Tag: inherited changes

Questions Related to inherited changes

Choose the correct answer from the alternatives given :
You have created a fusion between trp operon and lac operon which encodes the enzymes for tryptophan biosynthesis, under the regulatory control of the lac operator. Under which of the following conditions will tryptophan synthase be induced in the strain that carries the chimeric operator fused operons?

expression of gene inherited changes biology

  1. Only when both lactose and glucose are absent.

  2. Only when both lactose and glucose are present.

  3. Only when lactose is absent and glucose is present.

  4. Only when lactose is present and glucose is absent.

Show answer
Correct Option: D
Explanation:

As the chimeric operon is under control of operator gene of lac operon, it will be functional only in the conditions required for lac operon to be functional. In lac operon lactose function as inducer hence its presence in medium is essential for proper functioning while glucose inhibits its function. So, the chimeric operon will produce tryptophan only when lactose is present and glucose is absent in the medium.

So, the correct answer is 'Only when lactose is present and glucose is absent.'.

Choose the correct answer from the alternatives given.
An operon is a

expression of gene inherited changes biology

  1. Protein that suppresses gene expression

  2. Protein that accelerates gene expression

  3. Cluster of structural genes with related functions

  4. Gene that switches other genes on or off

Show answer
Correct Option: C
Explanation:

An operon, in genetics, is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The promoters are the palindromic sequences that control the process of transcription. An operon can be inducible like lac operon or it can be inhibitor operon like trp operon. 

So, the correct option is 'Cluster of structural genes with related functions'.

Choose the correct answers from the alternatives given.
The prokaryotic genetic system contains:       

expression of gene inherited changes biology

  1. either DNA or histones

  2. neither DNA nor histones

  3. DNA and histones

  4. DNA but no histones

Show answer
Correct Option: D
Explanation:

The prokaryotic genetic system does not have a nucleus in their cell but the genome in a prokaryote is held within a DNA in the cytosol called nucleoid.

Eukaryotes have DNA wrapped around the histones but prokaryotes do not contain histones.
Hence, the correct answer is, 'DNA but no histones'.

In Prokaryotes, the predominant site for control of gene expression is 

expression of gene inherited changes biology

  1. Transcriptional intimation

  2. Processing level

  3. Transfer of mRNA from nucleus to the cytoplasm

  4. Translation initiation

Show answer
Correct Option: A
Explanation:
Regulation of gene expression refers to a very broad term that may occur at various levels. In prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression. 
Considering that gene expression results in the formation of a polypeptide, it can be regulated at several levels. In eukaryotes, the regulation could be exerted at
(i) transcriptional level (formation of primary transcript),
(ii) processing level (regulation of splicing),
(iii) transport of mRNA from the nucleus to the cytoplasm,
(iv) translational level.

So, the correct option is 'Transcriptional intimation'.

Choose the correct answer from the alternatives given :
Control of gene expression takes place at the level of

expression of gene inherited changes biology

  1. DNA-replication

  2. Transcription

  3. Translation

  4. None of the above.

Show answer
Correct Option: B,C
Explanation:

Regulation of gene expression refers to a very broad term that may occur at various levels. In eukaryotes the gene expression can be regulated at transcriptional level, processing level, transport of mRNA from nucleus to the cytoplasm, and translational level whereas in prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression.

So, the correct answer is 'Transcription and Translation'.

In an operon model, regulator gene function as

expression of gene inherited changes biology

  1. Repressor

  2. Regulator

  3. Inhibitor

  4. All of the above

Show answer
Correct Option: D
Explanation:

Operon model contains a cluster of genes which are under the control of single promoter. It consists of an operator, promoter, regulator and structural genes. The regulator gene function as a repressor as it produces repressor protein that binds to the operator and thus inhibits the transcription of the structural genes. It functions as regulator as it regulates the transcription of structural gene. The product of regulator gene is inhibitor that keeps the operon model turned off.

Thus, the correct answer is option D.

Match the columns and find out correct combination.

Gene Product Function of the product
I. Z-gene $\beta$-galactosidase Hydrolysis of lactose
II. y-gene Transacetylase Uptake of lactose
III. a-gene Permease protien Function not-known
IV. Inhibitor gene Repressor protien Switch off operator gene
expression of gene inherited changes biology

  1. II and III

  2. I and III

  3. I, III, IV

  4. I and IV

Show answer
Correct Option: D
Explanation:

I. The z gene that codes for the enzyme beta-galactosidase that hydrolyzes lactose to glucose and galactose.

IV. Inhibitor is a represser protein which switch off the process in lac operon process. 

Morphogensis is controlled by______________ 

expression of gene inherited changes biology

  1. Gibberellins and Cytokinin

  2. Auxin and Cytokinin

  3. Auxin and Gibberellins

  4. Gibberellins and Zeatin

Show answer
Correct Option: A
Explanation:

Morphogenesis is a process that controls the organized spatial distribution of cells during embryonic development. It can also take place in a matured organism in cell culture or in tumor cell masses. It is concerned with the shape of tissues. Plant growth regulators such as gibberellins, cytokinins, abscisic acid and ethylene control growth and development in plants. Gibberellins and cytokinins are the two instrumental hormones that play a key role in morphogenesis. Whereas auxins stimulate the plant cell to grow long.

So the correct answer is 'gibberellin and cytokinin'.

When Tryptophan is present

expression of gene inherited changes biology

  1. repressor is unable to bind to the operator

  2. transcription of structural genes occurs

  3. repressor is able to bind to the operator

  4. both (a) and (b)

Show answer
Correct Option: C
Explanation:

The Trp operon is an example of a repressible operon; it is on unless turned off by a repressor protein. The repressor protein is synthesized by trpR. While the repressor protein is always present in the cell, it is synthesized in an inactive form. When a corepressor is present, in this case, tryptophan, it binds to the repressor protein in an allosteric site. This changes the conformation of the protein such that it can bind to the operator and block transcription by preventing the binding of RNA polymerase to the promoter. In this way, the cell saves energy by not producing tryptophan when it is already present.

So, the correct option is 'repressor is able to bind to the operator'.

A mutation that renders the regulatory gene of a repressible operon nonfunctional would result in

expression of gene inherited changes biology

  1. excessive synthesis of a catabolic activator protein

  2. irreversible binding of the repressor to the promoter

  3. inhibition of transcription of the structural genes

  4. continuous transcription of the structural genes

Show answer
Correct Option: D
Explanation:

In a repressible operon, the operon is normally on and transcription occurs for the synthesis of enzymes. This synthesis of enzymes takes place with the help of the structural genes.

In presence of corepressor (for e.g. tryptophan in trp operon) inactive repressor (aporepressor) gets converted to the active repressor. This active repressor binds to operator region and stops transcription. If any mutation takes place in regulatory genes i.e. those involved in the formation of operator and repressor, operon will never get turned off. This will result in continuous transcription of the structural genes. 
So, the correct option is 'continuous transcription of the structural genes'.