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8.16C: Opisthokonts - Hayvonlar va zamburug'lar - Biologiya

8.16C: Opisthokonts - Hayvonlar va zamburug'lar - Biologiya


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O'quv maqsadlari

  • Opistkokontsni tavsiflang

Opisthokonts yoki "zamburug'lar/metazoa guruhi" eukariotlarning keng guruhi bo'lib, hayvonlar va zamburug'lar shohligi, ba'zan choanozoa parafiletik filumida guruhlangan eukaryotik mikroorganizmlar bilan birga (ilgari protist "shohlik"ga kiritilgan) . Ham genetik, ham ultrastrukturaviy tadqiqotlar opisthokontslarning monofiletik guruhni tashkil etishini qat'iy tasdiqlaydi.

Opisthokontslarning umumiy xususiyatlaridan biri shundaki, ko'pchilik hayvonlarning spermatozoidlari va xitrid sporalari kabi flagellat hujayralar bitta orqa flagellum bilan harakatlanadi. Bu guruh nomini beradi. Bundan farqli o'laroq, boshqa eukaryotlar guruhlaridagi flagellat hujayralari bir yoki bir nechta oldingi flagella bilan harakatlanadi. Aksariyat zamburug'lar flagellali hujayralarni hosil qilmaydi, ammo ibtidoiy qo'ziqorin xitridlari hosil qiladi, bu hozirgi qo'ziqorin turlarining umumiy ajdodida flagellum borligini ko'rsatadi.

Hayvonlar va qo'ziqorinlar o'rtasidagi yaqin aloqani 1987 yilda Kavalier-Smit taklif qilgan, u norasmiy opisthokonta nomini ishlatgan (rasmiy nom xitridlar uchun ishlatilgan). Kashfiyot keyingi genetik tadqiqotlar bilan tasdiqlangan. Dastlabki filogeniyalar opisthokontslarni o'simliklar va mitoxondriyalarga ega bo'lgan boshqa guruhlarga yaqin joyda joylashtirdi, ammo bu belgi har xil. Kavalier-Smit va Stexmanning ta'kidlashicha, birlashgan eukaryotlar, masalan, opikokonts va amoebozoa, unikonts deb ataladi, ular bikonts deb nomlangan boshqa ikkitali eukaryotlardan ajralib chiqqan.

Opisthokonts holomikota yoki nukletmitsaga (qo'ziqorinlar va qo'ziqorinlarga hayvonlardan ko'ra ko'proq yaqinroq bo'lgan barcha organizmlar) va xolozoaga (hayvonlar va qo'ziqorinlarga qaraganda hayvonlar bilan yaqinroq bo'lgan barcha organizmlar) bo'linadi; Holomikota/Xolozoa bo'linishiga asoslangan bazal opistokontslar hali aniqlanmagan.

Asosiy nuqtalar

  • Opisthokontslarni birlashtiruvchi xususiyati - flagellumning, ba'zan faqat ajdodlar yoki hayot aylanishining ma'lum bir nuqtasida bo'lishi.
  • Genetik ketma-ketlik opisthokontslarning genetik jihatdan bog'liqligini tasdiqladi.
  • Opisthokonts ikki guruhga bo'linadi: holomikota (qo'ziqorinlarni o'z ichiga oladi) va holozoa (hayvonlarni o'z ichiga oladi).

Asosiy shartlar

  • monofilOrganizmlarning bitta filumiga (yoki boshqa taksoniga) tegishli yoki unga ta'sir qilish.
  • flagellum: Protistlarda, qamish yoki ovqatlantirish uchun ishlatiladigan, qamchiga o'xshash uzun membrana bilan o'ralgan organel.

Amorfiya

Amorfiya [1] - bu bazal Amoebozoa va Obazoa o'z ichiga olgan taksonomik super guruh a'zolari. Ikkinchisida qo'ziqorinlar, hayvonlar va choanomonada yoki choanoflagellatlar mavjud bo'lgan Opisthokonta mavjud. Ushbu guruh a'zolarining taksonomik yaqinliklari dastlab 2002 yilda Tomas Kavalier-Smit tomonidan tasvirlangan va taklif qilingan. [2] [4]

Xalqaro protistologlar jamiyati, protozoyalar taksonomiyasi bo'yicha tan olingan organ, 2012 yilda Unikont atamasini amorfaga o'zgartirishni tavsiya qilgan, chunki "Unikont" nomi keyinchalik ISP mualliflari va boshqa olimlar rad etgan faraz qilingan sinapomorfiyaga asoslangan. [1] [5]


Tarix

Hayvonlar va zamburug'lar o'rtasidagi yaqin aloqani 1987 yilda Tomas Kavalier-Smit taklif qilgan [3], u norasmiy opisthokonta nomini ishlatgan (rasmiy nomi 1956 yilda Copeland tomonidan chitridlar uchun ishlatilgan) va keyinchalik genetik tadqiqotlar tomonidan qo'llab-quvvatlandi. [13]

Erta filogenlar zamburug'larni o'simliklar va yassi kristali mitoxondriyaga ega bo'lgan boshqa guruhlar yoniga joylashtirgan, lekin bu belgi turlicha. Yaqinda aytilganidek, xolozoa (hayvonlar) va holomikota (zamburug'lar) o'simliklardan ko'ra bir -biri bilan chambarchas bog'liq, chunki opistokontslarda karbamoil fosfat sintetaza, dihidroorotaza va aspartat karbamoyltransferaza uch marta birlashadi. o'simliklar mavjud va o'simliklar opistokontsda bo'lmagan timidilat sintaz va dihidrofolat reduktaza birikmasiga ega. Hayvonlar va zamburug'lar ham o'simliklardan ko'ra amyoba bilan, o'simliklar esa hayvonlar yoki zamburug'lardan ko'ra SAR superguruhi protistlar bilan yaqinroq bog'liq. Hayvonlar va zamburug'lar o'simliklardan farqli o'laroq geterotroflardir va zamburug'lar o'simliklar kabi turg'un bo'lsa-da, turg'un hayvonlar ham bor.

Kavalier-Smit va Stexmann [14] birlashuvchi eukaryotlar, masalan, opikokonts va amoebozoa, unikonts deb ataladi, ular bikonts deb nomlangan boshqa ikkitali eukaryotlardan ajralib chiqqanidan ko'p o'tmay ajralib chiqadi.


8.16C: Opisthokonts - Hayvonlar va zamburug'lar - Biologiya

Opisthokonta eukariotlarning katta superguruhidir, shu jumladan metazoanlar va zamburug'lar. Bundan tashqari, Opisthokonta shuningdek, ba'zi flagellate (choanoflagellates), amoeboid (masalan, Nuclearia) va sporozoan (masalan, Ichthyosporea, Microsporidia) protistlarini o'z ichiga oladi. Opisthokontlar fagotrof yoki osmotrof (saprob, parazit)dir. Ba'zi a'zolar quruqlikdagi o'simliklar yoki suv o'tlari (masalan, likenlar, mikorizal zamburug'lar, marjonlar) bilan simbiotik tarzda yashaydi.

