DNA translation Flashcards
what is translation
the synthesis of a linear chain of amino acids (primary transcript)
what does translation require
aminoacyl-tRNA
ribosomes
mRNA
what is the site of translation
ribosomes
functional 80S ribsomoe is composed of what
2 subunits
what subunits are contained by a large 60S subunit
5S rRNA- 120 nucleotides
28S rRNA- 2,700 nucleotides
5.8S rRNA- 160 nucleotides
about 49 ribosomal proteins
what does a small 40S subunit contain
18S rRNA
about 33 ribosomal proteins
what fit together to form a cleft
the 2 irregularly shaped subunits (40S and 60S)
how do the mRNA and cleft interact
mRNA moves through the cleft as the ribosome passes along the mRNA during translation
where is mRNA bound
to the small 40S subunit
how many binding sites does the 60S subunit contain
2
what are the binding sites on the 60S subunit called
P site and A site
what is the purpose of the P site on the 60S subunit
growing polypeptide chain is bound to this site (peptidyl-tRNA site)
what is the purpose of the A site on the 60S subunit
new aminoacyl-tRNA to be added to growing polypeptide chain is bound at this site (aamino-tRNA site)
what does translation proceed from and to
N-terminus to C-terminus of protein
what direction is mRNA read in
5/ to 3/
how many ribosome can be bound and translated to mRNA at the same time
more than one
what is translation also known as
protein synthesis
how does chain elongation occur
by addition of amino acids to C-terminal of the polypeptide bound to the ribosome
what happens during the initiation phase in relation to proteins
begins with the binding of the initiation protein eIF3 to the 40S ribosomal subunit
this protein acts as an anchor for other initiation proteins which ultimately bind the mRNA to the 40S ribosomal subunit
eIF3 binds another protein, called eIF4G which contains two further protein binding sites on it
eIF4G binds ployA binding protein (PAB)
PAB is bound to the polyadenylated 3/-end of the mRNA molecule
what proteins are involved in the initiation phase
eIF3, eIF4G, PloyA binding protein
what happens in the initiation phase after the protein binding
once bound to the 40S ribosomal subunit, the mRNA nucleotide sequence is scanned from the 5/ end until the initiation codon sequence is encountered (5/-AUG)
the 60S ribosomal subunit is attached to the 40S ribosomal subunit forming the initiation complex. the methionine-tTRNA occupies the P site
what happens during elongation
aminoacyl-tRNA occupies A site
A peptide bond is now formed between the 2 amino acids in the P and A site
transfer of amino acid occupying P site onto aminoacyl-tRNA occupying A site
a-amino group of amino acid in A site attacks carboxyl group of amino acid in P site, displacing bond with tRNA at P site
what happens during translocation
ribosome moves one codon towards 3/-end of mRNA. movement requires the action of a translocase (elongation factor)
movement shifts anticodon of peptidyl-tRNA occupying A site into P site and and tRNA occupying P site is released
A site is now empty, awaiting new aminoacyl-tRNA
what are the 3 termination sequences
UAA
UAG
UGA
what happens when a termination sequence occurs
it is recognized by a release factor called eRF
what 3 things does eRF do
hydrolyses terminal peptidyl-tRNA bond
releases free polypeptide and tRNA from the P site
Ribosome dissociates into 40S and 60S subunits
what are the 4 phases of translation
initiation
elongation
translocation
termination
