This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Gene Expression Control – Translational Control”.
1. Which of the following are untranslated regions of messenger RNAs?
Explanation: The untranslated regions of messenger RNAs are called untranslated regions. These regions do not code for proteins but play a vital role in translational-level control.
2. Which of the following is not an aspect of translational-level control?
a) mRNA degradation
b) mRNA localization
c) mRNA translation
d) mRNA stability
Explanation: There are three distinct aspects of translational-level control in eukaryotic gene expression; mRNA localization, mRNA translation and mRNA stability. The translational-level control takes place in cytoplasm.
3. Messenger RNA from which gene is localized at the anterior end of fruit fly?
Explanation: During oogenesis, messenger RNA transcribed from the bicoid gene of fruit fly is specifically localized at the anterior end of the oocyte while mRNA from the oskar gene becomes localized at the opposite end.
4. During the process of cytoplasmic localization, translation is inhibited.
Explanation: During the period of cytoplasmic localization, proteins associate with the messenger RNA in the cytoplasm. Translation of the mRNA is specifically inhibited and the control of translation takes place.
5. Pre-synthesized mRNAs are stored in the __________________ in an inactive state.
c) nuclear membrane
d) plasma membrane
Explanation: Pre-synthesized mRNAs are stored in the cytoplasm in an inactive state for future translation. When translation of these stored mRNA takes place, the inhibitory proteins are removed and poly-adenine tail is lengthened.
6. When human cell is subjected to stressful condition ___________________ is activated.
a) protein kinase
Explanation: When a human cell is subjected to stressful conditions, protein kinase is activated whose main function is to phosphorylate the ignition factor eIF2, thereby blocking further protein synthesis.
7. Which of the following is a contributor of mRNA stability?
b) Poly(A) tail
Explanation: The mRNA undergoes post transcriptional modification to prevent premature degradation in the cytoplasm. The mRNA undergoes 5’ capping by a methylated guanosine residue and a 3’ Poly-A-tail using the Rho protein.
8. The degradation of mRNA begins, when its tail reduces to _________ residues.
Explanation: When an mRNA leaves the nucleus, it contains roughly 200 adenine residues (in the poly-adenine tail), but these are nibbled away by a deadenylase. The degradation of mRNA starts when the residues are reduced to 30.
9. Which of the following is a temporary storage site for RNAs?
Explanation: Cytosolic mRNA with a high rate of formation(such as housekeeping genes) form P-bodies which is the site of mRNA degradation and temporary storage.
10. To carry out translational-level control, miRNAs bind to __________ of their target mRNAs.
c) intergenic sites
d) exonuclease sites
Explanation: To carry out translational-level control, the micro RNAs bind to the 3’ (3-prime) UTRs i.e. un-translated regions of the target messenger RNA molecules.
11. Which enzyme is responsible for the synthesis of microRNAs?
Explanation: Dicer is the enzyme that brings about the synthesis of microRNAs. Since miRNAs play an important role in translational-level control, absence of dicer influences the growth and development of a specific compound.
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