Opisthokonta-ning eng o'ziga xos xususiyatlaridan biri bu flagellate hujayraning arxitekturasi va bu xususiyat "Opistho-konta" nomining kelib chiqishi. Flagellate xujayrasi orqa tomondan kiritilgan bitta flagellumga ega. Mitokondriyal kristallar odatda tekis. Opisthokontlar ba'zan aktin filamentlari tomonidan qo'llab-quvvatlanadigan "filipodiya" ga ega. Filopodiya qo'ziqorin va nukleariidlarda mayda va tarvaqaylab ketadi, lekin ular (ba'zan "tentacles" deb ham ataladi) filozoyada yo'q. Xoanoflagellatlar va gubkalarda (Metazoa) filopodiyalar zarrachalarni ushlash apparatini hosil qiladi, rangi flagellum atrofida. Metazoa eng ilg'or ko'p hujayrali tashkilotga ega. Hujayralararo birikma va o'zaro ta'sir uchun ba'zi oqsillar Naziriyada mavjud.

Corallochytrium (Corallochytrea) & alfa-aminoadipat (AAA) yo'lida ishtirok etadigan & alfa-aminoadipat reduktaza (& alfa-AAR) ga ega bo'lganligi sababli, bu organizm ba'zida hayvonlarga qaraganda qo'ziqorinlar bilan chambarchas bog'liq deb hisoblanadi (Sumathi va boshq. 2006. Protist 157: 363-376). Protistan opisthokonts ba'zan Choanozoa yoki Mesomycetozoa tasniflanadi. Biroq, bu taksilar bu ma'noda monofil emas. Mikrosporidiyalar va miksozoanlar an'anaviy ravishda protozoalarga (sporozoalarga) tasniflangan. Biroq, so'nggi tadqiqotlar shuni ko'rsatadiki, ular mos ravishda soddalashtirilgan qo'ziqorinlar va hayvonlardir.


Opisthokont

Ushbu blog uchun men tanlagan ism ko'pchilik uchun notanish atama bo'lishi mumkin. Bu, ehtimol, notanish tushunchani ham ifodalaydi, shuning uchun men muloyimlik bilan boshlayman. Bu o'ziga xos, katta va (odamlar uchun) juda muhim organizmlar guruhini bildiruvchi atama. Guruhning ahamiyati, ehtimol, inson ekanligini tushungandan keyin tushunarli bo'ladi bor opisthokonts. Shunday bo'lsa-da, barcha boshqa hayvonlar. Hamma qo'ziqorinlar ham shunday! Guruhni yaxlitlash hayvonlar yoki zamburug'lar yoki ikkalasi bilan bog'liq bo'lgan bir qator bir hujayrali organizmlardir. Bu guruhda o'simliklar, suv o'tlari va boshqa ko'plab organizmlar, shu jumladan barcha bakteriyalar yo'q.

Hayvonlar va zamburug'lar o'simliklarda bo'lmagan umumiy nimaga ega? Xo'sh, sperma hujayrasini o'ylab ko'ring. Bu yirtqichlarga o'xshash narsa, taxminan sharsimon hujayra tanasi va orqasida dumga o'xshash bitta flagellum. Hujayra dumini qimirlatib, xuddi xuddi tayoqchaga o'xshab, o'z bayroqchasini qimirlatib suzadi. Bu sodir bo'lganda, bu juda g'ayrioddiy hujayra turi. Ko'pchilik boshqa bayroqchali organizmlar o'zlarining flagellalari bilan suzadilar va o'zlarini atrofdagi muhitdan o'tkazadilar. Faqat hayvonlarda, qo'ziqorinlarda va tegishli mikroblarda topilgan bayroqchali hujayralar o'z bayroqchalari ortida suzadilar. Bu nomni keltirib chiqaradi: "opistho-" "orqada" degan ma'noni anglatadi va "-kont" flagellumni anglatadi.

Kundalik tajribani hisobga olgan holda, bu kichik farqni topish uchun osongina kechirilishi mumkin. Ko'pchiligimiz uchun hayvonlar - bu atrofda harakatlanadigan va ovqatlanadigan narsalar, o'simliklar va zamburug'lar esa tuproqda joylashgan. Biroq, erga ildiz otgan hayvonlar ham bor (gubkalar, marjonlar va dengiz chig'anoqlari) va yemaydigan hayvonlar (masalan, dengizning chuqur gidrotermal teshiklari yaqinida yashovchi qurtlar). Tuproqda o'smaydigan qo'ziqorinlar bor (xamirturushlar, masalan, zamburug'lar va hech narsaga ildiz otmaydi). Ko'rinib turibdiki, kundalik tajriba, hayotdan ilgarilab ketgan narsalarni tasniflash uchun etarli emas.

Ilm -fan, hozirgi holatiga etib borish uchun vaqt ajratdi. Bir necha o'n yillar oldin zamburug'lar "pastki o'simliklar" qatoriga kiritilgan, chunki ularning hujayralari qattiq hujayra devorlari bilan o'ralgan, bu xususiyat o'sha paytda "o'simlik" ni belgilaydi. Biroq, o'sha vaqtdan beri hujayra devorlarini tashkil etuvchi materiallar mutlaqo bir-biriga bog'liq emasligi ko'rsatildi (ular o'simliklardagi shakarlardan va zamburug'lardagi oqsillardan olingan). Eng muhimi, shubhasiz, har biri bilan chambarchas bog'liq bo'lgan, taniqli hamkasblarining bir hujayrali versiyalariga o'xshash, hujayralar devorining izlari yo'q. Boshqacha qilib aytganda, o'simliklar va zamburug'larning umumiy ajdodi hujayra devoriga ega emas edi, bu belgi gomoplaziya bo'lib, hayot tarixida bir necha marta rivojlangan narsadir.

Buni genetik tahlil tasdiqlaydi. Evolyutsiya tarixining aksariyat gipotezalari (baribir mavjud bo'lgan organizmlar) kompyuterlar turli organizmlarning taqqoslanadigan genlarining DNKsini tahlil qilish orqali amalga oshiriladi va ular hayvonlarni zamburug'lar bilan bog'laydi, o'simliklarni istisno qiladi. (Istisnolar mavjud -- har doim istisnolar mavjud -- lekin ular ko'p evolyutsion "shovqin"ga ega bo'lgan genlardan kelib chiqadi. Boshqacha qilib aytganda, bunday genlar yo etarlicha katta emas yoki hayvonni hal qilish uchun etarli ma'lumotni saqlash uchun juda tez rivojlanadi. O'simliklar/qo'ziqorinlarning har qanday ishonchliligi bilan bog'liqligi. Bu kompyuter tahlillarining ishonchliligini ko'rsatadigan statistik testlar mavjud va ular maqbul deb topilganlar deyarli har doim hayvonlar va zamburug'lar o'rtasidagi yaqin aloqani qo'llab -quvvatlaydi.)

Genlarni tahlil qilish ularni evolyutsiya tarixini to'g'ridan -to'g'ri qayta qurish uchun ishlatishdan tashqari. Masalan, hayvonlarda, zamburug'larda va ularning yaqin qarindoshlarida bo'lgan ellikka yaqin nukleotiddan (DNK "alifbosi"ning "harflari") qo'shimcha cho'zilgan DNK replikatsiyasida ishlatiladigan genlardan biriga qo'shilish mavjud. , va boshqa hech narsa. Bu unchalik muhim emasdek tuyulishi mumkin, lekin koʻrib chiqilayotgan gen shunchalik muhimki, u osonlikcha oʻzgarmasdir (ilmiy tilda aytganda, u “evolyutsion tarzda saqlanib qolgan”) va, ehtimol, bundan ham muhimi, kiritishning oʻzi saqlanib qolgan. Boshqacha qilib aytganda, bir xil nukleotidlar (yoki ulardan aniq hosilasi) hamma opisthokontslarda bir joyda bo'ladi.

