Translation lecture 1 Flashcards
what is a missense mutation ?
substitution of one nucleotide so that one an alternative amino acid is incorporated into the polypeptide
nonsense mutation ?
substitution of one nucleotide so that a stop codon is prematurely introduced, and this results in early termination of of the polypeptide
frameshift mutation
a point mutation which results in either the ribosome reading 4 nucleotides as three, o backing up one nucleotide and reading from a different reading frame
ribosomal RNA that have catalytic activity are known as
ribozymes
new amino acids are attached to what terminus of the growing polypeptide chain
c terminus
what transcribes tRNA
RNA pol 3, its own internal promoter
what terminal sequence is found at the 3’ end of tRNA
CCA added after tRNA is processed
what carries out the aminoacylation of tRNA
Aminoacyl-tRNA sythetases
what links the amino acid to the tRNA molecule
an ester linkage between the carboxylate group of the amino acid and a hydroxyl group of the ribose of an adenylate residue at the 3’ end of the tRNA molecule
can the ribosome recognise whether the correct amino acid is bound to the tRNA
no
each tRNA synthetase is specific to how many amino acids ?
only 1
what are different tRNA molecules that attach the same amino acid called ?
isoacceptor tRNA molecules
where is the wobble position found
nucleotide at 5’ (wobble) first position of anticodon and nucleotide at 3’ position of codon (3rd position)
in prokaryotes, transcription is
co-transcriptional
what is the name of the sequence found 7-9 nucleotides upstream of the initiation codon AUG
the shine dalgarno sequence, not found immediately upstream of internal methionine codons. positions the initiation codon at the P site on the ribosome
what is positioned at the P site
the growing polypeptide is covalently attached to the tRNA at the peptide site
A site
aminoacyl site - where a second amino-acyl is bound
what role do IF-3 and IF-1 carry out ?
bind to the 30S subunit, preventing the premature assembly of the 70S complex. IF-3 bind to the exit site on the ribosome, and IF-1 is positioned at the A site.
describe another function of IF-3
helps position fMet-tRNA and the initiation codon at the p site of the ribosome
IF-2-GTP
GTPase that binds to the 30s subunit, IF-2-GTP complex specifically recognises the initiator tRNA and facilitates binding of Met-tRNA to the p site. fmet-tRNA is only one that fits the p site.
how does the ribosome interact with mRNA ?
30s complex recognises the Shine-dalgarno sequence and the initiation codon
what role does IF-1 play ?
binds to the 30S subunit and facilitates the actions of IF-2 and IF-3. It is associated with IF-2
what causes IF-3 to be displaced from the e site ?
binding of fmet-tRNA to the p site.
what happens after the IF-3 is ejected from the e site ?
50s subunit assembles with 30s initiation complex. IF-2 hydrolyses GTP to GDP and Pi. It is then released along with IF-1.
