Biology

Molecular Genetics

917 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 cloning experiments, cDNA molecules can be obtained from an mRNA copy by

  1. Polymerase chain reaction

  2. Reverse transcriptase

  3. Ribozyme

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

Complementary DNA (cDNA) is a DNA copy of a messenger RNA (mRNA) molecule produced by reverse transcriptase. cDNA is often used to clone eukaryotic genes in prokaryotes.  cDNA is also produced naturally by retroviruses (such as HIV) for integration into the host's genome.

So, the correct option is 'Reverse transcriptase'.

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

Choose the correct answers from the alternatives given :
The central dogma of molecular biology

  1. states that DNA is a template for all RNA production

  2. pertains only to prokaryotes because humans are unique

  3. states that translation precedes transcription

  4. states that DNA is a template only for DNA replication
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

During the transcription phase of the central dogma, DNA acts as the template for RNA synthesis. The RNA polymerase enzyme identifies the base on the DNA strand and adds a complementary base to the sequence. After transcription, translation of mRNA occurs that leads to the formation of the polypeptide sequence.

So, the correct option is 'states that DNA is a template for all RNA production'.

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

During transcription, the site of DNA molecule at which RNA polymerase binds is called

  1. promoter

  2. regulator

  3. receptor

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

The RNA polymerase enzyme binds to a specific site called promoter and initiates transcription. The promoter region determines which DNA strand is to be transcribed. Thus, a promoter region has RNA polymerase recognition site and RNA polymerase binding site.

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

The molecule needed to allow a cell to transfer genetic information from RNA to DNA, is

  1. DNA polymerase

  2. RNA polymerase

  3. reverse transcriptase

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

Reverse transcriptase is an enzyme used to generate complementary DNA from an RNA template, a process termed reverse transcription. Reverse transcriptase enzymes can be found in viruses, which use reverse transcriptase to make more viruses. 

So, the correct option is 'reverse transcriptase'.

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

Silencing of a gene could be achieved through the use of

  1. RNAI only

  2. Antisense RNA only

  3. Both RNAi and antisense RNA

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing). The source of this complementary RNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate.
So, the correct answer is 'Both RNAi and antisense RNA'.
Multiple choice bio-chemistry nucleic acids central dogma transcription and gene expression molecular biology

Which of the following is correct match of phenomenon and its explanation?

  1. Central dogma$\rightarrow$ RNA$\rightarrow$ DNA $\rightarrow$ Protein$\rightarrow$ RNA
  2. Reverse transcription$\rightarrow$ PCR$\rightarrow$ DNA amplification
  3. Transcription$\rightarrow$ Formation of RNA and proteins
  4. RNA silencing$\rightarrow$ Use of dsRNA
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Reverse transcription polymerase chain reaction (RT-PCR) uses mRNA rather than DNA as the starting template. First, the enzyme reverse transcriptase uses the mRNA template to produce a complementary single-stranded DNA strand called cDNA in a process known as reverse transcription. Next, DNA polymerase is used to convert the single-stranded cDNA into double-stranded DNA. These DNA molecules can now be used as templates for a polymerase chain reaction ( PCR ) for DNA amplification.

Central dogma can be correctly represented as DNA→ DNA→ RNA → Protein. 
Transcription is the formation of RNA from DNA. 

So, the correct option is 'Reverse transcription→ PCR→ DNA amplification'.
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'.