Genetik bo'lmagan ma'lumotlar ikkala guruhni bog'lashga yordam beradi. Hayvonlar va zamburug'larning bir hujayrali qarindoshlaridagi alohida hujayralar arxitekturasi tashqi va ichki tomondan juda o'xshash. Bu elektron mikroskop paydo bo'lgunga qadar ko'rinmas edi, bu ikki guruhni bog'laydigan ko'plab xususiyatlar yorug'lik mikroskopida ("oddiy" turdagi) ko'rish uchun juda kichikdir yoki boshqa, yanada ajoyib xususiyatlar foydasiga osonlikcha e'tibordan chetda qolar edi. ularning ko'pchiligi (yuqorida aytib o'tilgan hujayra devorlari singari) boshqa usullar yordamida tekshirilganda uzilmaydigan aloqalarni nazarda tutishi mumkin.

Bu xususiyatlarga sitoskeletning tarkibiy qismlari, hujayraga shakl beradigan oqsillarga asoslangan tayoqlar va naychalar to'plami kiradi. Flagellaning joylashishi va replikatsiyasi ham saqlanib qolgan xususiyat deb hisoblanadi. Bitiruv malakaviy ishimning asosiy qismi mana shu narsalarni o'rganishga bag'ishlangan, biroq opistokokontslarning guruh sifatida uyg'unligi bugungi kunda deyarli so'roq qilinmaydi, uning o'ziga xos xususiyatlarining o'ziga xosligi noma'lum. Elektron mikroskopi juda ko'p ma'lumot to'planishi uchun etarli darajada uzoq vaqt o'tmagan va kuzatilganlarning aksariyati bir nechta taniqli organizmlarga qaratilgan. Bizga tirik mavjudotlarning o'zaro munosabatlari haqida ko'proq ma'lumot bera oladigan organizmlar ko'pincha noaniq va yomon o'rganilmagan bo'lib, bu holat, ehtimol, bu holatdan ko'ra kuchliroqdir.

Ammo bitta xususiyat borki, u tezda kuzatiladi va izchil bo'ladi, bu flagella soni va joylashuvi. Men aytganimdek, ko'pchilik organizmlarning hujayralarining old uchida flagella bor va ular bilan o'zlarini tortib oladilar, opistokokonlar hujayralarini atrofidan itarish odatiy holdir. Bundan tashqari, ko'pchilik opistokokont bo'lmagan hujayralarda ikkitadan paydo bo'ladigan yoki aniqki, ikkitadan bayroqchaga ega bo'lgan ajdodlardan kelib chiqqan, opisthokontsning barcha flagellani ular bilan bog'lanmagan holda paydo bo'ladi. Bu juda muhim narsa emasdek tuyulishi mumkin, lekin shuni yodda tutish kerakki, hayvonlar va o'simliklar va zamburug'larning tafovutini muhokama qilishda biz bir hujayrali organizmlar evolyutsiyasini muhokama qilamiz. Shu nuqtai nazardan, flagellalarning joylashuvi va soni kabi ahamiyatsiz ko'rinadigan narsalar juda muhim bo'lishi mumkin.

Shunday qilib, biror narsani opisthokont sifatida tasniflash ko'pchilik uchun tabiiy narsa emas. Bu noaniq va ahamiyatsiz farq kabi ko'rinishi mumkin. Hayvonlar va zamburug'larni bir-birining eng yaqin ko'p hujayrali qarindoshlari sifatida tasniflash (hozircha) tibbiyot yoki qishloq xo'jaligi yoki ko'pchilik sezadigan boshqa hech qanday oqibatlarga olib kelmaydi. Ammo opisthokont gipotezasi, biz bilganimizdek, tirik mavjudotlar munosabatlarining aniq ta'rifidir: bu biz tegishli faktlarni eng yaxshi tushunishimiz va fan haqiqatga yaqinlashishi mumkin.


Opisthokonta nima?

Opisthokonts guruhining flagellatli hujayralarida ko'rinadigan bitta orqa flagellum uchun nomlangan. Boshqa protistlarning flagella old qismi va ularning harakati hujayralarni oldinga siljitadi, opisthokonts esa itariladi. Opisthokonts protist a'zolari gubkalar va, ehtimol, barcha hayvonlarning umumiy ajdodiga o'xshaydi, deb hisoblanadigan hayvonlarga o'xshash choanoflagellatlarni o'z ichiga oladi. Choanoflagellatlar bir hujayrali va kolonial shakllarni o'z ichiga oladi va ularning 244 ga yaqin ta'riflangan turlari mavjud. Bu organizmlarda bitta, apikal flagellum mikrovilluslardan tashkil topgan qisqaruvchi yoqa bilan o'ralgan. Yoqa protist tomonidan yutish uchun bakteriyalarni filtrlash va yig'ish uchun ishlatiladi. Xuddi shunday oziqlantirish mexanizmi gubkalarning yoqa hujayralarida ham uchraydi, bu esa choanoflagellatlar va hayvonlar o'rtasidagi bog'liqlikni ko'rsatadi.

Mezomitsetozoa parazitlarning kichik guruhini, birinchi navbatda, baliqlarni va odamlarni parazit qila oladigan kamida bitta shaklni hosil qiladi. Ularning hayotiy tsikllari yaxshi tushunilmagan. Bu organizmlar alohida qiziqish uyg'otadi, chunki ular hayvonlar bilan chambarchas bog'liqdir. Ilgari, ular morfologiyasiga ko'ra qo'ziqorinlar va boshqa protistlar bilan guruhlangan.


Biologiya II 28 -bob

Prokariotlarning hujayralaridan farqli o'laroq, eukaryotik hujayralar yadro va boshqa membrana bilan chegaralangan organellalarga ega, masalan, mitoxondriya va Golji apparati.

Bu protistlarning ko'pchiligi bir hujayrali bo'lishiga qaramay. Bir hujayrali protistlar haqli ravishda eng oddiy eukaryotlar hisoblanadi, lekin hujayra darajasida ko'p protistlar juda murakkab.

Bir hujayrali protistlar bir xil muhim funktsiyalarni bajaradilar, lekin ular buni ko'p hujayrali organlar emas, balki subhujayra organellalari yordamida bajaradilar.

Fotosintezga ham, geterotrofiyaga ham qodir organizm.

Ba'zi protistlar bu xususiyatni namoyish etadilar.

Xloraraxniofitlar, ehtimol, o'z plastidalari bilan fotosintezni amalga oshiradigan va o'ziga xos mayda vestigial yadroni o'z ichiga olgan yashil algni heterotrofik eukaryot yutib yuborishi natijasida paydo bo'lgan.

Xloraraxinofitlar boshqa eukaryotni o'z ichiga olgan eukaryotdan paydo bo'lgan degan gipotezaga muvofiq, ularning plastidlari to'rtta membrana bilan o'ralgan. Ikki ichki membrana qadimgi siyanobakteriyalarning ichki va tashqi membranalari sifatida paydo bo'lgan. Uchinchi membrana yutgan suv o'tlarining plazma membranasidan, eng tashqi membranasi esa geterotif eukariotning oziq-ovqat vakuolasidan hosil bo'ladi. Boshqa protistlarda ikkilamchi endosimbiyoz natijasida olingan plastidlar uchta membrana bilan o'ralgan bo'lib, evolyutsiya jarayonida dastlabki to'rt membranadan biri yo'qolganligini ko'rsatadi.

