2017 Biochemistry - Protein Synthesis

Question 1

Importance of the 3’ end of tRNA?

Answer 1

Amino Acid binding site

Question 2

Importance of the TYC loop of tRNA?

Answer 2

Where tRNA binds to Ribosome

Question 3

Importance of the D loop of tRNA?

Answer 3

Contains high amounts of dihydrouridine residues (this is recognized by the enzyme tRNA synthetase)

Question 4

Importance of the ANTICODON loop of tRNA?

Answer 4

Contains the Anticodon which is complementary to the codon of the messenger RNA

Question 5

How does tRNA and mRNA bind? Parallel or Antiparallel?

Answer 5

Antiparallel:
tRNA runs: 3’-5’
mRNA read: 5’-3’

Question 6

How does initiation w/ tRNA and the Ribosome work?

Answer 6

1. Initiation factors dissociate the 70S (80S in eukaryotes) into the parts of 50S & 30S (40S & 60S)
2. tRNA-Met and mRNA bind the 40S subunit with the help of eIF2. tRNA-fMet (formyl methionine) is the initiation codon for prokaryotes.
3. The big subunit (60S or 50S) reassemble with the smaller unit and the tRNA-Met introduces the first AA (methionine) into a protein. It binds to the initiation Codon (AUG).

Question 7

What are the 4 Initiation factors for eukaryotes and what do they do?

Answer 7

eIF-1A & eIF-3: bind 40S
eIF-4F: mRNA complex binds to ribosome subunit
eIF-2: (GTP) binds to tRNA-met which binds AUG
eIF-2: lost as GTP is hydrolyzed and 80S unit formed

Question 8

Function of A, P, E sites of Ribosome?

Answer 8

A - Acceptor: accepts incoming tRNA
P - Peptide: site where peptide bond is formed for new tRNA as protein is being constructed.
E - Exit

Question 9

What is required for new peptide bond formation?

Answer 9

Elongation Factor 1A (eEF1A) and 1-GTP

Question 10

What is required for Translocation?

Answer 10

This is the movement of the ribosome one-codon down the mRNA.
Requires:
-eEF2 & GTP

Question 11

What is required for Termination?

Answer 11

Stop codon is reached at the A-site

Releasing factors: eRF1 and eRF3

Question 12

What are the energy requirements for A.A. tRNA activation and for Elongation/Termination?

Answer 12

2 ATP
2 GTP

4 Total high energy bonds

Question 13

What is the importance of signal peptides?

Answer 13

Only in Eukaryotic cells, helps direct Ribosomes to go from cytoplasm to ER, shuttling the protein into the ER for further processing.
Signal Recognition Particle (SRP) - binds to peptide as it is expelled from Ribosome and prevents translation until ribosome docks with ER.
GTP dependent process - Ribosome binding
ATP depended - transport protein through the Ribosome membrane.

Question 14

Name 2 Eukaryotic Protein Synthesis Inhibitors and what they inhibit (specifically)?

Answer 14

Cycloheximide - inhibit peptide bond formation

Diphtheria toxin - catalyze reaction of NAD+ w/ elongation factor, results in inhibition of translocation

Question 15

Name 2 Eukaryotic & Prokaryotic Protein Synthesis Inhibitors and what they inhibit (specifically)?

Answer 15

Chloramphenicol - inhibit peptide bond formation & mitochondrial protein synthesis at high levels
Puromycin - causes premature termination

Question 16

Name 3 Prokaryotic Protein Synthesis Inhibitors and what they inhibit (specifically)?

Answer 16

Tetracycline - inhibits elongation
Streptomycin - blocks translation
Erythromycin - inhibits translocation