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Molecular Basis of Inheritance

NEET Biology · 262 questions · Page 15 of 27 · Click an option or "Show Solution" to reveal answer

Q141
In Escherichia coli, lac operon is induced by
A lactose
B promoter gene
C β\beta-galactosidase
D I-gene
Correct Answer
Option A
Solution

(a) Lac operon is an inducible operon system.

Which remains switched off normally but becomes operational in the presence of inducer lactose.

Q142
The lac operon is an example of
A arabinose operon
B inducible operon
C repressible operon
D overlapping genes
Correct Answer
Option B
Solution

(b) The lac operon consists of a promotor gene, an operator gene and structural genes.

There are three structural genes designated as z,yz, y and a, which code for the enzymes beta-galactosidase, lac permease and transacetylase respectively.

It is an example of inducible operon.

Q143
An environmental agent, which triggers transcription from an operon, is a
A regulator
B inducer
C depressor
D controlling element
Correct Answer
Option B
Solution

(b) The inducer is an environmental agent, which triggers transcription from an operon.

The inducer or effector molecule are small sized which can bind to a regular protein.

Q144
The wild type EE. coli cells are growing in normal medium with glucose. They are transferred to a medium containing only lactose as sugar. Which of the following changes takes place?
A The lac operon is repressed
B All operons are induced
C The lac operon is induced
D E.coli cells stop dividing
Correct Answer
Option C
Solution

(c) If Escherichia coli bacteria grow in normal glucose medium and when transferred to a medium containing lactose, then the lac operon is induced.

Q145
The RNA that picks up specific amino acids from the amino acid pool in the cytoplasm to ribosome during protein synthesis is called
A mRNA
B tRNA
C rRNA
D carrier RNA
Correct Answer
Option B
Solution

(b) mRNA or messenger RNA brings coded information from DNA to form polypeptides. rRNA or ribosomal RNA occurs inside ribosomes and is involved in protein synthesis.

Q146
In operon concept, regulator gene functions as a repressor
A repressor
B regulator
C inhibitor
D all of these
Correct Answer
Option A
Solution

(a) Regulator gene produces a biochemical for suppressing the activity of the structural gene.

Q147
In sea urchin DNA, which is double stranded, 17% of the bases were shown to be cytosine. The percentages of the other three bases expected to be present in this DNA are:
A G 17%, A 16.5%, T 32.5%
B G 17%, A 33%, T 33%
C G 8.5%, A 50%, T 24.5%
D G 34%, A 24.5%, T 24.5%
Correct Answer
Option B
Solution

(b) Chargaff rule states that A=T and G=C. If C is 17%, then G is 17%, A is 33%, T is 33%.

Q148
A complex of ribosomes attached to a single strand of RNA is known as
A Polysome
B Polymer
C Polypeptide
D Okazaki fragment
Correct Answer
Option A
Solution

(a) A polysome or polyribosome is a complex of an mRNA molecule and two or more ribosomes, which is formed during the active translation process.

Q149
The association of histone H1 with a nucleosome indicates:
A DNA replication is occurring.
B The DNA is condensed into a Chromatin Fibre.
C The DNA double helix is exposed.
D Transcription is occurring.
Correct Answer
Option B
Solution

(b) The association of H1 protein indicates the complete formation of nucleosome which requires DNA condensation.

The DNA is therefore in condensed form.

Q150
Which of the following RNAs should be most abundant in animal cell?
A t-RNA
B m-RNA
C mi-RNA
D r-RNA
Correct Answer
Option D
Solution

(d) Ribosomal RNA (rRNA) is most abundant in animal cell. It constitutes 80%80\% of total RNA of the cell.

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