Translation lecture 1

Question 1

what is a missense mutation ?

Answer 1

substitution of one nucleotide so that one an alternative amino acid is incorporated into the polypeptide

Question 2

nonsense mutation ?

Answer 2

substitution of one nucleotide so that a stop codon is prematurely introduced, and this results in early termination of of the polypeptide

Question 3

frameshift mutation

Answer 3

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

Question 4

ribosomal RNA that have catalytic activity are known as

Answer 4

ribozymes

Question 5

new amino acids are attached to what terminus of the growing polypeptide chain

Answer 5

c terminus

Question 6

what transcribes tRNA

Answer 6

RNA pol 3, its own internal promoter

Question 7

what terminal sequence is found at the 3’ end of tRNA

Answer 7

CCA added after tRNA is processed

Question 8

what carries out the aminoacylation of tRNA

Answer 8

Aminoacyl-tRNA sythetases

Question 9

what links the amino acid to the tRNA molecule

Answer 9

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

Question 10

can the ribosome recognise whether the correct amino acid is bound to the tRNA

Answer 10

no

Question 11

each tRNA synthetase is specific to how many amino acids ?

Answer 11

only 1

Question 12

what are different tRNA molecules that attach the same amino acid called ?

Answer 12

isoacceptor tRNA molecules

Question 13

where is the wobble position found

Answer 13

nucleotide at 5’ (wobble) first position of anticodon and nucleotide at 3’ position of codon (3rd position)

Question 14

in prokaryotes, transcription is

Answer 14

co-transcriptional

Question 15

what is the name of the sequence found 7-9 nucleotides upstream of the initiation codon AUG

Answer 15

the shine dalgarno sequence, not found immediately upstream of internal methionine codons. positions the initiation codon at the P site on the ribosome

Question 16

what is positioned at the P site

Answer 16

the growing polypeptide is covalently attached to the tRNA at the peptide site

Question 17

A site

Answer 17

aminoacyl site - where a second amino-acyl is bound

Question 18

what role do IF-3 and IF-1 carry out ?

Answer 18

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.

Question 19

describe another function of IF-3

Answer 19

helps position fMet-tRNA and the initiation codon at the p site of the ribosome

Question 20

IF-2-GTP

Answer 20

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.

Question 21

how does the ribosome interact with mRNA ?

Answer 21

30s complex recognises the Shine-dalgarno sequence and the initiation codon

Question 22

what role does IF-1 play ?

Answer 22

binds to the 30S subunit and facilitates the actions of IF-2 and IF-3. It is associated with IF-2

Question 23

what causes IF-3 to be displaced from the e site ?

Answer 23

binding of fmet-tRNA to the p site.

Question 24

what happens after the IF-3 is ejected from the e site ?

Answer 24

50s subunit assembles with 30s initiation complex. IF-2 hydrolyses GTP to GDP and Pi. It is then released along with IF-1.