Biology

Molecular Genetics

851 Questions

Molecular genetics explores the mechanisms of genetic information transfer, including DNA replication, transcription, and translation. It is a core component of biology syllabi. These concepts frequently appear in general science sections of major competitive exams.

DNA replicationTranscription processTranslation processRNA typesCentral dogma

Molecular Genetics Questions

Multiple choice bio-chemistry nucleic acids central dogma transcription and gene expression molecular biology

In reverse transcription.......... is assembled on ..........

  1. mRNA, DNA

  2. DNA, agar

  3. cDNA, mRNA

  4. DNA, enzymes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Complementary DNA is DNA synthesized from a single-stranded mRNA template in a reaction catalyzed by the enzyme reverse transcriptase. This process is known as reverse transcription. cDNA is often used to clone eukaryotic genes in prokaryotes. Hence it can be said that in reverse transcription cDNA is assembled on mRNA. 

So, the correct option is 'cDNA, mRNA'.

Multiple choice bio-chemistry nucleic acids central dogma transcription and gene expression molecular biology

All RNA except .......... is made from DNA.

  1. tRNA

  2. mRNA

  3. rRNA

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

cDNA or complementary DNA is the DNA synthesized from a single-stranded RNA template in a reaction catalysed by reverse transcriptase enzyme. This cDNA is naturally produced by retroviruses where RNA acts as the genetic material. It is also used to clone eukaryotic genes in prokaryotes.

Remaining tRNA, mRNA and rRNA are synthesised from DNA through the process of transcription using RNA polymerase enzyme.
So, the correct option is 'cDNA'.

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

During splicing, the exons are joined and the enzyme which catalyzes this reaction is 

  1. RNA ligase

  2. RNA catalase

  3. RNA polymerase

  4. RNA primase
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
RNA primase synthesizes RNA primer which is a strand segment (complementary to the template) and has a free 3’ hydroxyl group to facilitate addition of nucleotides by polymerase enzymes. RNA polymerase synthesizes RNA using DNA template strand by adding the ribonucleotides to a primer in 5' to 3' direction via phosphodiester bonds. Splicing is removal of introns from the primary transcript and ligation of exons to form a continuous sequence specifying a functional polypeptide. RNA ligase enzyme joins two exons together via phosphodiester bond between 3’ hydroxyl at the end of one exon and a 5’ phosphate at the end of another exon. 
Multiple choice dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

Exon segments are reunited after splicing by

  1. RNA primase

  2. DNA polymerase

  3. RNA polymerase

  4. RNA ligase
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
RNA primase synthesizes RNA primer which is a stranded segment (complementary to the template) and has a free 3’ hydroxyl group to facilitate the addition of nucleotides by polymerase enzymes. RNA polymerase synthesizes RNA using DNA template strand by adding the ribonucleotides to a primer in 5' to 3' direction via phosphodiester bonds. Splicing is the removal of introns from the primary transcript and ligation of exons to form a continuous sequence specifying a functional polypeptide. RNA ligase enzyme joins two exons together via phosphodiester bond between 3’ hydroxyl at the end of one exon and a 5’ phosphate at the end of another exon. The correct answer is D.
Multiple choice dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

How many types of RNA polymerases are operative in eukaryotes?

  1. Four

  2. Three

  3. Two

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

Eukaryotes have three RNA polymerases which are structurally distinct complexes, though share certain subunits in common, and have a specific function and specific promoter sequence. RNA polymerase I synthesize preribosomal RNA (pre-rRNA), which contains the precursor for the 18S, 5.8S, and 28S rRNAs. RNA polymerase II is synthesized mRNAs and some specialized RNAs. RNA polymerase III makes tRNAs, the 5S rRNA, and some other small specialized RNAs. Option B is correct.

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

DNA polymerase enzyme is required for the synthesis of 

  1. RNA from DNA

  2. DNA from DNA

  3. RNA from RNA

  4. DNA from RNA
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

DNA polymerase is an enzyme that synthesizes DNA molecules from deoxynucleotides, the building blocks of DNA. It helps in DNA replication (DNA dependent DNA synthesis). This enzyme works in pairs to create two complementary DNA strands from a single original DNA molecule.

RNA from DNA (transcription) is synthesized by RNA polymerase.
DNA from RNA is synthesized by reverse transcriptase enzyme in some viruses.
So, the correct option is 'DNA from DNA'.

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

Consider the following statements and choose the correct option.

In eukaryotes
(i) RNA polymerase I transcribes rRNA.
(ii) RNA polymerase I transcribes snRNA.
(iii) RNA polymerases II transcribes tRNA.
(iv) RNA polymerase II transcribes hnRNA.

  1. 1 and 2 are correct.

  2. 1 and 3 are correct.

  3. 1, 2 and 4 are correct.

  4. 2 and 3 are correct.

  5. 1 and 4 are correct.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Eukaryotes have three RNA polymerases which are structurally distinct complexes, though share certain subunits in common, and have a specific function and specific promoter sequence. RNA polymerase I synthesize preribosomal RNA (pre-rRNA), which contains the precursor for the 18S, 5.8S, and 28S rRNAs.

RNA polymerase II transcribes the presursor of mRNA which is heterogenous RNA (hnRNA). 
RNA polymerase III makes tRNAs, the 5S rRNA, and sNRNAs. 
Therefore, the correct answer is option (E).

