Biology

DNA and Genetics

1,095 Questions

DNA and genetics questions explore molecular biology, DNA replication, and genetic engineering techniques. These topics are essential for various competitive exams requiring a strong foundation in life sciences. Practice these questions to understand complex biological processes thoroughly.

DNA replication mechanismsGenetic engineering techniquesGene editing toolsPolymerase chain reactionDNA sequencing methods

DNA and Genetics Questions

Multiple choice expression of gene inherited changes biology

Prokaryotic enzyme with 5'--> 3 exonuclease property is

  1. DNA polymerase I

  2. DNA polymerase II

  3. DNA polymerase III

  4. Both A and C
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

DNA polymerase I is unique among the prokaryotic DNA polymerases because it possesses 5' to 3' exonuclease activity, which is essential for removing RNA primers during DNA replication.

Multiple choice expression of gene inherited changes biology

Which of the following DNA polymerase of prokarytoes have both 3' - 5' and 5' - 3' exonuclease activity

  1. DNA Pol-II

  2. DNA Pol-I

  3. DNA Pol-IV

  4. DNA Pol-III
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

DNA polymerase I is the only prokaryotic DNA polymerase that possesses both 3' to 5' exonuclease activity (for proofreading) and 5' to 3' exonuclease activity (for primer removal).

Multiple choice expression of gene inherited changes biology

In Negative operon : -

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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'.
Multiple choice expression of gene inherited changes biology

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

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice expression of gene inherited changes biology

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.

  1. $2$
  2. $3$
  3. $4$
  4. $5$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Statements A, C, and D are generally considered correct in biological contexts. Statement B is incorrect because the lac operon is under positive regulation by CAP (Catabolite Activator Protein), not negative regulation. Thus, 3 statements are correct.

Multiple choice expression of gene inherited changes biology

Regulator gene controls chemical synthesis(Operon concept) by.

  1. Inhibiting transcription

  2. Inhibiting enzymes

  3. Inhibiting passage of mRNA

  4. Inhibiting substrate enzyme reaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The regulator gene produces a repressor protein that binds to the operator, thereby inhibiting the transcription of the structural genes into mRNA.

Multiple choice expression of gene inherited changes biology

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?

  1. Three

  2. Four

  3. One

  4. Two
Reveal answer Fill a bubble to check yourself
D Correct answer
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'. 
Multiple choice expression of gene inherited changes biology

Which one of the following is wrong:

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice expression of gene inherited changes biology

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?

  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.
Reveal answer Fill a bubble to check yourself
D Correct answer
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.'.

Multiple choice expression of gene inherited changes biology

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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'.

Multiple choice expression of gene inherited changes biology

In an operon model, regulator gene function as

  1. Repressor

  2. Regulator

  3. Inhibitor

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

Multiple choice expression of gene inherited changes biology

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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'.

Multiple choice expression of gene inherited changes biology

Inducible operons differ from repressible operons in that

  1. operator of inducible operons is switched off by a repressor protein

  2. inducible operons have an operator that controls binding of RNA polymerase to the promoter region

  3. inducible operons use activators and positive control to regulate their transcription

  4. inducible operons usually include structural genes that function in catabolic pathways
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The inducible operon is usually off and it can be induced in the presence of inducer like lactose. After getting induced, the operon is turned on and transcription takes place to catabolize these inducers. Hence, the inducible operon is usually involved in catabolism. 

While repressible operon is on normally and results in transcription of structural genes to produce the desired product for e.g. tryptophan. Hence, it works at times when the bacterial cell does not require these products like tryptophan and the presence of tryptophan from external source turns off this operon. 
So, the correct option is 'inducible operons usually include structural genes that function in catabolic pathways'.

Multiple choice expression of gene inherited changes biology

Choose the correct answer from the alternatives given :
Repressible operon system is usually found in (i) pathways. The pathways end product serves as a (ii) to activate the repressor, turn off enzyme synthesis and prevent overproduction of the end product of the pathway. Genes for this operon are usually switched (iii) and the repressor is synthesised in an (iv) form.

  1. (i) anabolic, (ii) corepressor, (iii) on, (iv) - inactive

  2. (i) anabolic, (ii) inducer, (iii) off, (iv) - active

  3. (i) catabolic, (ii) inducer, (iii) off, (iv) - active

  4. (i) catabolic, (ii) corepressor, (iii) on, (iv) - inactive
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Repressible operons are generally involved in anabolic pathways, or the synthesis of an essential component, while inducible operons are generally involved in catabolic pathways or the breakdown of a nutrient. Positive control of an operon is when gene expression is stimulated by the presence of a regulatory protein. The repressible operon work on the feedback inhibition mechanism which is the phenomenon where the output of a process is used as an input to control the behavior of the process itself and the co-repressor serves as to activate the repressor. Genes of a repressible operon are switched off as they are required to synthesize the structural/functional genes in the absence of the repressor. The presence of the repressor can stop this process and hence the repressor is present in the inactive form. 

So, the correct option is '(i) anabolic, (ii) corepressor, (iii) on, (iv) - inactive'.