Biology

DNA and Genetics

985 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 dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

Choose the correct answer from the alternatives given :
The enzyme DNA dependent RNA polymerase catalyses the polymerisation reaction in ________ direction.

  1. Only 5 $\rightarrow$ 3
  2. Only 3 $\rightarrow$ 5

  3. Both (a) and (b)

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The two strands have opposite polarity and the DNA-dependent RNA polymerase also catalyze the polymerization in only one direction, that is, 5 →→ 3, the strand that has the polarity 3 →→ 5 acts as a template, and is also referred to as template strand. The other strand which has the polarity 5 →→ 3 and the sequence same as RNA (except thymine at the place of uracil) is displaced during transcription. This strand (which does not code for anything) is referred to as coding strand.

So, the correct answer is 'Only 5 → 3'.

Multiple choice dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

Choose the correct answer from the alternatives given :
Other than DNA polymerase, which are the enzymes involved in DNA synthesis?

  1. Topoisomerase

  2. Helicase

  3. RNA primase

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Process of DNA synthesis whereby a parent DNA molecule is faithfully copied, giving rise to two identical daughter molecules is called DNA replication. In DNA synthesis, DNA polymerase plays an important role having the capability to elongate an existing DNA strand but cannot initiate the synthesis. So, the synthesis is initiated with the help of RNA primer formed by RNA primase RNA primase synthesises the short RNA primer of about 10 nucleotides that is elongated by DNA polymerase to form an Okazaki fragment of DNA during DNA replication. Helicase unzips the two strands of DNA and topoisomerase reduces the coiling tension developed due to the unwinding of the two strands.

So the correct answer is 'All of these'.

Multiple choice expression of gene inherited changes biology

In E.coli _________________________ genes are grouped in  _______________ operon.

  1. $64,20$
  2. $3,100$
  3. $34,10$
  4. $260,75$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In E.coli, a single circular, nacked dsDNA molecule act as a genetic material. It contains 64 genes and are grouped into 20 operons.

So, the correct option is ’64, 20’.

Multiple choice expression of gene inherited changes biology

Functioning of structural genes is controlled by

  1. Operator

  2. Ligase

  3. Regulator gene

  4. Polymerase
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Operon can be defined as DNA segment having a cluster of genes which are controlled by single promoter. It consists of operator gene and structural genes. The operator gene regulates the expression of structural genes by providing a binding site to transcription factor which in turn regulate the gene expression by altering the binding of RNA polymerase to the promoter region. A promoter is a DNA segment where transcription of a particular gene starts. The regulator genes code for transcription factor/repressor proteins that binds to operators or promoters and prevent RNA polymerase from transcribing RNA. The alteration in repressor proteins by inducers make them unable to bind DNA and allow RNA polymerase to carry out transcription. Thus regulator gene control the functioning of structural genes via operator gene. Option C is correct answer.

Multiple choice expression of gene inherited changes biology

Functioning of structural genes is controlled by

  1. Operator

  2. Promoter

  3. Ligase

  4. Regulator gene
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Operon can be defined as DNA segment having a cluster of genes which are controlled by single promoter. It consists of operator gene and structural genes. The operator gene regulates the expression of structural genes by providing a binding site to transcription factor which in turn regulate the gene expression by altering the binding of RNA polymerase to the promoter region. A promoter is a DNA segment where transcription of a particular gene starts. Ligase enzymes facilitate the joining of two DNA strand together by phosphodiester bonds. The regulator genes code for transcription factor/repressor proteins that binds to operators or promoters and prevent RNA polymerase from transcribing RNA. The alteration in repressor proteins by inducers make them unable to bind DNA and allow RNA polymerase to carry out transcription. Thus regulator gene control the functioning of structural genes via operator gene. Option D is correct answer.

Multiple choice expression of gene inherited changes biology

A co-ordinated unit which controls the genetic expression is called as a/an

  1. Cistron

  2. Recon

  3. Operon

  4. Muton
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Cistron: Is a section of a DNA or RNA molecule that codes for a specific polypeptide in a protein synthesis.
Recon: In a cistron, the recombinational units may be more than one. Thus, the smallest unit capable of undergoing recombination is called as a recon.
Muton: It may be defined as, "the smallest unit of DNA which may be changed is the nucleotide''. Therefore, cistron is the largest unit in size followed by recon and muton. This can be explained that a gene consists of several cistron, a cistron contains many recons and a recon contains a number of mutons. 
Operon: It is a unit of genetic material that functions in a co-ordinated manner by means of an operator, a promoter and one or more structural genes that are transcribed together.
Thus, the correct answer is option C.
Multiple choice expression of gene inherited changes biology

Operon contains

  1. Operator and regulator genes

  2. Operator and structural genes

  3. Operator, regulator genes and repressor

  4. Operator gene, regulator gene, repressor gene, structural genes and promoter gene
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

  • Operator gene is a segment of DNA present between the promoter and the genes of the operon. It helps in transcribing the genes of the operon.
  • Regulator gene often codes for repressor proteins which bind with the operator and checks the operon.
  • Repressor gene physically obstructs the RNA polymerase from transcribing the genes by binding with the operator gene.
  • Structural genes are the genes that undergo translation to produce enzymes and are co-regulated by the operon.
  • Promoter gene is a nucleotide sequence that enables a gene to be transcribed. It is recognized by RNA polymerase, which then initiates transcription.
So, the correct option is 'Operator gene, regulator gene, repressor gene, structural genes and promoter gene'.