Oddiy mitoxondriyalarga ega bo'lmagan va membranalar bilan chegaralangan organellalari boshqa protistlarga qaraganda kamroq bo'lgan guruh.

"Amitokondriy protistlar" ning ko'pchiligida mitoxondriya bor, lekin ular kamayadi.

Eukaryotik daraxtning ildizi noma'lum bo'lganligi sababli, barcha beshta supergruppa bir vaqtning o'zida umumiy ajdodlardan ajralib chiqadi - bu noto'g'ri, lekin birinchi navbatda qaysi organizmlar boshqalardan ajralib chiqqanligi noma'lum.

  • Qizil, yashil, ikkilamchi endosimbioz

Zamburug'lar va hayvonlar Unikonta super guruhiga kiradi.

kabi parazitlar qazib olinadi Giardia, shuningdek ko'plab yirtqich va fotosintetik turlar.

  • Ushbu superguruhning ba'zi a'zolari hujayra tanasining bir tomonida qazilgan chuqurchaga ega. Ikkita asosiy parda (parabasalidlar va diplomatadlar) mitoxondriyalarini o'zgartirgan, boshqalari (euglenozoanlar) tuzilishi jihatidan boshqa organizmlarnikidan farq qiladi.

CChromalveolatlar Yer yuzidagi eng muhim fotosintetik organizmlarni o'z ichiga oladi. Bu guruhga suv osti kelp "o'rmonlarini" hosil qiluvchi jigarrang suv o'tlari, shuningdek, muhim patogenlar kiradi Plazmodiy, bezgakka olib keladigan va Fitoftora, bu 19-asr Irlandiyada halokatli kartoshka ochligiga sabab bo'ldi.

  • Bu guruh qadimiy ikkilamchi endosimbioz hodisasidan kelib chiqqan bo'lishi mumkin.

Bu guruh amyobalarning turlaridan iborat bo'lib, ularning ko'pchiligi shakli ipga o'xshash psevdopodiyaga ega.

  • Psevdopodiya - bu yirtqichlarni ushlashda harakatlanuvchi va hujayraning istalgan qismidan chiqib ketadigan kengaytmalar.

Eukaryotlarning bu guruhiga quruq o'simliklar bilan birga qizil suv o'tlari va yashil suv o'tlari kiradi. Qizil suv o'tlari va yashil yosunlarga bir hujayrali turlar, koloniya turlari (masalan, yashil suv o'tlari) kiradi Volvox) va ko'p hujayrali turlar. Norasmiy ravishda "dengiz o'tlari" deb nomlanuvchi yirik suv o'tlarining ko'pchiligi ko'p hujayrali qizil yoki yashil suvo'tlardir. Archaeplastida protistlari ba'zi suv jamoalarida oziq-ovqat tarmog'ining asosini tashkil etuvchi asosiy fotosintetik turlarni o'z ichiga oladi.

Yashil va qizil yosunlar Archaeplastida supergruppasiga kiradi.

Oltin va jigarrang yosunlar "Chromalveolata" supergruppasiga kiradi.

Bu eukariotlar guruhiga lob yoki naychasimon psevdopodiyaga ega amyobalar, shuningdek, hayvonlar yoki zamburug'lar bilan chambarchas bog'liq bo'lgan hayvonlar, zamburug'lar va protistlar kiradi.

Hozirgi gipotezaga ko'ra, bu unikontslar boshqa eukaryotlardan ajralib chiqqan birinchi eukaryot guruhlari bo'lishi mumkin, ammo gipoteza hali keng qabul qilinmagan.

(T/F) Excavata superguruhining aksariyat diplomonadalari va parabazalidlari anaerob muhitda uchraydi.

(T/F) Bu ikki guruhda ham plastidlar yoʻq va oʻzgartirilgan mitoxondriyalar mavjud (yaqingacha ularda mitoxondriyalar umuman yoʻq deb hisoblangan).
Haqiqiy yolg'on

Diplomatadalarda elektron funktsional transport zanjirlari yo'q, shuning uchun uglevodlar va boshqa organik molekulalardan energiya olish uchun kisloroddan foydalana olmaydi. Buning o'rniga, diplomantlar zarur energiyani anaerob biokimyoviy yo'llardan olishlari kerak.

Parabasalidlar anaerob tarzda energiya ishlab chiqaradi va yon mahsulot sifatida vodorod gazini chiqaradi.

Protetistlar kinetoplast deb nomlangan DNKning uyushgan massasini o'z ichiga olgan bitta, katta mitoxondriyaga ega.

Ular Excavata va evglenozoanlar guruhining yuqori guruhiga kiradi. Bu organizmlar flagella ichida noma'lum funktsiyali spiral yoki kristall tayoqchaga ega.

Bu protistlar tarkibiga chuchuk suv, dengiz va moiz er usti ekotizimlarida prokaryotlar bilan oziqlanadigan, shuningdek hayvonlar, o'simliklar va boshqa protistlarni parazit qiladigan turlar kiradi. Kabi Trypanosoma bu odamlarda uyqu kasalligini keltirib chiqaradi.

Hujayraning bir uchida cho'ntagi bo'lgan protistlar, ulardan bitta yoki ikkita bayroqcha chiqadi. Euglenidning ko'p turlari Evglena miksotroflar: quyosh nurida ular avtotrof, ammo quyosh nuri bo'lmaganda ular geterotrof bo'lib, atrof-muhitdan organik ozuqa moddalarini so'rib olishlari mumkin.

Boshqa ko'plab evglenidlar o'ljani yutadi fagotsitoz.

Ularning mitoxondriyalari elektron tashish zanjiriga ega emas va shuning uchun aerob nafas olishda ishlay olmaydi.

Juda katta va xilma -xil o'ta xilma -xil protistlar guruhi va yaqinda ikkita dalil asosida taklif qilingan.

1) Ba'zi (hammasi bo'lmasa ham) DNK ketma-ketligi ma'lumotlari xromaveolatlar monofiletik guruhni tashkil qilishini ko'rsatadi.

2) Ba'zi ma'lumotlar, xromalveolatlar milliarddan ko'proq yil oldin, guruhning umumiy ajdodlari, hujayrali, fotosintezli qizil yosunlarni yutib yuborgan, degan farazni tasdiqlaydi. Qizil ala birlamchi endosimbiozdan kelib chiqqan deb taxmin qilinganligi sababli, xromalveolatlarning bunday kelib chiqishi ikkilamchi endosimbiozga aylanadi.

Xromalveolatlar superguruhidagi protistlar guruhi (boshqa guruh - stramenopillar), ularning monofiliyasi molekulyar sistematika bilan yaxshi qo'llab-quvvatlanadi (kladka hosil qiladi). Strukturaviy ravishda, bu guruh turlarining plazma membranasi ostida membrana bilan bog'langan qoplari (alveolalari) bor. Alveolalarning vazifasi noma'lum, lekin ular hujayra sirtini turg'unlashtirishga yoki hujayraning suv va ion tarkibini tartibga solishga yordam berishi mumkinligi taxmin qilingan.

Alveolatlar uchta kichik guruhni o'z ichiga oladi: bir guruh flagellatlar (dinoflagellatlar), bir guruh parazitlar (apikompleksanlar) va siliyalar (kiprikchalar) yordamida harakatlanadigan protistlar guruhi.

Xromalveolatlar superguruhi va alveolatlar guruhidagi protistlar.

