Biochem 75

Question 1

Protein synthesis is initiated by hydrolysis of what molecule?

Answer 1

GTP

Question 2

What is the role of initiation factors in protein synthesis initiation?

Answer 2

Help assemble ribosomal subunit (40s euk) with the initiator tRNA and are released when the mRNA and the ribosomal 60S subunit assemble with the complex.

Question 3

During the elongation phase of protein synthesis, what binds to the A site?

Answer 3

Aminoacyl- tRNA (except for initiator methionine)

Question 4

What is the role of ribozyme (rRNA) during the elongation phase of protein synthesis?

Answer 4

1) Catalyzes peptide bond formation

2) Transfers growing polypeptide to amino acid in A site

Question 5

Describe translocation within the elongation phase of protein synthesis

Answer 5

Peptidyl tRNA moves to P site

Question 6

What is trimming?

Answer 6

Posttranslational modification where N or C terminals propeptides are removed from zymogen to generate mature protein

Question 7

Which posttranslational modifications are covalent alterations? (6)

Answer 7

1) Phosphorylation
2) Glycosylation
3) Hydroxylation
4) Methylation
5) Acetylation
6) Ubiquitination

Question 8

What are chaperone proteins? Example?

Answer 8

Intracellular proteins involved in facilitating and/or maintaining protein folding

e.g. Heat shock proteins in yeast (Hsp60) that are expressed at high temperatures to prevent denaturation.