Mod 7 - From RNA to Protein
暂无描述。系统推荐的高质量记忆内容，适合每天坚持背诵学习。
卡片预览 (24 张)
What is translation?
protein synthesis - conversion from mRNA to a protein
what is a codon?
3 nucleotide (triplet) code used to specify amino acids
what is the function of aminoacyl tRNA snythetase?
• each tRNA is recognised by 1 of 20 aminoacyl tRNA synthetases • some tRNAs recognise more than 1 codon
how does one tRNA recognise more than one codon?
wobble - allows unconventional base pairing between third base in codon and first base in anticodon - e.g. G-U base pairing - e.g. inosine (guanine) can pair with A, C, and U
what are the 3 stages of protein synthesis?
• initiaiton • elongation • termination
what are some of the prerequisites for protein synthesis?
• machinery (ribosomes or cofactors) • Energy (e.g. ATP or GTP)
what kind of ribosomes do eukaryotes and prokaryotes have?
• euk = 80s ribosomes -prok = 70s ribosomes
What are the 2 ribosomal subunits in prokaryotes?
• 50s subunit • 30s subunit
What are the 2 ribosomal subunits in eukaryotes?
• 60s • 40s
why does 2 + 2 not necessarily equal 4? (ribosomal)
• measure of S is svedberg - a measure of shape as well as size
How are amino acids activated? (start of protein synthesis)
• amino acids couples with ATP molecule (transesterification) • forms aminoacylAMP • aminoacyl segment couples with tRNA 2 step process - AA + ATP -> AA-AMP + PP - AA-AMP + tRNA -> AA-tRNA + AMP
what is a shine-dalgarno sequence?
• a sequence of bases with methionine (start codon) embedded • known as Kozak sequence in eukaryotes
what are the molecules involved with initiation of translation?
• specific initiator methionine tRNA • initiation factor 2 (IF2) - covalently bonded to GTP (known as a G protein) • 30s ribosomal subunit bonded to IF1 and IF3 • mRNA containing an AUG (within a shine-dalgarno sequence) • large subunit of ribosome (including P site and A site)
what are the steps in initiation of translation?
• IF2 G protein couples with 30s subunit • initiator tRNA (with formylmethionyl) couples with mRNA • large subunit assembles with the newly formed complex to complete initiation complex side effects - ATP -> ADP - GTP -> GDP (still bound to IF2 but becomes hydrolysed)
what is the function of IF1 ?
blocks A site on large subunit to tRNA-met, inhibits premature 30S-50S interaction
What is the function of IF2 ?
tags tRNA and regulates entry into ribosome
What is the function of IF3 ?
• inhibits premature 30S-50S interaction • stabilises free 30S • accuracy check for tRNA-met binding
what is the elongation factor required for the elongation step called?
aminoacyl tRNA-EFTu-GTP (is a G protein because it is bound to GTP)
what is special about tRNA-Met i?
• the only tRNA which can bind to the P site • P site = peptidyl-tRNA site - peptide bond formation
what is the function of EFTu-GTP?
• lines up the next amino acid on the A site next to the first methionine • causes ejection of EFTu-GDP (hydrolyses) A site = aminoacyl-tRNA site (acceptor site) - where incoming aminoacyl-tRNA binds
what happens after the second amino acid is placed on the mRNA?
• ribosome translocates from having its P site on AA 1 to AA2, and having its A site on AA2 to AA3 (translocates whole molecule one amino acid downstream) • this means peptidyl tRNA is now in P site, A site is free
what is the function of the different elongation factors?
• EF-Tu = mediates aminoacyl-tRNA entry to ribosome • EF-G = mediates translocation of ribosome
How does termination occur?
• when a termination codon (UAA, UGA, UAG) appears, a release factor (RF-GTP) binds to the A site • when RF is bound, hydrolysis of polypeptide chain from tRNA occurs • ribosome then dissociates from polypeptide
what is the role of GTP?
• GTP = guanosine triphosphate • provides energy via hydrolysis - GTP -> GDP + Pi