Bu tsellyuloza plitalari bilan mustahkamlangan hujayralar bilan tavsiflanadi. Ushbu "zirh" dagi perpendikulyar yivlarda joylashgan ikkita flagella suvda harakatlanayotganda dinoflagellatlarni sprin qiladi. Dinoflagellatlar - dengiz va chuchuk suv planktonlarining ko'p qismlari, suv yuzasiga yaqin yashaydigan mikroorganizmlar jamoalari.

  • Bu dinoflagellatlar eng muhim fotosintez turlarini o'z ichiga oladi. Biroq, ko'plab fotosintetik dinoflagellatlar miksotrofikdir va dinoflagellatlarning taxminan yarmi sof hterotrofikdir.
  • Dinoflagellatning gullab-yashnashi - aholining portlovchi o'sishi epizodlari - ba'zida qirg'oq suvlarida "qizil to'lqin" deb ataladigan hodisani keltirib chiqaradi.

Dinoflagellatning gullashi qizil alglarning ikkilamchi endosimbiozidan kelib chiqqan bo'lishi mumkin. Qizil yosun birlamchi endosimbiozdan kelib chiqqan deb ishoniladi.

Dinoflagellatning gullashi - populyatsiyaning portlashi epizodlari bo'lib, ular jigarrang qizil yoki pushti rangga aylanadi, chunki dinoflagellat plastidlarida eng ko'p uchraydigan pigmentlar - karotenoidlar bor.

Ba'zi dinoflagellatlar ishlab chiqaradigan toksinlar umurtqasiz hayvonlar va baliqlarni o'ldirishga olib keldi. Toksinlarni to'plagan mollyuskalarni iste'mol qiladigan odamlar ham, ba'zan o'limga olib keladi.

Xromalveolatlar superguruhi va alveolatlar guruhidagi protistlar.

Deyarli barcha apikompleksanlar hayvonlarning parazitlari bo'lib, ba'zilari odamning jiddiy kasalliklarini keltirib chiqaradi. Parazitlar uy egasi orqali mayda yuqumli hujayralar sifatida tarqaladi sporozoitlar.

Apikomplekslar shunday nomlanadi, chunki bir uchi ( cho'qqi) sporozoit hujayrasida xost hujayralari va to'qimalariga kirib borishga ixtisoslashgan organellalar majmuasi mavjud.

Apikompleksanlar fotosintetik bo'lmasa -da, so'nggi ma'lumotlar shuni ko'rsatdiki, ular qizil algli kelib chiqishi o'zgartirilgan plastidni (apikoplast) saqlab qoladi.

Aksariyat apikompleksanlar murakkab hayot davrlariga ega ikkalasi ham jinsiy va aseksual bosqichlar.

"Xromalveolatlar" supergruppasi va alveolatlar guruhidagi protistlar.

Ciliates - siliya yordamida harakatlanish va ovqatlantirish uchun nomlangan katta, xilma -xil protistlar guruhi. Kirpiklar hujayra yuzasini to'liq qoplashi yoki bir necha qator yoki shamlardan to'planishi mumkin. Ba'zi turlarda, bir -biriga mahkam o'ralgan siliya qatorlari birgalikda harakatlanish funktsiyasini bajaradi. Boshqa kirpiklar bir-biriga bog'langan ko'plab siliyadan yasalgan oyoqqa o'xshash tuzilmalarda yugurishadi.

Ciliatesning o'ziga xos xususiyati ikki turdagi yadrolarning mavjudligi: mayda mikronukleuslar va katta makronuklelardir. Hujayra har bir turdagi bir yoki bir nechta yadroga ega.

Genetika o'zgaruvchanligi konjugatsiyadan kelib chiqadi, bu jinsiy jarayon bo'lib, unda ikkita indivudal haploid mikronuklelarni almashadi. Kipriklar odatda ikkilik boʻlinish yoʻli bilan jinssiz yoʻl bilan koʻpayadi, bunda mavjud makronukle parchalanadi va hujayra mikroyadrolaridan yangisi hosil boʻladi. Har bir makronukleus odatda kiliat genomining bir nechta nusxasini o'z ichiga oladi.

Makronukleus genlari hujayraning oziqlanish, chiqindilarni olib tashlash va suv muvozanatini saqlash kabi kundalik vazifalarini boshqaradi.

Genetika o'zgaruvchanligi konjugatsiyadan kelib chiqadi, bu jinsiy jarayon bo'lib, unda ikkita indivudal haploid mikronuklelarni almashadi. Kipriklar odatda ikkilik boʻlinish yoʻli bilan jinssiz yoʻl bilan koʻpayadi, bunda mavjud makronukle parchalanadi va hujayra mikroyadrolaridan yangisi hosil boʻladi. Har bir makronukleus odatda kiliat genomining bir nechta nusxasini o'z ichiga oladi.

"Chromalveolatlar" supergruppasida bir guruh protistlar (boshqa guruh - alveolatlar). Stramenopillar - bu dengiz yosunlari guruhi, ular planentdagi eng muhim fotosintetik organizmlarni, shuningdek heterotroflarni o'z ichiga oladi.

Ularning ismi (stramen - somon Pilos - sochlar) ko'p sonli nozik, sochli proektsiyalarga ega bo'lgan xarakterli flagellumga tegishli. Ko'pgina stramenopillarda bu "tukli" flagellum qisqa "silliq" (tuksiz) flagellum bilan bog'langan.

Guruh diatomlar, oltin suvo'tlar, jigarrang suvo'tlar va oomisetlardan iborat.

"Xromalveolatlar" va "stramenopiles" guruhining protistlari.

  • Diatomlar bir hujayrali suvo'tlar bo'lib, ular organik matritsaga o'rnatilgan gidratlangan kremniy (kremniy dioksid) dan yasalgan noyob shishasimon devorga ega. Devor poyabzal qutisi va uning qopqog'i kabi bir-biriga yopishgan ikki qismdan iborat. Devorlari yirtqichlarning ezilgan jag'laridan samarali himoya qiladi.
  • Diatomning ko'p kuchi, agar devorlari silliq bo'lsa, ularni maydalash uchun 60% kamroq kuch kerak bo'lar edi.

Diatomlar mitoz yo'li bilan jinssiz ko'payadi, har bir qiz hujayra ota-ona hujayra devorining yarmini oladi va uning ichiga sig'adigan yangi yarmini hosil qiladi. Ba'zi turlar chidamli bosqichlar sifatida kistalarni hosil qiladi. Jinsiy ko'payish sodir bo'ladi, lekin diatomalarda keng tarqalgan emas.

Birinchi gap to'g'ri, lekin ikkinchi jumla noto'g'ri. Diatom gullari global isishni kamaytirishda foydalidir, chunki ularning tanasi fotosintez paytida havodagi karbonat angidriddan uglerodni o'z tanasiga kiritadi. Jasadlar okean tubiga cho'kadi va bakteriyalar va boshqa parchalanuvchilar tomonidan yeyiladiganlarga qaraganda kamroq parchalanadi.

"Xromalveolatlar" va "stramenopiles" guruhining protistlari.

Oltin suv o'tlari odatda ikki qavatli bo'lib, ikkala flagella ham hujayraning bir uchiga yaqin joylashgan. Xarakterli rang sariq va jigarrang karotenoidlardan kelib chiqadi.

