Lecture 19

Question 1

What are the initiation factors for prokaryotes?

Answer 1

IF1, IF3

Question 2

what are the elongation factors for prokaryotes?

Answer 2

Ef-Tu/Ts, EF-G (EF1, EF2)

Question 3

what are the termination factors for prokaryotes?

Answer 3

RF1 - RF3

Question 4

what are the initiation factors for eukaryotes?

Answer 4

eIF1 - eIF5

Question 5

what are the elongation factors for eukaryotes?

Answer 5

eEF1, eEF2

Question 6

what are the termination factors for eukaryotes?

Answer 6

eRF1, eRF3

Question 7

what do prokaryotes use to find their initiation sites for translation?

Answer 7

shine-Delgarno box which is generally located 8 base pairs upstream of the start codon

Question 8

what do eukaryotes use to find their initiation sites for translation?

Answer 8

40S ribosomal subunit interaction with 5’ methylated cap of mRNA

Question 9

how does streptomycin disrupt bacterial translation?

Answer 9

binds to the 16S rRNA of the 30S subunit of the bacterial ribosomes and messes up base pairing, causing miscoding during elongation

Question 10

how does puromycin disrupt bacterial translation?

Answer 10

imitates AA-tRNA and causes premature ejaculation of the nascent protein.
- similar to dideoxy sequencing

Question 11

how does diphtheria toxin work?

Answer 11

it is a protein that gets cleaved into two fragments, A and B

• B causes internalization of the toxin
• A is an enzyme that attaches an ADP ribose on eEF2 which poisons translation

Question 12

Why can’t puromycin be used as an antibiotic?

Answer 12

It affects eukaryotes

Question 13

What is a main sign of diphtheria?

Answer 13

Thick grey leathery coating in the throat

Question 14

What is ricin?

Answer 14

It is a protein toxin that is found in castor bean. It is insoluble in castor oil and one bean can kill a child.

Question 15

How does ricin work?

Answer 15

Two chains

1) B gets the toxin within the cell
2) A inactivates a specific A residue on the ribosomes making it nonfunctional.

Question 16

What level do aminoglycoside antibioitics act at?

Answer 16

The level of initiation

Question 17

What level do tetracycline and spectinomycin work at?

Answer 17

The loading step

Question 18

What does chloramphenicol do as an antibiotic?

Answer 18

Acts against peptidyl transferase

Question 19

How much energy does the charging of tRNA consume?

Answer 19

2 ATP

Question 20

How much energy is used every time the ribosomes moves along the codon using elongation factors?

Answer 20

1 GTP

Question 21

How much energy does termination use?

Answer 21

1 GTP

Question 22

How many high energy bonds are utilized for every amino acid polymerized?

Answer 22

4 (ATPs or GTPs)

Question 23

What is the purpose of ferretin protein?

Answer 23

It controls the intracellular concentration of iron by binding to it and titrating it down to appropriate levels.

Question 24

What is the reason eukaryotic mRNA is circular?

Answer 24

The initiator complex binds both the 5’ cap and the 3’ poly A tail. The reason is that when the ribosome begins at the 5’ end of the mRNA it will make its way around the circle like a lap and end back at the initiation complex where it can then restart almost immediately if allowed to.

Question 25

How is ferretin regulated?

Answer 25

There is an Iron Response Element (IRE) located in the 5’ UTR region just before the ferretin mRNA. This IRE is usually in a stem loop that is bound by IRE-Binding Protein. When there is high concentration of iron, the IRE-BP gets bound by iron and releases the IRE stem loop, allow the ferretin mRNA to be translated.

Question 26

Describe what happens in Hereditary Hyperferrinemia - Cataract Syndrome.

Answer 26

There is a mutation in the Iron Response Element that prevents it from being bound in the stem loop conformation and allows perpetual translation of the ferretin protein which eliminates iron and causes cataracts.

Question 27

How is initiator tRNA regulated?

Answer 27

Met-tRNA normally forms a complex with eIF2 and GTP that drops it off at the ribosomes for translation and the GTP in this complex is usually hydrolyzed to GDP. In order for it to start over it first needs to be converted back into GTP by eIF2B.
- BUT if eIF2B is phosphorylates by something, it becomes inactive and initiation can’t begin.

Question 28

What is vanishing white matter and what causes it?

Answer 28

A neurological deterioration exacerbated by head trauma where the white myelin vanishes.
- a mutation in any of the 5 subunits of eIF2B will cause this.