Gene Expression: Translation Part 2

Question 1

What is the Shine-Dalgarno sequence?

Answer 1

ribosome binding site; upstream regulatory sequence that is essential for initiation

Question 2

What are the three stages of transcription?

Answer 2

initiation, elongation, and termination

Question 3

What is a basic summary of initiation of transcription?

Answer 3

small ribosomal subunit binding two initiation proteins and the mRNA transcript followed by the binding of the first aminacyl-tRNA, an initiation factor, and the large subunit of the ribosome

Question 4

What is the initiator tRNA?

Answer 4

first aminoacyl-tRNA that is hydrogen bonded to the start codon

Question 5

What happens to the initiation factors prior to elongation of transcription?

Answer 5

they all dissociate from the initiation complex

Question 6

What is a basic summary of elongation of transcription?

Answer 6

1. second aminoacyl-tRNA enters the A site and hydrogen bonds to the second codon
2. peptidyl transferase activity of the large subunit catalyzes the formation of the peptide bond between the two amino acids
3. translocation = empty tRNA moves to the E site, tRNA #2 moves to the P site, and the next codon moves to the A site

Question 7

When does termination of transcription occur?

Answer 7

when a stop codon appears in the A site and a release factor enters the A site

Question 8

What are the three major differences between eukaryotic and prokaryotic translation?

Answer 8

eukaryotic ribosome is larger, mRNA must be processed before it can be translated, and N-terminal amino acid is different

Question 9

What is the equivalent to the Shine-Dalgarno sequence for eukaryotic translation?

Answer 9

5’ UTR sequences; Kozak sequence

Question 10

What is the eukaryotic translocase called?

Answer 10

eEF-2

Question 11

What is cap-dependent translation?

Answer 11

eukaryotic translation that starts at the 5’ end of the mRNA

Question 12

What is cap-independent translation?

Answer 12

eukaryotes are sometimes capable of starting translation in the middle of an mRNA molecule

Question 13

What is required for the transcript to have for cap-independent translation?

Answer 13

IRES = internal ribosome entry site

Question 14

What is the function of most IRES in eukaryotes?

Answer 14

ensure the cell can make essential proteins when under sub-optimal growth conditions