Ko'plab oltin yosunlar chuchuk suv va dengiz planktonining tarkibiy qismlari hisoblanadi. Barcha oltin suvo'tlar fotosintetik bo'lsa-da, ba'zi turlari miksotrofikdir. Bu miksotroflar erigan organik birikmalarni o'zlashtirishi yoki oziq -ovqat zarralarini, shu jumladan tirik hujayralarni (eukaryotlar va prokaryotlar) fagotsitoz orqali yutishi mumkin.

Aksariyat turlar bir hujayrali, ammo ba'zilari mustamlakadir.

"Xromalveolatlar" va "stramenopiles" guruhining protistlari.

Jigarrang yosunlar eng murakkab va eng katta suv o'tlari hisoblanadi. Hammasi ko'p hujayrali va ko'pchiligi dengiz.

Jigarrang yosunlarga o'simliklarga o'xshash maxsus to'qimalar va organlarga ega bo'lgan turlar kiradi. Ammo morfologik va DNK dalillari shuni ko'rsatadiki, o'xshashliklar yosunlar va o'simliklarning avlodlarida mustaqil ravishda rivojlangan va shuning uchun o'xshash emas, balki gomologik.

O'simliklarga o'xshash jigarrang yosunlar deyiladi talus ( talli, talli - unib chiqadi). Oddiy talus o'simlik tanasidan farqli o'laroq, yosunlarni mahkamlab turadigan ildizsimon tayoqchadan va bargsimon pichoqlarni ushlab turuvchi poyaga o'xshash bo'lakdan iborat.

Jigarrang yosunlar avlodlar almashinuvi bilan ko'payadi - ko'p hujayrali haploid va diploid shakllarining o'zgarishi.

Jigarrang yosunlar Chromalveolata yuqori guruhiga, quruqlikdagi o'simliklar esa Archaeplastida supergruppasiga tegishli.

Jigarrang yosunlarga o'simliklarga o'xshash maxsus to'qimalar va organlarga ega bo'lgan turlar kiradi. Ammo morfologik va DNK dalillari shuni ko'rsatadiki, o'xshashliklar yosunlar va o'simliklarning avlodlarida mustaqil ravishda rivojlangan va shuning uchun o'xshash emas, balki gomologik.

Diploid shaxslar sporofit deb ataladi, chunki u spora hosil qiladi. Sporalar gaploid bo'lib, flagella yordamida harakatlanadi zoosporlar. Zoosporalar jinsiy hujayralar hosil qiluvchi gaploid erkak va urgʻochi gametofitlarga aylanadi. Ikki gametaning birlashishi (urug'lanish yoki singamiya) natijasida diploid zigota hosil bo'ladi, u pishib, yangi sporofitni keltirib chiqaradi.

Ikki avlodda, heteromorfiklar uchun sporofitlar va gametofitlar tuzilish jihatidan farq qiladi.

Izmorf avlodlar uchun sporofitlar va gametofitlar bir-biriga o'xshash, ammo ular xromosoma sonida farq qiladi.

Xromalveolatlar superguruhi va stramenopillar guruhidagi protistlar.

Oomitsetlarga suv qoliplari, oq zanglar va chiriyotgan chiriyotgan kiradi. Morfologiyaga ko'ra, ular ilgari zamburug'lar sifatida tasniflangan, ammo ular zamburug'lar bilan bog'liq emas va ehtimol konvergent evolyutsiya bilan bog'liq. Oomitsetlarda ham, zamburug'larda ham filamentsimon tuzilmalarning sirt-hajm nisbati yuqori bo'lishi oziq moddalarni atrof-muhitdan o'zlashtirishni kuchaytiradi.

Farqlardan biri shundaki, oomitsetlarda odatda tsellyulozadan yasalgan hujayra devorlari bo'ladi, qo'ziqorinlarning devorlari asosan boshqa polisaxarid xitindan iborat.

Oomitsetlar plastid uradigan ajdodlardan kelib chiqqan bo'lsada, ular endi plastidlarga ega emaslar va fotosintez o'tkazmaydilar. Buning o'rniga ular odatda parchalovchi yoki parazit sifatida ozuqa moddalarini oladi.

Ko'pchilik suv mog'orlari parchalanuvchidir. Oq zanglar va chiriyotganlar odatda quruqlikda o'simlik parazitlari sifatida yashaydilar.

Yosunlar va avlodlar almashinadigan o'simliklar ko'p hujayrali haploid bosqichga ega va ko'p hujayrali diploid bosqich.

Qolgan ikkita hayot tsiklida ham haploid bosqich, ham diploid bosqich bir hujayrali bo'ladi.

Rizariya supergruppasi xloraraxniofitlar, foraminiferanlar va radiolarianlar guruhlarini o'z ichiga oladi.

Rizariyadagi ko'plab turlar amyoba deb ataladigan organizmlar qatoriga kiradi. Ilgari amyobalar psevdopodiyalar, hujayra yuzasining deyarli har qanday joyidan bo'rtib chiqishi mumkin bo'lgan kengaytmalar yordamida harakatlanadigan va zaiflashadigan protistlar sifatida aniqlangan.

Amoeba psudopodiumni cho'zish va uchini mahkamlash orqali harakatlanadi. Amyobalar nafaqat Rhizaria superguruhi ichida joylashgan va ko'plab uzoqda joylashgan eukaryotik taksonlar bo'ylab tarqalgan. Rhizaria turkumiga mansub ko'pchilik morfologik jihatdan boshqa amyobalardan ipsimon psevdopodiyaga ega bo'lganligi bilan ajralib turadi.

Rizariyaliklar supergruppasidagi protistlar. Bular sifatida ham tanilgan teshiklar - g'ovakli qobiqlari uchun atalgan, testlar deb ataladi.

Forma sinovlari kaltsiy karbonat bilan qotib qolgan bir bo'lak organik materialdan iborat. Teshiklar bo'ylab cho'zilgan psevdopodiya suzish, sinov hosil qilish va oziqlantirishda ishlaydi. Ko'pgina teshiklar, shuningdek, sinovlar ichida yashovchi simbiotik suv o'tlarining fotosintezidan ozuqa oladi.

Barcha aniqlangan quduq turlarining 90% fotoalbomlardan ma'lum.

Rhizarians superguruhidagi protistlar.

Bu protistlarning nozik, murakkab nosimmetrik ichki skeletlari bor, ular odatda silikadan qilingan. Bu protistlarning psevdopodiyasi markaziy tanadan tarqaladi va mikrotubulalar to'plami bilan mustahkamlanadi. Mikronaychalar sitoplazmaning yupqa qatlami bilan qoplangan bo'lib, u psevdopodiyaga yopishib qolgan kichikroq mikroorganizmlarni o'z ichiga oladi.

Odamlar va zamburug'lar odamlar va o'simliklar yoki zamburug'lar va o'simliklardan ko'ra ko'proq bog'liqdir.

Siyanobateriumni qamrab olgan qadimgi protistdan kelib chiqqan monofil super guruh.

Guruh qizil yosunlar, yashil yosunlar va quruqlik o'simliklaridan iborat.

More than a billion years ago, a heterotrophic protist acquired a cyanobaterial endosymbiont, and the photosynthetic descendants of this ancient protist evolved into red algae and green algae. The lineage that produced green algae, gave rise to land plants.

Prostis within the supergroup Archaeplastida.

Red algae are the most abundant large algae in the warm coastal waters of tropical oceans. Their accestory pigments allow them to absorb blue and green light, which penetrate relatively far into the water.

Most red algae are multicellular, although none are as large as the giant brown kelps.