Multiple choice expression of gene inherited changes biology

Which of the following is an example of positive gene regulation?

  1. The tryptophan gene, in which the presence of tryptophan functions as a corepressor to prevent its own transcription.

  2. The lac gene, in which the repressor preventing the synthesis of the enzymes that degrade lactose is deactivated by the presence of lactose.

  3. CAP, which acts as a required transcription factor for the enzymes that degrade lactose.

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

Regulation of functioning of the expression of genes is known as the regulation of gene expression. It is basically of three types- inducible, constitutive and repressible.

The repressible kind of control is when the product of regulatory gene initiates the expression of the gene under its control.
The tryptophan consists of repressible Operon model in which when the end product tryptophan is present in sufficient amount it's molecules act as corepressor and the structural genes become switched this is also known as feedback repression or positive regulation.

So, the correct option is 'The tryptophan gene, in which the presence of tryptophan functions as a corepressor to prevent its own transcription.'

Multiple choice expression of gene inherited changes biology

Genes that are involved in turning on or off the transcription of a set of structural genes are called as

  1. Polymorphic genes

  2. Operator genes

  3. Redundant genes

  4. Regulatory genes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Regulator gene regulates the expression of structural genes by its protein products that are mostly transcription factors. These transcription factors bind to the operator region which is located just upstream the binding site of the RNA polymerase and hence prevent the binding and transcription; option D is correct. Operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as repressor protein binding site; option B is wrong. Genes which govern more or less same trait or perform same role are called redundant genes; presence of these genes confers advantage of diluting the effect of point mutation on organisms; option C is wrong. Presence of more than one allele on a genetic locus is called gene polymorphism provided that the allele is present with more than 5% frequency in the population; option A is wrong. 

Multiple choice expression of gene inherited changes biology

According to the operon concept, the regulatory gene regulates the chemical reactions of the cell by

  1. Inactivating enzymes in the reaction

  2. Inhibiting transcription of mRNA

  3. Inhibiting migration of mRNA into cytoplasm

  4. Inhibiting the substrate in the reaction
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

An operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create monocistronic mRNAs that are translated separately. Regulator gene regulates inhibiting transcription of mRNA.

Multiple choice expression of gene inherited changes biology

Regulated unit of genetic material is termed as

  1. Operon

  2. Regulator gene

  3. Operator gene

  4. Okazaki segment
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An operon is a cluster of genes under the control of a single promoter, functioning as a regulated unit of genetic material in prokaryotes.

Multiple choice expression of gene inherited changes biology

Tryptophan operon of Escherichia coli is

  1. Monocistronic

  2. Inducible

  3. Unregulated

  4. Repressible
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The tryptophan operon is a repressible operon, meaning it is normally active and is turned off when the end product (tryptophan) is present in sufficient quantities.

Multiple choice expression of gene inherited changes biology

Part of operon producing repressor is known as

  1. Repressor gene

  2. Operator gene

  3. Regulator gene

  4. Promoter gene
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The regulator gene (or regulatory gene) is the part of the operon system that codes for the repressor protein.

Multiple choice expression of gene inherited changes biology

Genes that are involved in turning on or turning off the transcription of a set of structural genes are called as

  1. Polymorphic genes

  2. Operator genes

  3. Redundant genes

  4. Regulatory genes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the operon model, the operator is the gene segment to which a repressor binds. This prevents the RNA polymerase from transcribing certain genes in the operon unit.

Multiple choice expression of gene inherited changes biology

In lac operon model, repressor protein binds to which site?

  1. Structural genes

  2. Promotor

  3. Operator

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Lac repressor is part of the regulatory network of the lac operon. Lac repressor controls the production of three proteins produced from the gene and affecting the metabolism of lactose. This repressor molecule is a tetramer whose all the subunits are identical. This tetramer binds to a particular region in the bacterial DNA called the operator. This region is present next the three lactose metabolizing proteins. Binding of the repressor to operator causes the block in the production of protein. Otherwise, for three genes to transcribe the repressor protein binds to the lactose molecule and hence unable to bind to operator allows the genes to transcribe.