Cov Qauv thiab Kev Ua Haujlwm ntawm Ribosomes
Ribosomes yog ib qho ntawm cov organelles tseem ceeb tshaj plaws hauv cov cell, ua lub luag haujlwm ncaj qha hauv kev tsim cov protein. Cov protein yog cov molecules tseem ceeb uas muaj lub luag haujlwm rau yuav luag txhua yam haujlwm ntawm lub cev, los ntawm kev tsim cov qauv cell, ua kom cov tshuaj lom neeg sai dua los ntawm cov enzymes, tswj cov signaling intercellular, thiab pab txhawb kev tiv thaiv ntawm lub cev. Yog li ntawd, kev nkag siab txog cov qauv thiab kev ua haujlwm ntawm ribosomes txhais tau tias kev nkag siab txog ib qho ntawm cov chaw ntawm lub neej ua haujlwm ntawm qib molecular.
Kev Nkag Siab Txog Ribosomes
Ribosomes yog cov macromolecular complexes uas muaj ribosomal RNA (rRNA) thiab ribosomal proteins. Ribosomes pom muaj nyob rau hauv txhua hom cell—ob qho tib si prokaryotes (xws li cov kab mob) thiab eukaryotes (xws li tsiaj txhu, nroj tsuag, thiab fungi). Qhov tshwj xeeb ntawm ribosomes nyob rau hauv lawv cov qauv: rRNA tsis yog tsuas yog ib qho khoom siv xwb tab sis kuj ua lub luag haujlwm catalytic hauv kev tsim cov peptide bonds. Hauv lwm lo lus, ribosomes tuaj yeem xav txog tias yog cov "tshuab" biological uas txhais cov ntaub ntawv genetic los ntawm mRNA mus rau hauv cov amino acid sequences uas ua cov protein.
Cov Qauv Tseem Ceeb ntawm Ribosomes
Feem ntau, ribosomes muaj ob lub subunits: ib lub subunit me thiab ib lub subunit loj. Ob lub subunits no koom ua ke thaum lub sijhawm txhais lus (mRNA txhais lus) thiab sib cais thaum tsis ua haujlwm. Txhua lub subunit yog tsim los ntawm rRNA thiab protein hauv cov feem tshwj xeeb.
Ribosomes hauv Prokaryotes (70S)
Hauv cov hlwb prokaryotic, cov ribosomes tau hais tias muaj qhov loj 70S (S yog ib chav Svedberg uas qhia txog qhov nrawm ntawm kev sib xyaw thaum lub sijhawm centrifugation, tsis yog qhov ntsuas ncaj qha ntawm qhov ntev). 70S ribosomes muaj cov hauv qab no:
- Lub subunit me me 30S, uas muaj 16S rRNA thiab ntau cov protein.
- Lub subunit loj 50S, uas muaj 23S thiab 5S rRNA thiab ribosomal proteins.
Lub subunit me me ua lub luag haujlwm tseem ceeb hauv kev lees paub mRNA thiab txiav txim siab qhov chaw pib ntawm kev txhais lus, thaum lub subunit loj yog qhov chaw tseem ceeb ntawm kev tsim peptide bond.
Ribosomes hauv Eukaryotes (80S)
Hauv cov hlwb eukaryotic, ribosomes yog 80S loj, muaj cov hauv qab no:
- Lub 40S subunit me me, uas muaj 18S rRNA.
– Lub subunit loj 60S, uas muaj 28S, 5.8S, thiab 5S rRNA.
Eukaryotic ribosomes feem ntau yog cov nyuab dua, muaj ntau cov protein ribosomal thiab lwm yam uas tswj cov txheej txheem txhais lus.
Qhov Chaw ntawm Ribosomes hauv Cells
Ribosomes tuaj yeem pom muaj nyob rau hauv ob qhov chaw tseem ceeb:
1. Cov ribosomes dawb hauv cytoplasm
Feem ntau cov ribosomes dawb ua cov protein uas yuav siv rau hauv cytosol, piv txwv li cov enzymes metabolic lossis cov protein ntawm lub cell.
2. Ribosomes raug khi rau ntawm qhov rough endoplasmic reticulum (rough ER)
Cov ribosomes uas txuas rau ntawm ER feem ntau tsim cov protein kom raug tso tawm ntawm lub cell, ntxig rau hauv lub cell membrane, lossis xa mus rau cov organelles tshwj xeeb xws li lysosomes. Ribosomes txuas vim tias ER muaj cov receptors uas cuam tshuam nrog ribosomes thaum cov saw polypeptide uas tsim tawm muaj cov teeb liab tshwj xeeb (cov teeb liab peptide).
Tsis tas li ntawd xwb, cov organelles xws li mitochondria thiab chloroplasts kuj muaj lawv tus kheej ribosomes, uas zoo ib yam li prokaryotic ribosomes (70S). Qhov no txhawb nqa txoj kev xav endosymbiosis, uas hais tias mitochondria thiab chloroplasts tau los ntawm cov kab mob prokaryotic uas nyob ua ke hauv cov hlwb ntawm cov poj koob yawm txwv eukaryotic.
