Translation

Question 1

What is an aminoacyl tRNA synthetase?

Answer 1

protein enzyme that put the right amino acid on the right tRNA.

Question 2

What are the start & stop codons?

Answer 2

Start = AUG (codes for Met)
Stop = UAA, UAG, UGA

Question 3

What is degeneracy and why is it good?

Answer 3

64 codons and only 20 AAs. Multiple codons making a single AA means a mutation is that much less likely to cause a catastrophic change.

Question 4

Identify the important differences between bacterial and eukaryotic translation, especially in regard to initiation

Answer 4

1. In bacteria, SD sequence facilitates binding of ribosome right at start site.
2. In eukaryotes, eIF4E binds the 7-methyl-guanosine cap on 5’ end. Other eiFs bind and then the small ribosomal subunit. It scans down the mRNA until it hits AUG. Large subunit binds. Initiation achieved
3. Alternately, an IRES can be used to attract ribosome instead of a cap

Question 5

Explain the significance and effects of cap-independent initiation

Answer 5

An IRES element in RNA can be used to recruit the ribosome and initiate translation (no need for a cap). Viral RNAs often take advantage of this. Some cellular RNAs use this too (mostly stress-related; cell shuts down cap-related form, switch to IRES)

Question 6

Explain the significance and effects of mRNA editing

Answer 6

mRNAs can be edited after they’re made, leading to the same mutations that cause problems (nonsense, missense)

Question 7

Explain the significance and effects of eIF2-alpha phosphorylation

Answer 7

eIF2alpha is critical for the steps that lead to binding of the initiator tRNA to the ribosome. When eIF2-alpha is phosphorylated, its activity is inhibited and this blocks initiation. eIF2-alpha can be phosphorylated by several pathways. One is induced by interferon (made when cell has a virus). Other cellular stresses can do this too

Question 8

How does Rapamycin work?

Answer 8

phosphorylates 4E-BP so that the initiation complex cannot be formed, downregulating translation.

Question 9

What are the 3 classes of antibiotics?

Answer 9

Aminoglycoside: disrupt proofreading so more errors are made
Tetracycline: block the A site
Macrolide: inhibit elongation of the protein by preventing peptidyltransferase from forming peptide bonds between the amino acids.
Some (like azithromycin) block the E site = constipation

Question 10

Describe iron regulation in a cell.

Answer 10

TFR gets Iron into the cell
Low Fe: A protective IRE-BP binds an IRE element on TFR mRNA and protects it from degradation so TFR is made
High Fe: Fe binds IRE-BPs, inhibiting their ability to protect the TFR mRNA. It gets degraded, so less TFR is made

Ferritin binds Fe when conc are high to prevent toxicity
Low Fe: IRE-BP binds and prevents translation
High Fe: IRE-BP is inhibited and cannot bind, so Ferritin is translated