This set of Cytogenetics Interview Questions and Answers for Experienced people focuses on “Initiation – 2”.
1. Which initiation factor in eukaryotes recognizes the 7-M-G cap?
Explanation: eIF4E recognized the 7-Methyl Guanine cap in the 5’ end of mRNA. This interacts with eIF4G and eIF3 which slides the 40S subunit on the mRNA looking for an initiation site.
2. Which of the following will not affect translation from the AUG involved?
a) A short hairpin near the cap
b) A hairpin 52 at downstream of cap
c) A long hairpin between cap and initiation codon
d) Providing a purine at -3 and +4 position of a start codon
Explanation: It has been seen experimentally that a hairpin 52 at further from the cap can’t help the AUG to be recognized as initiation site even when the AUG is within it. The other options here improve translation from the AUG involved.
3. IRES interact with which of the initiation factors?
Explanation: IRES is the Internal Ribosome Entry Site, this is recognized by a protein called protein X, which is further recognized by eIF4G.
4. Polysomes are ______________
a) Replication factors
c) Nuclear entity
d) Rare phenomenon
Explanation: Polysomes are the chromosomes on with a number of ribosomes are translating the same gene in a series. These tend to appear circular as that helps in recycling the ribosomes from the poly A tai to the initiation site.
5. Which poly a tail binding protein helps in the initiation of translation?
Explanation: PABP2 can bind the poly a tail to the eIF4E through the mediator eIF4G. This increases the association of the 40S subunit to the 5’ end of the mRNA thus increasing translation.
6. Which of the following is not a part of eIF4F complex?
Explanation: eIF4F is the complex that assembles at the 5’ methylated guanine cap of the mRNA to initiate translation. It has three factors eIF4A, eIF4G and eIF4E while eIF4B is not a factor of this complex.
7. Which of the following factors prevent reassociation of the 40S and 60S subunits when not bound to the mRNA?
a) eIF1 and eIF3
b) eIF2 and eIF3
c) eIF3 and eIF6
d) eIF3 and eIF4
Explanation: While he factor eIF3 binds to the 40S subunit, the other factor eIF6 binds to the 60S subunit and prevent the association of ribosomal subunits when not bound to mRNA.
8. Which one of the following has GEF activity?
Explanation: The factor eIF2B is a Guanosine nucleotide Exchange Factor or GEF. It exchanges the GDP bound to eIF2 to GTP so that it can then bind to the aminoacyl tRNA.
9. Phosphorylation of eIF4E-BP will affect translation in what way?
c) No effect
d) There is no such factor
Explanation: eIF4E-BP is the active form of the factor which can bind to the eIF4E and prevent translation. When phosphorylated, this binding is sterically prevented. Thus, phosphorylation increases translation generating free eIF4E.
10. Which of the following is done by HCR?
a) Phosphorylation of eIF4E-BP
b) Phosphorylation of eIF2-alpha
c) Dephosphorylation of eIF4E-BP
d) Dephosphorylation of eIF2-Alpha
Explanation: HCR is Heme Controlled Repressor protein which senses the lack of heme in the medium and phosphorylated eIF2-alpha. This prevents the GEF activity of eIF2B and prevents translation. This measure prevents the waste of resources.
Sanfoundry Global Education & Learning Series – Cytogenetics.
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