The thalli of many red algae are filamentous, often branched and interwoven in lacy patterns. The base of the thallus is usually differentiated as a simple holdfast.

Red algae have especially diverse life cycles, and alternation of generations is common. Unlike other algae, they have no flagellated stages in their life cycle and depend on the water currents to bring gametes together for fertilization.

Protists within the supergroup Archaeplastida.

Green algae have an ultrastructure and pigment composition much like the chloroplasts of land plants.

Some systematists advocate including green algae in an expanded "plant" kingdom, Viridiplantae. Phylogenetically, this change makes sense, since otherwise the green algae are a paraphyletic group.

Green algae are divided into two main groups: chlorophytes and charophyceans.

Larger size and gereater complexity evolved in chlorophytes by three different mechanisms:

1) The formation of colonies of individual cells, as seen in Volvox and in filamentous forms that contribute to the stringy masses known as pond scum.

2) The formation of true multicellular bodies by cell division and differentiation, as seen in the seaweed Ulva

3) The repeated division of nuclei with no cytoplasmic division, as seen in multinucleate filaments of Kaulerpa.

1) The formation of colonies of individual cells, as seen in Volvox and in filamentous forms that contribute to the stringy masses known as pond scum.

2) The formation of true multicellular bodies by cell division and differentiation, as seen in the seaweed Ulva

3) The repeated division of nuclei with no cytoplasmic division, as seen in multinucleate filaments of Caulerpa.

Nearly all species of chlorophytes reproduce sexually by means of biflagellated gametes that have cup-shaped chloroplasts.

Alternation of generations have evolved in life cycles of chlorophytes, including Ulva, in which the alternate generations are isomorphic.

Ulva's thallus contains many cells and is differentiated into lifelike blade and roolike holdfast. Caulerpa's thallus is composed of multinucleate filaments without cross-walls, so it is essentially one large cell.

1) The formation of colonies of individual cells, as seen in Volvox and in filamentous forms that contribute to the stringy masses known as pond scum.

2) The formation of true multicellular bodies by cell division and differentiation, as seen in the seaweed Ulva

3) The repeated division of nuclei with no cytoplasmic division, as seen in multinucleate filaments of Caulerpa.

A recently proposed, extremely diverse supergroup of eukaryotes that includes animals, fungi and some protists.

There are to major clades of unikonts, the amoebozoans va opisthokonts (animals, fungi and closely related protist groups).

The root of the eukaryote phylogenetic tree is unknown but it has been proposed that the unikonts were the first eukaryotes to diverge from eukaryotes. Stechmann and Smith proposed that the supergroup Unikonta did not have DHFR-TS gene fusion while hammasi other supergroups experienced the fusion.

A group of protists within the supergroup Unikonta and the clade amoebozoan.

Slime molds, or mycetozoans, were once thought to be fungi because they produce fruiting bodies that aid in spore dispersal. However, the resemblance between slime molds and fungi appears to be an example of evolutionary convergence.

Slime molds have diverged into two main branches, plasmodial slime molds and cellular slime molds - distinguished in part by their unique life cycles.

Plasmodial slime molds, the diploid condition is the predominant part of the life cycle, whereas cellular slime molds are haploid organisms. (only the zygote is diploid).

Both are categorized in the Unikonata supergroup under amoebozoan.

In most plasmodial slime molds, the diploid condition is the predominant part of the life cycle. At one stage of their life cycle, they form a mass called a plasmodium, which is a single mass of cytoplasm that is undivided by plasma membranes and contains many diploid nuclei.

In cellular slime molds, they are haploid organisms (only the zygote is diploid). Although the mass of cells resembles a plasmodial slime mold, the cells remain separated by their individual plasma membranes.

They also have fruiting bodies that function in asexual, rather than sexual reporduction.

Protists within the supergroup Unikonta and clade amoebozoans that are not free-lving (unlike the others), that belong to the genus Entamoeba serving as parasites. They infect all classes of vertebrates as well as some invertebrates.

Humans are host to at least six species of Entamoeba, but only one, E. histolytica is known to be pathogenic.

The clade within Unikonta that includes an extremely diverse group of eukaryotes such as animals, fungi, and several groups of protists.

Two groups to mention are choanoflagellates which are more closely related to animals than to other protists and nucleariids that are more closely related to fungi than other protists.

Excavates - include protists with modified mitochondria and protists with unique flagella.

Chromalveolates - may have originated by secondary endosymbiosis

Rhizarians - a large diverse group of protists defined by DNA similarities

Archaeplastida - Red algae and green algae are the closest relative of land plants

Unikonts - include protists that are closely related to fungi and animals.

Diplomonads and parabasalids - modified mitochondria.

Euglenozoans - spiral or crystalline rode inside flagella

Alveolates - Membrane-bounded sacs (alveoli) beneath plasma membrane

Stramenopiles - Hairy and smooth flagella

Forams - Amoebas with threadlike pseudopodia and a porous shell

Radiolarians - Amoebas with threadlike pseudopodia radiating from central body

Red algae - Phycoerythrin (accessory pigment)

Green algae - Plant-type chloroplasts

Amoebozoans - Amoebas with lobe shapped pseudopodia

Opisthokonts - Tons. (includes fungi and animals.)

Plastids that are surrounded by more than two membranes are evidence of

a) evolution from mitochondria
b) fusion of plastids
c) origin of plastids from archaea
d) secondary endosymbiosis
e) budding of the plastids from the nuclear envelope.

Biologists suspect that endosymbiosis gave rise to mitochondria before plastids partly because

A) mitochondrial DNA is less similar to prokaryotic DNA than is plastid DNA
B) the products of photosynthesis could not be metabolized without mitochondrial enzymes
C) mitochondrial proteins are synthesized on cytosolic ribosomes, whereas plastids utilize their own ribosomes.
D) without mitochondrial CO2 production, photosynthesis could not occur.
E) all eukaryotes have mitochondria (or their remnants) whereas many eukaryotes do not have plastids

Which grroup is noto'g'ri paired with its description?

A) apicomplexans - parasites with intricate life cycles
B) diatoms - important producers in aquatic communities
C) rhizarians - morphologically diverse group defined by DNA similarities
D) diplomonads - protists with modified mitochondria
E) red algae - acquired plastids by secondary endosymbiosis

Based on the phylogenetic tree in the figure below, which of the following statements is correct?

A) The most recent common ancestor is older than that of Chromalveolata
B) The most basal (first to diverge) eukaryotic supergroup cannot be determined
C) Excavata is the most basal eukaryotic supergroup.
D) The most recent ancestor of Chromalveolata is older than that of Rhizaria
E) The most recent common ancestor of red algae and land plants is older than that of nucleariids and fungi.

Which protists are in the same eukaryotic supergroup as land plants?

A) green algae
B) dinoflagellates
C) red algae
D) brown algae
E) both a and c

In life cycles with alternation of generations, multicellular haploid forms alternate with

A) multicellular diploid forms.
B) unicellular diploid forms.
C) multicellular polypoid forms.
D) multicellular haploid forms
E) unicellular haploid forms.


