Ch. 11 Control of Translation

Question 1

Viruses are totally dependent on the host cell for translation of mRNA. W

Answer 1

True. Very few virus encode any translational machinery.

Question 2

What do viruses do to host cell machinery?

Answer 2

They modify it for their own benefit.

Question 3

What is the direction mRNAs are read?

What is the direction of peptide synthesis?

Answer 3

5’ to 3’; Amino to Carboxy

Question 4

What is the location of translation?

Answer 4

Ribosomes

Question 5

How long is the 5’ untranslated region?

Answer 5

3-1000 nucleotides Usually 50-70

Question 6

What causes the start and stop of translation?

Answer 6

Start and stop codons (initiation and termination)

Question 7

What follows the stop codon?

Answer 7

the 3’ Untranslated region. regulates speed of translation, stability, and initiation

Question 8

Are the majority of eukaryotic mRNA mono or poly cistronic?

Answer 8

mono. poly means there are several start and stop codons in one mRNA

Question 9

What are the components of the ribosome? What carries out their catalytic activity?

Answer 9

Small subunit (40S): 18S rRNA and 30 proteins;
Large subunit (60S): 5S, 5.8S, 28S, and 50 proteins.

The RNA

Question 10

What are the structural characteristics of tRNA

Answer 10

CCA sequence that binds amino acid; anticodon on opposite end; 70-80 nucleotides long; highly base paired L-Shape

Question 11

What are the three steps of translation? Which is rate limiting? How many proteins participate in this step?

Answer 11

Initiation, elongation, and termination.
Initiation is rate limiting
At least 11

Question 12

What three proteins promote dissociation of ribosome in order to start initiation?

Answer 12

ElF1A, elF3, and elF6

Question 13

What is the role of secondary structure in the 5’ UTR?

Answer 13

a stable 2ndary structure in 5’ region inhibits translation by blocking ribosome movement

Question 14

What does elF4A do?

Answer 14

It has RNA helicase activity that helps in unwinding of dsRNA near the 5’ end. (helps eliminate 2ndary structure)

Question 15

What is the start codon?

Answer 15

Aug (for over 90% of mRNA)

Question 16

A purine at the -3 position does what?

Answer 16

It allows start codon to be recognized most efficiently.

Question 17

What is the role of ElF1?

Answer 17

It selects the initiation codon

Question 18

What are the other start codons for viral mRNA? Why does this work?

Answer 18

ACG, GUG, and CUG;

Parts of viral mRNA mimic tRNA to occupy P site and allow initiation to take place at A site

Question 19

What is one way that virus prevents cellular mRNA translation?

Answer 19

Cleavage of ElF4G with a protease which prevents cellular initiation complex from forming, since the cleaved protein can only translate at the IRES (internal ribosome entry site) Poliovirus

Question 20

What is ribosome shunting?

Answer 20

When the ribosome bypasses secondary structure in 5’ UTR

Question 21

What does Reinitiation do?

Answer 21

It produces 2 proteins from a single mRNA

Question 22

What is ribosomal frameshifting?

Answer 22

The ribosome moves back or forward one nucleotide, which is present in viral and cellular systems

Question 23

To what extent can a virus take over the host machinery?

Answer 23

The virus can completely change synthesis towards viral proteins.

Question 24

What are cellular defenses?

Answer 24

Release of interferon leads to an antiviral state;
RNA activated protein kinase (Pkr) are produced, which phosphorylates elF2alpha and inhibits translation. Can happen in presence of dsRNA

Question 25

What are some viral defenses against Pkr?

Answer 25

Adenoviral protein VA-RNA I inhibits Pkr;
Vaccinia virus E3L sequesters dsRNA;
some proteins act as a pseudosubstrate;
in HSV1, ICP 34.5 dephosphorylates elF2alpha