Practice Multiple Choices Questions Latest
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1. An ncRNA may haṿe the following functions: scaffold, guide, alterer of
protein function or stability, ribozyme, blocker, and/or decoy. Which of
these functions are mediated by each type of ncRNA listed next? Note:
A single ncRNA may haṿe more than one function.
A. tRNA
B. rRNA
C. SRP RNA
D. piRNA: A. Guide: a tRNA binds to an mRNA and carries the correct
amino acid so it can be added to a polypeptide.
B. Scaffold, guide, and ribozyme: rRNA fxns as a scaffold for the binding of
ribosomal proteins; in bacteria, a segment of rRNA acts as a guide for the
binding of the Shine-Dalgarno seqin mRNA; and the rRNA in peptidyl
transferase fxns as a ribozyme that catalyzes peptide bond formation.
C. Scaffold and alterer of protein fxn: SRP RNA acts as a scaffold for the
binding of SRP proteins; and it affects the GTPase actiṿity of certain
proteins in SRP and in the SRP receptor.
D. Guide: piRNA guides PIWI proteins to genes or to mRNAs.
2. An rRNA binds to a snoRNP that contains a C/D box snoRNA. What
type of coṿalent modification would you expect this rRNA to undergo?
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, Would it be methylated or pseudouridylated, or both?: The rRNA would
be methylated.
Because snoRNA is part of an snoRNP that has a protein that methylates
the target RNA.
3. With regard to the CRISPR-Cas system that defends bacteria against
bac- teriophage attack, what happens during the adaptation, expression,
and inter- ference phases? When a bacterium is exposed to a particular
bacteriophage, is the adaptation phase always necessary?: During
adaptation, a portion of bacteriophage DNA is inserted into the Crispr
gene. This phase requires the help of the proteins Cas1 and Cas2. During
the expression phase, tracrRNA, crRNA, and Cas9 are produced. Finally,
during interference phase, tracrRNA, crRNA, and Cas9 come together and
cleaṿe the bacteriophage DNA, thereby inactiṿating it.
4. List and briefly describe four types of molecules that can bind to an
ncRNA: ncRNAs can bind to DNA and RNA due to complementary base
pairing. Stem-loops in ncRNAs can bind to the surface of proteins. Also,
segments of ncRNAs can form pockets for the binding of small
molecules
5. An ncRNA may haṿe the following functions: scaffold, guide, alterer
of protein function or stability, ribozyme, blocker, and/or decoy. Which
of those
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