Qisqartmalar

Cell Division Cycle 3 - Group 2 septin from the yeast Saccharomyces cerevisiae, often used as a reference septin

C-Terminal Extension: The carboxy terminal end of a septin protein that is highly variable across septins groups

N-Terminal Extension: The amino terminal end of a septin protein that is highly variable across septin groups

Polybasic Domain: Region of a septin protein found amino-terminal to the GTP binding domain, largely composed of basic residues. Also referred to as the Phosphoinositol Binding domain due to its requirement for septins to bind phosphoinositol


Opisthokont

The name that I have chosen for this blog is bound to be an unfamiliar term for most people. It probably represents an unfamiliar concept as well, so I will start gently. It is a term that denotes a specific, large, and (to humans) very important group of organisms. The importance of the group is probably understandable once one understands that humans bor opisthokonts. So, however, are all other animals. So are all fungi! Rounding out the group are a number of single-celled organisms known to be related to either animals or fungi or both. Notably absent from this group are plants, algae, and quite a few other organisms, including all bacteria.

What can animals and fungi have in common that plants do not? Well, think of a sperm cell. This is a tadpole-like thing, with a roughly spherical cell body and a single, tail-like flagellum trailing behind. The cell swims by wiggling its flagellum, again much like a tadpole swims by wiggling its tail. As it happens, this is a very unusual cell type. Most other flagellated organisms swim with their flagella in front, pulling themselves through the surroinding medium. Only the flagellated cells found in animals, fungi, and related microbes swim with their flagella behind. This gives rise to the name: "opistho-" means "behind", and "-kont" refers to the flagellum.

One could easily be forgiven for finding this a minor difference, given everyday experience. To most of us, animals are things that move around and eat things, and plants and fungi are rooted in the ground. However, there are animals that are rooted to the ground as well (including sponges, corals, and sea squirts), and animals that do not eat (such as some of the worms living near deep sea hydrothermal vents). There are fungi that do not grow in the ground (yeasts are fungi, for instance, and do not root themselves in anything). Everyday experience, it turns out, is insufficient to categorise life science has moved well beyond that.

Science has taken its time to get to where it is today, though. Decades ago, fungi were classed amongst the "lower plants" because their cells are surrounded by rigid cell walls, a characteristic then thought to define a "plant". However, it has since been shown that the materials that make up those cell walls are completely unrelated (they are derived from sugars in plants and from proteins in fungi, for instance). More importantly, the organisms indisputably most closely related to each, which look like single-celled versions of their better-known counterparts, lack any vestige of the cell wall. In other words, the common ancestor of plants and fungi did not have a cell wall this character is a homoplasy, something that evolved more than once in the history of life.

Genetic analysis confirms this. Most hypotheses of evolutionary history (of extant organisms, anyway) are now made by having computers analyse the DNA of comparable genes from different organisms, and these tend to connect animals to fungi, to the exclusion of plants. (There are exceptions -- there are always exceptions -- but those are from genes with a lot of evolutionary "noise". In other words, such genes are either not large enough or evolve too quickly to retain enough information to resolve the animal/plant/fungus relationship with any reliability. There are statistical tests that indicate the trustworthiness of these computer analyses, and those which are judged acceptable almost always support the close relationship between animals and fungi.)

Analysis of genes goes beyond using them to reconstruct evolutionary history directly. For instance, there is an insertion into one of the genes used in the replication of DNA, an extra stretch of about fifty nucleotides (the "letters" of DNA's "alphabet"), which is found in animals, fungi, and their close relatives, and nothing else. This might not seem particularly important, but the gene in question is important enough that it is not prone to change easily (in scientific parlance, it is "evolutionarily conserved"), and perhaps more importantly, the insertion is itself conserved. In other words, the same nucleotides (or some obvious derivation of them) are present in the same place in all opisthokonts.

Non-genetic data helps link the two groups as well. The architecture of individual cells in the single-celled relatives of animals and fungi is strikingly similar, both inside and out. This was not apparent until the advent of electron microscopy many of the features that link the two groups are either too small to be seen with a light microscope (the "regular" kind) or are easily overlooked in favour of other, more striking features, many of which (like the cell walls already mentioned) can be taken to imply connections that do not hold up when investigated through other techniques.

These features include the arrangements of the components of the cytoskeleton, a set of protein-based rods and tubes that gives a cell its shape. The arrangement and replication of the flagella is also thought to be a conserved trait. A substantial part of my graduate work is investigating these things while the coherence of the opisthokonts as a group is nowadays almost beyond question, the uniqueness of some of its defining characteristics is simply not known. Electron microscopy has not been around long enough for much data to have been generated, and most of what has been observed focuses on a few well-known organisms. Those organisms that can tell us the most about the relationships of living things are often obscure and poorly studied, a situation that holds perhaps nowhere more strongly than in this case.

But there is one feature that is readily observed and consistent, and that is the number and position of flagella. Like I mentioned, most organisms have flagella at the front ends of their cells, and pull themselves through their surroundings with them opisthokonts are unusual in pushing their cells through their surroundings. Furthermore, most non-opisthokont cells have flagella that appear in twos, or are obviously derived from ancestors that had flagella in twos, while all opisthokonts' flagella appear without any others associated with them. These may not seem like significant things, but one must bear in mind that, when discussing the divergence of animals and plants and fungi, we are discussing the evolution of single-celled organisms. In that context, seemingly unimportant things like the position and number of flagella can be highly significant.

So, classifying something as an opisthokont is not a natural thing for most people. It may seem like an obscure and unimportant distinction. Classifying animals and fungi as each others' closest multicellular relatives has (so far) no known consequences to medicine or agriculture or anything else that most people would notice. But the opisthokont hypothesis is, as far as we can tell, an accurate description of the relationships of living things: it is our best understanding of the relevant facts, and the closest that science can come to the truth.


Taxonomy

Opisthokonts are divided into Holomycota or Nucletmycea (fungi and all organisms more closely related to fungi than to animals) and Holozoa (animals and all organisms more closely related to animals than to fungi) no opisthokonts basal to the Holomycota/Holozoa split have yet been identified. Holomycota and Holozoa are composed of the following groups.

  • Holomycota
      • including chytrids (previously thought to be protists)
      • including microsporidia (previously thought to be protists)
      • shu jumladan Hyaloraphidium (previously thought to be a green alga, now thought to be a chytrid)
      • excluding oomycetes (water molds) (now thought to be stramenopiles)
      • excluding labyrinthulomycetes (slime nets) (now thought to be stramenopiles)
      • excluding myxomycetes (now thought to be amoebozoans)
          (capsasporid amoebae) (ministeriid amoebae)
    • including Myxozoa (previously thought to be protists)

    The paraphyletic taxon Choanozoa includes either non-animal holozoans, or non-animal, non-fungi opisthokonts.

    The choanoflagellates have a circular mitochondrial DNA genome with long intergenic regions. This is four times as large and contains two times as many protein genes as do animal mitochondrial mitochondria.

    Corallochytrium seem likely to be more closely related to the fungi than to the animals on the basis of the presence of ergosterol in their membranes and being capable of synthesis of lysine via the AAA pathway.

    The ichthyosporeans have a two amino acid deletion in their elongation factor 1 α gene that is considered characteristic of fungi.

    The ichthyosporean mitochondrial genome is >200 kilobase pairs in length and consists of several hundred linear chromosomes that share elaborate terminal-specific sequence patterns.



Izohlar:

  1. Kobi

    Buni qayerdan topsam bo'ladi?

  2. Munir

    Beshta imkoniyat

  3. Maccormack

    Kechirasiz, lekin mening fikrimcha, ular noto'g'ri edi. Menga PM orqali yozing, muhokama qiling.

  4. Maular

    Bu shartlilik, ko'p emas, kam emas

  5. Napayshni

    Faqat tog'lar tog'lardan tik bo'lishi mumkin - nega o'zini ko'rsatish kerak?



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