freeland. ‘Apparently 20 is good enough for almost every living organism to have adapted to an unimaginable number of habitats over the entire history of life.’

    In fact there are at least two additional amino acids used in organisms, although only one of these is found in human proteins – the selenium-containing selenocysteine. It is found in the active sites of 25 human proteins, but is incorporated by a more complex mechanism than normal protein synthesis. ‘This shows that the process had not stopped, it reached a point where incorporating new amino acids is extremely hard,’ says Lluis Ribas, a molecular biologist at the Institute for Research in Biomedicine, Barcelona, Spain. ‘If you want to do it then you need to find very original solutions.’

    The limitation is in the recognition of the tRNA

    To answer ‘Why 20?’, Riblas has taken a close look at the protein synthesis mechanism – translation. The process is carried out in the cell’s ribosome, a very large complex of RNA and protein molecules. Each amino acid is carried by a bespoke transfer RNA (tRNA) molecule, attached through a hydroxyl group to form an ester. This then reacts with the terminal amino acid of the growing protein chain. The correct amino acid sequence is translated from messenger RNA molecules through Watson–Crick base-pairing with the tRNA molecules. Each tRNA contains a sequences of three bases specific to one of the 20 amino acids – a codon.

    Given each amino acid is coded by a sequence of three bases, you might assume there would be 64 possible combinations (of the four possible bases). While three codons are used as instructions to stop protein synthesis, that still leaves 61 – so why stop at 20 unique amino acids? ‘The limitation is in the recognition of the tRNA.’ Ribas says. Each tRNA molecule has a well-defined tertiary structure that is recognized by the enzyme aminoacyl tRNA synthetase, which adds the correct amino acid. From studying tRNA structures, Ribas concluded the problem is finding ways to make new tRNA molecules that could recognise a new amino acid without picking up existing ones. 10 The possible structures are limited as they must also fit with the existing protein translation machinery.

    ‘It’s like if you have a very simple kind of lock where you could only change three or four pins, you come to a point where you wouldn’t be able to make new keys because a new key will open a lock you have already used and that defeats the purpose,’ he explains. The point where nature was unable to create new unique tRNAs that would not be mistaken for others seems to have been at 20 amino acids. In modern biology this allows most amino acids to be coded by more than one codon – the redundancy helping more accurate translation (amino-acid incorporation mistakes are estimated to occur once in 1000 to 10,000 codons).

    Expanding the amino acid code

    Ribas says his work also has implication for synthetic biologists who are trying to take the genetic code a step further by incorporating unnatural amino acids and perhaps one day improving on nature. In 2011 a team including Harvard synthetic biologist George Church removed one of the three stop codons from E. coli bacteria so it could be replaced with an alternative non-proteinogenic amino acid, and other labs have incorporated such amino acids into proteins.

    Evolutionary theory tell us that the set that we have got is a microcosm of what’s possible

    But Ribas isn’t sure it will be that this will be a successful strategy for synthetic biologists. ‘If you try to develop a system in vivo for the generation of proteins with unnatural amino acids, it’s not very effective, the efficiency is low, and often you have specificity problems,’ he says. Ribas puts this down to the difficulty in creating new tRNA molecules within the current protein translation machinery. ‘I don’t think there is any way around it, [without] extensive remodelling of the whole machinery’ although, he adds, this is something currently being done.

    Even if it becomes possible, Freeland thinks there will be few advantages. ‘Everything in evolutionary theory tell us that the set that we have got is a microcosm of what’s possible.’ Whether expanding the amino acid repertoire of life will turn out to have useful applications remains to be seen, but there is now plenty of evidence that life’s 20 amino acids were well chosen and not a ’frozen accident’.

    But Freeland cautions against an understanding that looks to neatly order chemical evolution. The chances are it was once much messier, with many different types of molecules and mechanisms involved that may have now been replaced. ‘It’s so tempting to work your way up from nothing to something, because that’s what happens when a chemist sits down with a beaker of distilled water and tries to make a reaction happen – but that isn’t what’s happening in the universe, the universe is full of messy chemistry.’

    Rachel Brazil is a science writer based in London, UK

    Ma'lumotnomalar

    1 A P Johnson va boshqalar, Fan, 2008, 322, 404 (DOI: 10.1126/science.1161527)

    2 T Koga and H Naraoka, Sci. Rep., 2017, 7, 636 (DOI: 10.1038/s41598-017-00693-9)

    3 A Doig, FEBS J., 2016, 284, 1296 (DOI: 10.1111/febs.13982)

    4 M A Ilardo and S J Freeland, J. Syst. Kimyo., 2014, 5, 1 (DOI: 10.1186/1759-2208-5-1)

    5 E N Trifonov, J. Biomol. Tarkibi. Dyn., 2004, 22, 1 (DOI: 10.1080/07391102.2004.10506975)

    6 R Shibue va boshqalar, Sci. Rep., 2018, 8, 1227 (DOI: 10.1038/s41598-018-19561-1)

    7 T Cardona, Heliyon, 2018, 4, e00548 (DOI: 10.1016/j.heliyon.2018.e00548)

    8 M Granold va boshqalar, Proc. Natl akad. Sci. AQSH, 2018, 115, 41 (DOI: 10.1073/pnas.1717100115)

    9 M C Weiss va boshqalar, Nat. Mikrobiol., 2016, 1, 16116 (DOI: 10.1038/nmicrobiol.2016.116)

    10 A Saint-Léger va boshqalar, Sci. Adv., 2016, 2, e1501860 (DOI: 10.1126/sciadv.1501860)


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