Tag: biology

Questions Related to biology

In Negative operon : -

expression of gene inherited changes biology

  1. Inducer binds with repressor

  2. Co-repressor does not binds with repressor

  3. Corepressor binds with inducer

  4. CAMP have negative effect on lac operon

Show answer
Correct Option: A
Explanation:
The inducer is a molecule that regulates gene expression. An inducer can bind to protein repressors or activators. The lac operon is a negatively controlled inducible operon, where the inducer molecule is Lactose. If the inducer molecule is present, it binds to the repressor and changes its conformation so that it is unable to bind to the operator and thus gene expression is controlled.
So, the correct answer is 'Inducer binds with repressor'.

The function of a repressor protein in an operon system is to prevent protein synthesis by binding to ________________.

expression of gene inherited changes biology

  1. The ribosome

  2. The RNA polymerase, thus blocking transcription

  3. A specify region of the mRNA, preventing translation to protein

  4. A specific region of the operon, preventing transcription of structural genes

Show answer
Correct Option: A

How many of the following statements are correct
(A) In prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression
(B) Lac operon is under negative regulation of CAP.
(C) Presence of intron is reminiscent of antiquity.
(D) Inheritance of a character is also affected by promoter and regulatory sequence of a structural gene.

expression of gene inherited changes biology

  1. $2$

  2. $3$

  3. $4$

  4. $5$

Show answer
Correct Option: B

Regulator gene controls chemical synthesis(Operon concept) by.

expression of gene inherited changes biology

  1. Inhibiting transcription

  2. Inhibiting enzymes

  3. Inhibiting passage of mRNA

  4. Inhibiting substrate enzyme reaction

Show answer
Correct Option: A

Read the following four statements (A-D) :
(A) In transcription, adenine pairs with uracil.
(B) Regulation of lac operon by repressor is referred to as positive regulation.
(C) The human genome has approximately 50,000 genes.
(D) Haemophilia is a sex-linked recessive disease.
How many of the above statements are correct?

expression of gene inherited changes biology

  1. Three

  2. Four

  3. One

  4. Two

Show answer
Correct Option: D
Explanation:
A. Transcription is the process of synthesis of RNA from a template DNA by the replicative enzyme RNA polymerase. As we know, purine bases pair with pyrimidine bases i.e. Adenine pairs with Thymine or vice versa and Guanosine pairs with Cytosine or vice versa. Since RNA has Uracil instead of Thymine, Adenine pairs with Uracil in transcription. Hence, statement A is correct.
B. The regulation of lac operon by repressor is negative regulation as in the presence of repressor (lactose in case of E. coli), the transcription of the structural gene doesn't occur because repressor binds to the operator region and due to this, RNA polymerase can't proceed transcription. Hence, statement B is incorrect.
C. Human genome has approximately 30,000-40,000 genes. Hence, statement C is incorrect. 
D. Haemophilia is a sex linked disorder. It is a X-linked recessive disease which is caused by a recessive gene located on X chromosome. Hence, statement D is correct.
So, out of all statements given in the question, statements A and D are correct.
So, the correct answer is 'Two'. 

Which one of the following is wrong:

expression of gene inherited changes biology

  1. $Y$ in Lac Operon is responsible for $\beta$ galactoside permease

  2. In Lac-operon the repressor becomes inactive if it binds with lactose

  3. In repressible control of gene action the repressor cannot bind to promotor if co repressor is present

  4. Tryptophan operon consists of five structural genes

  5. The mRNA produced from a bacterium is usually polycistronic

Show answer
Correct Option: A

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'.