Mechanism of Splicing

Mechanism of Splicing

Q. 1 Which one of the following sequence is not expressed in a mature messenger RNA of a segment of a eukaryote gene?

 A Intron

 B

Exon

 C

Plasmid

 D

TATA box

Q. 1

Which one of the following sequence is not expressed in a mature messenger RNA of a segment of a eukaryote gene?

 A

Intron

 B

Exon

 C

Plasmid

 D

TATA box

Ans. A

Explanation:

In eukaryote organisms, a structural gene usually consists of several coding regions which are known as exons that are separated by non-coding regions which are introns / intervening sequences.

They do not express.

Ref: Human Molecular Biology: An Introduction to the Molecular Basis of Health and Disease, 2003, Page 41


Q. 2

Which of the following type of RNA has splicing activity as a function:

 A

mRNA

 B

snRNA

 C

tRNA

 D

rRNA

Ans. B

Explanation:

Small Nuclear RNAs (snRNAs), a subset of the small RNAs, are significantly involved in rRNA and mRNA processing and gene regulation.

Of the several snRNAs, U1, U2, U4, U5, and U6 are involved in intron removal and the processing of mRNA precursors into mRNA.


Q. 3

What is the macromolecular complex that associates with introns during mRNA splicing?

 A

Splicer

 B

Dicer

 C

Nuclear body

 D

Spliceosome

Ans. D

Explanation:

A special multicomponent complex, the spliceosome, is involved in converting the primary transcript into mRNA. Spliceosomes consist of the primary transcript, five snRNAs (U1, U2, U4, U5, and U6) and more than 60 proteins, many of which contain conserved “RNP” and “SR” protein motifs. 

 
Ref: Weil P. (2011). Chapter 36. RNA Synthesis, Processing, & Modification. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds),Harper’s Illustrated Biochemistry, 29e.

Q. 4 Splicing Activity is a function of:

 A

mRNA

 B

sn RNA

 C

r RNA

 D

t RNA

Ans. B

Explanation:

B i.e. snRNA

–   Self splicing introns function as ribozyme and do not require external protein enzymes or high energy cofactors (eg ATP). Intron forms lariat in group II but not in group I self splicing introns.

–  Splicing is process of removing introns (i.e. the segment of gene that is not represented in mature m-RNA) from primary transcript and joining (or ligating together) exons (RNA sequences that code protein)Q. It is mediated by sn RNP or snrups formed from sn RNAQ.

Small nuclear RNAs (sn RNAs) are involved in RNA splicingQ; small nucleolar RNAs (sno RNAs) are involved in r RNA modificationsQ; micro RNAs (mi RNAs) & small temporal RNAs (st RNAs) are involved in inhibition (regulation) of gene expression (gene silencing)Q; small interfering RNAs (si RNAs) are involved in RNA interference (RNAi)Q; and B2 RNA binds to pol II and block transcription of many genes during heat shock

– Mammalian genomes seem to encode more non coding RNAs (nc RNAs) than coding m RNAs. nC RNAs are RNAS that do not encode proteins including r RNAS, t RNAs, mi RNAs, si RNAs, st RNAs and sn RNAs.


Q. 5 Some mRNA has self splicing activity. The removal of introns is/are done by:

 A Occur in intron that form Ribozyme

 B

Sp l iceosome

 C

None

 D

sn RNA

Ans. A

Explanation:

A i.e. Occurs in introns that form ribozyme


Q. 6

Defect in Snurps causes‑

 A

Sickle cell anemia

 B

Thalassemia

 C

Marfan syndrome

 D

EDS

Ans. B

Explanation:

 

Defective splicing (defect in snurps) is the most common mutation causing thalassemia.

  • Molecular defect in pathogensis of thalassemia:‑

A) β-Thalassemia

  • Most common type of genetic abnormality in β-thalassemia is point mutation i.e., nonsense.
  • Some may also occur due to deletion or insertion i.e., frame shift mutations.
  • Defect may occur at different steps of β-chain synthesis:

i) Splicing mutations

  • Mutations leading to aberrant splicing are the most common cause of P-thalassemia.

ii) Chain terminator mutations

  • This cause premature termination of mRNA translation.

iii) Promoter region mutations

  • This results in transcription defect.

B) α-Thalassemia

  • The most common cause of reduced a-chain synthesis is deletion of a-globin genes.
  • Rarely nonsense mutation may also cause a-thalassemia.


Leave a Reply

%d bloggers like this:
Malcare WordPress Security