Cov Cheebtsam Ribosome: rRNA thiab Protein
Ribosomes muaj ob lub ntsiab tseem ceeb:
– Ribosomal RNA (rRNA): Qhov no yog hom RNA tseem ceeb thiab tsim lub moj khaum thiab chaw ua haujlwm ntawm ribosome. rRNA yog lub luag haujlwm rau kev ua kom muaj cov peptide bonds (peptidyl transferase activity).
- Cov protein Ribosomal: ua haujlwm los tswj cov qauv ntawm rRNA, pab sib sau ua ke cov subunits, thiab cuam tshuam nrog cov yam ntxwv txhais lus.
Kev sib xyaw ua ke ntawm rRNA thiab cov protein tsim cov qauv peb-seem tseeb, tso cai rau ribosomes ua haujlwm sai thiab raug.
Cov Chaw Ua Haujlwm Hauv Ribosomes
Thaum lub ribosome tab tom txhais lus, muaj peb qhov chaw tseem ceeb uas tseem ceeb heev, tshwj xeeb tshaj yog nyob rau ntawm lub subunit loj:
1. Qhov Chaw A (Aminoacyl site)
Qhov chaw nkag rau tRNA uas nqa cov amino acids raws li mRNA codon.
2. P qhov chaw (Peptidyl qhov chaw)
Qhov chaw ntawm tRNA nqa cov saw polypeptide uas loj hlob tuaj.
3. Qhov Chaw E (Qhov Chaw Tawm)
Qhov chaw uas tRNA uas tau tso tawm cov amino acids tawm mus.
Kev txav ntawm tRNA los ntawm A mus rau P thiab tom qab ntawd mus rau E tshwm sim thaum ribosome "nyeem" mRNA peb lub hauv paus ib zaug (codon los ntawm codon).
Kev Ua Haujlwm ntawm Ribosomes hauv Protein Synthesis
Lub luag haujlwm tseem ceeb ntawm ribosomes yog txhais lus, uas txhais cov kab ke nucleotide hauv mRNA mus rau hauv cov kab ke amino acid. Kev txhais lus feem ntau muab faib ua peb theem:
1. Kev pib
Nyob rau theem no, lub subunit me me ntawm ribosome txuas rau mRNA thiab nrhiav qhov pib codon (feem ntau yog AUG). Lub initiator tRNA uas nqa methionine kuj koom nrog. Thaum lub pib codon nyob rau hauv qhov chaw, cov subunits loj sib sau ua ke los tsim ib lub ribosome uas ua haujlwm.
2. Kev ntev
Tus ribosome txav mus raws mRNA, ua rau txoj saw polypeptide ntev zuj zus. Tus tRNA uas nqa cov amino acid nkag mus rau hauv qhov chaw A, qhov chaw uas nws txuas nrog txoj saw hauv qhov chaw P. Tus ribosome mam li txav ib lub codon, tshem tawm tRNA thiab ua chaw rau tRNA tom ntej.
3. Kev xaus
Thaum lub ribosome ntsib ib lub codon nres (UAA, UAG, lossis UGA), tsis muaj tRNA sib phim rau lub codon ntawd. Hloov chaw, ib qho termination factor nkag mus thiab ua rau muaj kev tso tawm ntawm cov saw polypeptide. Lub ribosome ces dissociates ua ob lub subunits thiab npaj txhij rau kev siv dua.
Ribosomes ua cov tshuaj tua kab mob
Cov ribosomes prokaryotic txawv ntawm cov ribosomes eukaryotic. Qhov sib txawv no siv rau hauv kev kho mob vim tias qee cov tshuaj tua kab mob tuaj yeem tiv thaiv cov ribosomes kab mob yam tsis muaj kev puas tsuaj rau tib neeg cov ribosomes. Piv txwv li:
– Tetracycline tiv thaiv tRNA nkag mus rau hauv A site.
- Chloramphenicol inhibits peptidyl transferase kev ua haujlwm.
– Streptomycin tuaj yeem ua rau nyeem tsis raug ntawm mRNA.
Txawm li cas los xij, kev siv cov tshuaj tua kab mob yuav tsum tsim nyog vim tias cov kab mob tuaj yeem tsim kev tiv thaiv los ntawm kev hloov pauv lossis lwm yam kev tiv thaiv.
Xaus
Ribosomes yog cov organelles tseem ceeb uas ua haujlwm ua qhov chaw ntawm kev tsim cov protein. Cov qauv ribosome muaj ob lub subunits, ib qho loj thiab ib qho me, nrog rau cov khoom tseem ceeb yog rRNA thiab ribosomal proteins. Ribosomes muaj A, P, thiab E qhov chaw, uas ua kom muaj kev txiav txim siab thiab raug cov txheej txheem txhais lus. Dhau li ntawm kev ua lub luag haujlwm tseem ceeb hauv kev tsim cov protein rau cov kev xav tau ntawm tes, ribosomes kuj tseem raug tsom los ntawm ntau yam tshuaj tua kab mob vim muaj qhov sib txawv ntawm prokaryotic thiab eukaryotic ribosomes. Los ntawm kev nkag siab txog cov qauv thiab kev ua haujlwm ntawm ribosomes, peb tuaj yeem pom tias cov txheej txheem tseem ceeb uas txhawb nqa lub neej nyuaj npaum li cas thiab sib koom tes.