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

Choose the correct answers from the alternatives given :
RNA polymerase

  1. can produce several polypeptide chains at one time through the creation of polysomes

  2. starts transcribing at an AUG triplet on one DNA strand

  3. transcribes both introns and exons
  4. transcribes both DNA strands, but always in a $5' \, \rightarrow \, 3'$ direction
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

RNA polymerase transcribes both exons and introns present in DNA which are consecutively present in the RNA too, although, introns are removed by splicing in a mature mRNA. Exons are the segment of the genetic material or DNA/RNA that code for an amino acid but introns do not code for any amino acid sequence or protein. Introns have a regulatory function in both replication and transcription processes.

So, the correct option is 'transcribes both introns and exons'.

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

DNA polymerase enzyme is required for the synthesis of

  1. RNA from DNA

  2. DNA from DNA

  3. RNA from RNA

  4. DNA from RNA
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

DNA polymerase enzyme helps in DNA dependent DNA synthesis by addition of deoxyribonucleotides, building blocks of DNA. This enzyme uses DNA as the template and synthesizes DNA. This process is also known as replication.

RNA from DNA is synthesized by RNA polymerase enzyme through the process called transcription. RNA is used as the template and nucleotides are for RNA synthesis. 
DNA from RNA is synthesized by reverse transcriptase enzyme in some retroviruses where RNA acts as the genetic material.
So, the correct option is 'DNA from DNA'.

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

Which of the following statements are correct?
(i) RNA polymerase I transcribes rRNAs.
(ii) RNA polymerase II transcibes snRNAs.
(iii) RNA polymerase III transcibes hnRNA,
(iv) RNA polymerase II transcribes hnRNA.

  1. (i) and (ii)

  2. (i) and (iii)

  3. (i), (ii) and (iv)

  4. (i) and (iv)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

RNA polymerase 1 (also known as Pol I) is, in higher eukaryotes, the polymerase that only transcribes ribosomal RNA (but not 5S rRNA, which is synthesized by RNA polymerase III), a type of RNA that accounts for over 50% of the total RNA synthesized in a cell. Pol I is a 590 kDa enzyme that consists of 14 protein subunits (polypeptides). Twelve of its subunits have identical or related counterparts in RNA polymerase II (Pol II) and RNA polymerase III (Pol III). The other two subunits are related to Pol II initiation factors and have structural homologues in Pol III. Ribosomal DNA transcription is confined to the nucleolus, where about 400 copies of the 42.9-kb rDNA gene are present, arranged as tandem repeats in nucleolus organizer regions. Each copy contains a 13.3 kb sequence encoding the 18S, the 5.8S, and the 28S RNA molecules, interlaced with two internal transcribed spacers, ITS1 and ITS2, and flanked upstream by a 5' external transcribed spacer and a downstream 3' external transcribed spacer. Because of the simplicity of Pol I transcription, it is the fastest-acting polymerase and contributes up to 60% of cellular transcription levels in exponentially growing cells.

RNA polymerase II (RNAP II and Pol II) is a multiprotein complex. It is one of the three RNAP enzymes found in the nucleus of eukaryotic cells. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoters and begin transcription. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoters and begin transcription.
So the correct option is ' (i) and (ii)'.

Multiple choice biology respiration and energy transfer respiratory quotient-basic respiration-plants respiratory quotient

R.Q. stands for

  1. Resistance coefficient

  2. Replicase concentration

  3. Respiratory quotient

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

Respiratory quotient (RQ) is the ratio of the volume of carbon dioxide released to the volume of oxygen taken in respiration in the given period of time at standard temperature and pressure. 

RQ = CO2 eliminated / O2 consumed

Name of the substance Respiratory Quotient
Carbohydrates 1
Proteins 0.8 - 0.9
Triolein 0.7
Tripalmitin (Fat) 0.7
Malic acid 1.33
Tartaric acid 1.6
Oxalic acid 4.0

Thus, the correct answer is option C. 


Multiple choice expression of gene inherited changes biology

RNAi is the important cellular defence in

  1. Prokaryotes

  2. Eukaryotes

  3. All living organism

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

Inactivation of RNA by using another RNA is called RNA interference(RNAi). It is used in pest control in tomato plant. It is a cellular defence method. It is applicable to eukaryotes only.

So, the correct option is ‘Eukaryotes’.

Multiple choice expression of gene inherited changes biology

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

  1. Transcription Initiation

  2. Processing level

  3. Transport of mRNA

  4. Translation level
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A DNA segment that contributes to phenotype/function is called gene. In prokaryotes, the predominant site for control of gene expression is at Transcription level, where as in eukaryotes, control of gene expression occurs at transcription level, processing level, transport of mRNA, translation level.

So, the correct option is ‘Transcription intiations’.

Multiple choice expression of gene inherited changes biology

Initiating codon in eukaryotes is

  1. AUG

  2. GUG

  3. UGA

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

In eukaryotes, the translation process begins at the start codon AUG, which codes for the amino acid methionine.

Multiple choice expression of gene inherited changes biology

Gene which is responsible for the synthesis of a polypeptide chain is called as

  1. Promotor gene

  2. Structural gene

  3. Regulator gene

  4. Operator gene
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Promoter is a DNA segment that serves to initiate transcription of a particular gene. They are present upstream near the transcription start sites of genes. Regulator gene regulates the expression of structural genes by its protein product 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. Operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as repressor protein binding site. The gene that codes for any RNA / protein product which do not serve as regulatory protein are known as structural genes. The lac Z lac Y and lac A genes in lac operon are the structural genes. Option B is the correct answer.