Molecular Basis of Inheritance — Page 4 | NEET Biology

Q31

In an inducible operon, the genes are

A Always expressed

B Usually not expressed unless a signal turns them on

C Usually expressed unless a signal turns them off

D Never expressed

Correct Answer

Option B

Solution

(b) Inducible operons are normally switched off; an inducer turns them on.

Q32

Which enzymes will be produced in a cell in which there is a nonsense mutation in the lac Y gene?

A Lactose permease

B Transacetylase

C Lactose permease and transacetylase

D beta-galactosidase

Correct Answer

Option D

Solution

(d) If y gene has nonsense mutation only z gene product (beta-galactosidase) is still produced.

Q33

In eukaryotes, after transcription of mRNA, some nucleotides are removed before translation. These nucleotides are called

A exons

B upstream sequences

C unusual bases

D introns

Correct Answer

Option D

Solution

(d) Introns (non-coding sequences) are removed by splicing before mRNA is translated.

Q34

During development of an organism, the product of one gene is required to activate another gene. Such gene products are called

A transcription factors

B episomes

C coenzymes

D catalase

Correct Answer

Option A

Solution

(a) Transcription factors regulate gene expression during development.

Q35

Reverse transcriptase is

A RNA dependent RNA polymerase

B DNA dependent RNA polymerase

C DNA dependent DNA polymerase

D RNA dependent DNA polymerase

Correct Answer

Option D

Solution

(d) Reverse transcriptase synthesises DNA using RNA as template (RNA-dependent DNA polymerase).

Q36

Protein helping in opening of DNA double helix in the form of replication fork is

A DNA gyrase

B DNA polymerase I

C DNA ligase

D DNA topoisomerase

Correct Answer

Option A

Solution

(a) DNA gyrase helps relieve supercoiling ahead of the replication fork.

Q37

In split genes, the coding sequences are called

A introns

B operons

C exons

D cistrons

Correct Answer

Option C

Solution

(c) Exons are coding sequences that are retained in mature mRNA.

Q38

The translation termination triplet is

A UAU

B UAA

C UAC

D UGC.

Correct Answer

Option B

Solution

(b) UAA (ochre), UAG (amber) and UGA (opal) are stop codons.

Q39

Okazaki fragments are seen during

A transcription

B translation

C replication

D transduction

Correct Answer

Option C

Solution

(c) Okazaki fragments are discontinuous segments synthesised on the lagging strand during DNA replication.

Q40

Binding of specific protein on regulatory DNA sequence can be studied by means of

A ultra centrifugation

B electron microscope

C light microscope

D X-ray crystallography

Correct Answer

Option D

Solution

(d) X-ray crystallography reveals protein-DNA interactions at atomic resolution.