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

The triplet sequence of gene expression by codons is associated with which of the following types of mutations?

  1. Frameshift mutation

  2. Nonsense mutation

  3. Missense mutations

  4. Neutral mutation

  5. Silent mutations
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A frameshift mutation is a genetic mutation caused by indels (insertions or deletions) of a number of nucleotides in a DNA sequence that is not divisible by three. Due to the triplet nature of gene expression by codons, the insertion or deletion can change the reading frame .

Multiple choice

Alternative splicing is a regulated process during gene expression that results in a single gene coding for multiple proteins. Which of the following events does NOT occur in alternative splicing during gene expression?

  1. The exons to be retained in the mRNA are determined during the splicing process.

  2. U3 is not involved in mRNA splicing.

  3. Splicing silencers are sites to which splicing repressor proteins bind.

  4. Splicing is regulated by trans-acting proteins.

  5. Each intron has GU at its 3' end.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The typical eukaryotic nuclear intron has consensus sequences defining important regions.  Near the 3' end there is a branch site.

Multiple choice

In humans the complementary DNA (cDNA) is, DNA synthesised from a mature mRNA template. Which of the following statements regarding the synthesis of complementary DNA (cDNA) is INCORRECT?

  1. It is likely that the ssDNA forms a hairpin loop at the 3' end.

  2. DNA polymerase is added, along with deoxynucleotide triphosphates.

  3. A poly-T oligonucleotide primer is hybridised onto the poly-A tail of the mature mRNA template.

  4. The mixture of mature mRNA strands is extracted from the cell.

  5. A eukaryotic cell transcribes the DNA into RNA.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Reverse transcriptase is added, along with deoxynucleotide triphosphates (A, T, G, C). This synthesises one complementary strand of DNA hybridised to the original mRNA strand.

Multiple choice

The functional unit of gene which synthesizes one polypeptide for protein synthesis is termed as

  1. replicon

  2. muton

  3. codon

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

A cistron is the functional unit of a gene that codes for a single polypeptide chain. A replicon is a DNA unit capable of replication, a muton is the smallest mutable unit, and a codon is a triplet coding for one amino acid. Cistron aligns with the 'one gene-one polypeptide' concept.

Multiple choice

Small nuclear RNAs (Sn RNAs) are involved in the eukaryotic

  1. transcription

  2. replication

  3. reverse transcriptase

  4. transfer of amino acid

  5. splicing of mRNA
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Splicing is a modification of the nascent pre-messenger RNA (pre-mRNA) transcript in which introns are removed and exons are joined. In this process, snRNAs are used.

Multiple choice

The small cytoplasmic RNAs (sc RNAs) in the form of sc RNPs constitute the

  1. mRNAs

  2. signal recognition particle

  3. small nucleolar RNA

  4. ribosomal RNAs

  5. t RNAs
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The signal recognition particle (SRP) is an abundant, cytosolic, universally conserved ribonucleoprotein (protein-RNA complex) that recognizes and targets specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes.

Multiple choice

Which of the following is of great importance in genetics?

  1. Penicillium

  2. Cleviceps

  3. Neurospora

  4. Both of (a) and (b)

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Neurospora (red bread mold) was instrumental in establishing the one gene-one enzyme hypothesis through Beadle and Tatum's Nobel Prize-winning experiments. It became a model organism for genetic research due to its rapid life cycle and haploid nature, making genetic analysis straightforward. Penicillium is an antibiotic-producing fungus, and 'Cleviceps' appears to be a misspelling of Claviceps (ergot fungus), neither of which are foundational to genetics research.

Multiple choice

Viruses have:

  1. RNA

  2. DNA

  3. either RNA or DNA

  4. neither DNA nor RNA

  5. none of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Viruses are classified as either RNA viruses or DNA viruses based on their genetic material. A virus contains either RNA or DNA, but never both simultaneously. This fundamental distinction is crucial for understanding viral replication mechanisms, classification, and the development of antiviral strategies. Option C correctly captures this binary characteristic of viral genomes.

Multiple choice

Which of the following is not involved in translation?

  1. m-RNA

  2. t-RNA

  3. DNA

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

Translation is the process of protein synthesis where mRNA is decoded by ribosomes to produce a polypeptide chain. This process requires mRNA (as the template), tRNA (as the adapter molecule bringing amino acids), and amino acids (as building blocks). DNA is involved in transcription (making mRNA) but not directly in translation, which occurs in the cytoplasm (or prokaryotic cytoplasm).

Multiple choice

Prions consist of

  1. DNA and RNA

  2. DNA, RNA and proteins

  3. RNA and proteins

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

 A prion is an infectious agent, composed entirely of protein.

Multiple choice

Termination of amino acid chain requires codons

  1. UAG, UAA, UGA

  2. UUU, GGU, UGG

  3. GUG, UGG, AUG

  4. UGG, GGG, AUG
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

UAG, UAA, and UGA are the three stop/termination codons in the genetic code that signal the end of protein synthesis during translation. The other options contain codons that code for specific amino acids.

Multiple choice

Which one of the following is correct for virus?

  1. They have DNA or RNA

  2. They replicate inside the animal cell only

  3. They are living

  4. They are bigger than bacteria
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Viruses have either DNA or RNA as genetic material, never both. This is a fundamental viral characteristic. Option B is wrong because viruses replicate in various cells (plant, animal, bacterial), not just animal cells. Option C is wrong because viruses are not considered fully living (they need host cells). Option D is wrong because viruses are much smaller than bacteria.