translation

Question 1

what is translation?

Answer 1

Use of mRNA to direct protein synthesis and the subsequent post-translational processing of the protein molecule

Question 2

Briefly explain the steps of translation

Answer 2

DNA in the nucleus serves as a template

mRNA processed before leaving nucleus

mRNA has codons when formed

mRNA moves into cytoplasm and becomes associated with ribosomes

tRNA with anticodon carries amino acids to mRNA

Anticodon-codon complementary base pairing occurs

Peptide chain transferred from resident tRNA to incoming tRNA

tRNA departs to pick up another amino acid

Question 3

Which amino acid do all polypeptides begin with and why?

Answer 3

Methionine

All mRNA molecules begin with AUG codon

Question 4

Which amino acid do all polypeptides begin with and why?

Answer 4

Methionine

All mRNA molecules begin with AUG codon

Question 5

What are the 3 stop codons?

Answer 5

UAA

UAG

UGA

Question 6

Name the 3 stages of translation

Answer 6

Initiation

Elongation

Termination

Question 7

What happens during the initiation stage of translation?

Answer 7

Assembly of 3 components that carry out the process (ribosome, tRNA and mRNA)

Question 8

What happens during the elongation stage of translation?

Answer 8

Stepwise addition of amino acids to the protein chain

Question 9

What happens during the termination stage of translation?

Answer 9

stop codon encountered

Dissociation triggered

Question 10

What are the 3 slots for tRNAs in a large ribosomal subunit (50S)?

Answer 10

Aminoacyl-tRNA (A)

Peptidyl-tRNA (P)

Exit (E)

Question 11

Describe the common features of tRNA

Answer 11

D and T arms

Acceptor stems (3’ end)

Anticodon (read 3’ to 5’)

Wobble position 5’ end of anticodon

Question 12

what do small ribosomal subunits (30S) contain?

Answer 12

mRNA binding site

Question 13

What is the function of aminoacyl-tRNA synthetases?

Answer 13

Specific for each amino acid

Recognise only the amino acid and the tRNA for that amino acid

Uses ATP

Proofreading ability

Question 14

Explain what happens during the initiation stage of translation

Answer 14

Complex of small ribosomal subunit and initiator tRNA binds to 5’ cap (UAC anticodon)

Complex moves along mRNA in 3’ direction scanning for AUG start codon

tRNA molecules bind to codon via anticodon

Large ribosomal subunit aligns to tRNA molecule at P site and forms complex with small subunit

Question 15

Explain what happens during the elongation stage of translation

Answer 15

Second tRNA molecule pairs with next codon in ribosomal A site

Amino acid in P site covalently attached via peptide bond to amino acid in A site

tRNA in P site deacetylated (no amino acid) while tRNA in A site carries peptide chain

Ribosome moves along mRNA strand by one codon position (5’ to 3’)

Deacetylated tRNA moves into E site and released

tRNA carrying peptide chain moves to P site (translocation)

New tRNA attaches to next codon in A site