Protein synthesis Flashcards
what is the central dogma?
trasnfer of information from DNA to RNA to transcription to translation
what is the coding region?
the central portion of the mRNA that is translated into a protein
which side is capped and which side is polyadenylated?
5’ primer capping
3’ primer polyadenylation
what are ribosomes comprised of?
protein and RNA
where does protein synthesis take place?
in a cleft between the large and small subunit
at what rate do ribsomes work on a polypeptide chain?
20 amino acids are added per second to a polypeptide chain
protein turnover is rapid so what is cellular abundance of the different tyoes of ribosomes?
rRNA - 85%
tRNA - 15%
mRNA - 5%
which subunits do mammalian ribosomes consist of?
40S and 60S subunits which together make 80S (not 100S as s stands for Svedburg which is a unit for the sedimentation rate (not linear))
what is the structure of the 80S subunit?
Top has a peptidyl binding site (P site) and the large subunit 60S
bottom has an aminoactyl tRNA binding site (A site) and exit (E site)
translation (initiation)
Assembly of ribosomes on mRNA together with the first initiator tRNA (aminoacyl tRNA / met-tRNAi)
Multiple initiation factors which associate with different elements of the RNA such as cap (cap binding proteins) or poly A tail (poly A binding proteins) and so binds the initiation factors (EIF3) Prevents association of 40S back to 60S Forms a complex One initiation factor(EIF2), associated with the 40s subunit, also binds with met-tRNAi (which is already binded to GTP), this complex is known as the ternary complex The both complexes formed bind on the ribosomal sub unit to form the 43s ribosomal sub unit, binds at the P site Which then combine to form the 48s pre initiation complex so the RNA is now associated with the small ribosomal sub unit with the various initiation factors already bound to it The RNA translocates along the ribosomal sub unit and causes the consumption and breakdown of ATP into ADP and Pi As each base is translocated one ATP is consumed Process is called scanning
translation (elongation)
Initiator tRNA is in P site
tRNA with complimentary anticodon goes to A site due to close proximity of amino acids in site P and A, a peptide bond is formed between them the ribosome moves along by another codon the empty tRNA goes to E site and is released the other tRNA (previously in A site) now holds onto peptide chain and is in the P site. Now referred to as peptidal RNA
translation (termination)
Stop signal UAG in A site
No tRNA will have a complimentary anticodon to UAG codon This codon is recognized by a protein (release factor) Hydrolysis of terminal peptidyl-tRNA Polypeptide is released
