Topic 13.3: Translation Flashcards
how many rRNA and protiens do prokaryotes and eukaryotes have
prokaryotes - 3 rRNA and many proteins
eukaryotes - 4 rRNA and many proteins
what subunits of ribosome are there in prokayrotes and eukaryotes
prokaryotes - 30S + 50S subunits = 70S ribosome
eukaryotes - 40S + 60S subunits = 80S ribosome
what is required for translation
adaptor molecule = tRNA template = mRNA enzyme = rRNA in ribsomes substrates = activated amino acids SO tRNA with activated amino acids initiation factors, elongation factors, release factors, and energy (GTP/ATP)
what are some key features of genetic code
triplet code - 3 base pairs = amino acid
degenerate = more than one triplet code (codon) for same amino acid
non overlapping and ‘comma less’ - no gaps
what is a key feature of translation
5 to 3 prime end template read through to produce N to C polypeptide chain extension
what is the initiation codon
AUG
what is the termination codon
UAA, UAG, UGA
whjat is the role of tRNA
each tRNA can bind an amino acid to its 3 prime end (as it can be charged with an activated amino acid)
each tRNA has an anticodon to recognise a complementary codon in mRNA
how do tRNA become charged and attached to activated amino acids
Aminoacyl-tRNA synthetase will recognize a specific amino acid and then binds to ATP to charge amino acid
the same enzyme will then recognize a specific tRNA using anticodon and binds specific amino acid to specific tRNA to form a charged tRNA with aminoa cid attached
what happens during initiation of translation
mature mRNA has 5 prime CAP and initiation codon (AUG)
- the cap is recognized by cap binding proteins, which along with initiation factors, small ribosome and energy, the tRNA-methionine (amino acid activated) become attached
- the complex moves across mRNA until it reaches AUG which is recognized by the anticodon on P site of tRNA-amino acid complex (needs energy)
- initiation factors are lost and a large subunit is being recruited (functional ribsoome subunit ready). so results in tRNA-methionine complex bound to AUG initiation codon and a functional ribosome assembled
what results from initiation
80s initiation complex with tRNA-methionine in P site of ribosome on AUG on mRNA and empty A site on ribosome ready for elongation
what are the sites called on functional ribosome
E, P, A from 5 to 3 prime end
why is the A site empty
to receive the next tRNA-amino acids complex
what happens during elongation of translation
- the next codon can be recognized at empty A site where binding of aminoacyl-tRNA occurs with its cognate amino acid attached to it (GTP required)
- peptide bond formation occurs catalysed by peptidyltransferase between first amino acid and second one and the first one is thus a uncharged tRNA which is in E site
- translocation occurs - ribosome moves across mRNA (need GTP), one codon at a time from 5 to 3 end.
- the peptidy- tRNA complex moved to P site and empty A site forms so new codon is being freed, the growing polypeptide is ‘pushed’ intp exit tunnel, elongation factors are involved
what results from elongation
peptidyl-tRNA in P site and empty A site ready for next cycle
only 2 sites occupied of EPA