Class 12/Question Bank/Competency Based
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
BioNotesBioNotesCreated by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Competency Based Questions on Molecular Basis of Inheritance
1. Analyze the Experiment: In the Hershey-Chase experiment, bacteriophages were labeled with radioactive sulfur (³⁵S) and allowed to infect bacteria. After blending and centrifugation, where would you expect to find the radioactivity? a) Inside the bacterial pellet. b) In the supernatant fluid. c) Inside the bacterial DNA. d) Attached to the bacterial cell wall.
2. Calculate: A double-stranded DNA molecule has 20% Adenine. According to Chargaff's rule, what is the percentage of Cytosine? a) 20% b) 30% c) 40% d) 80%
3. Predict the Consequence: A mutation changes a codon in mRNA from UAC (Tyrosine) to UAA. What will be the immediate effect on translation? a) The protein will be longer than normal. b) The protein synthesis will stop prematurely (Nonsense mutation). c) A different amino acid will be incorporated (Missense mutation). d) There will be no change in the protein (Silent mutation).
4. Assertion (A): The leading strand in DNA replication is synthesized continuously, while the lagging strand is synthesized discontinuously. Reason (R): DNA Polymerase can only synthesize DNA in the 5' → 3' direction. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is not the correct explanation of A. c) A is true but R is false. d) A is false but R is true.
5. Molecular Mechanism: Why is RNA less stable than DNA? a) RNA is single-stranded and lacks thymine. b) RNA has a 2'-OH group in ribose which makes it reactive and catalytic. c) RNA contains Uracil which pairs with Adenine less strongly. d) RNA polymerase is error-prone.
6. Gene Regulation: In the Lac Operon, what happens if both Glucose and Lactose are present in the medium? a) The operon is fully active. b) The operon is inactive or expressed at a very low level (Catabolite repression). c) The repressor binds tightly to the operator. d) The lacZ gene is mutated.
7. Identify the Process: A researcher isolates a mature mRNA from a eukaryote and compares it with the genomic DNA gene sequence. She notices that the mRNA is much shorter than the gene. This is due to: a) Capping b) Tailing c) Splicing (removal of introns) d) Mutation
8. Sequence Analysis: If the sequence of the coding strand of DNA is 5'-ATGCCTAG-3', what will be the sequence of the transcribed mRNA? a) 3'-TACGGATC-5' b) 5'-AUGCCUAG-3' c) 5'-TACGGATC-3' d) 3'-AUGCCUAG-5'
9. Forensic Application: Two individuals are suspected in a crime. DNA fingerprinting using VNTRs is performed. Why are VNTRs suitable for identification? a) They code for essential proteins. b) They are highly conserved across the population. c) They show high degree of polymorphism (variation in repeat number) between individuals. d) They are mitochondrial DNA sequences.
10. Central Dogma: Which of the following violates the classic Central Dogma of molecular biology? a) Replication of DNA in E. coli. b) Transcription of tRNA in humans. c) Reverse transcription in HIV. d) Translation of insulin protein.
11. Structural Biology: The 'beads-on-string' structure seen under an electron microscope refers to: a) Ribosomes on mRNA (Polysome). b) Nucleosomes in chromatin. c) Spliceosomes on hnRNA. d) DNA polymerase on the replication fork.
12. Genetic Code: The genetic code is "degenerate". This means: a) One codon codes for multiple amino acids. b) One amino acid is coded by multiple codons. c) The code is ambiguous. d) The code varies between species.
13. Experimental Logic: Meselson and Stahl used ¹⁵N and ¹⁴N to prove semi-conservative replication. If they had allowed the bacteria to divide for two generations in ¹⁴N medium (after growing in ¹⁵N), what ratio of DNA bands would they observe in the CsCl gradient? a) 100% Hybrid (¹⁵N-¹⁴N). b) 50% Hybrid, 50% Light (¹⁴N-¹⁴N). c) 25% Heavy, 75% Light. d) 50% Heavy, 50% Hybrid.
14. Enzyme Function: Which enzyme is responsible for removing the RNA primer and replacing it with DNA nucleotides during replication in prokaryotes? a) DNA Polymerase I b) DNA Polymerase III c) Primase d) Ligase
15. HGP: One of the surprising findings of the Human Genome Project was: a) Humans have over 100,000 genes. b) More than 98% of the genome does not code for proteins. c) Every individual has a completely unique genome sequence (0% similarity). d) Chromosome Y has the most genes.
E. coli bacteria are growing in a culture medium containing glucose. A researcher suddenly adds lactose to the medium and removes glucose.
16. Explain: Before the addition of lactose, where was the Repressor protein located? a) Bound to the Promoter. b) Bound to the Operator. c) Bound to the structural genes. d) Free in the cytoplasm.
17. Mechanism: How did the addition of lactose trigger the production of the enzyme? a) Lactose bound to the DNA polymerase. b) Lactose (Allolactose) bound to the Repressor, causing it to change shape and release the Operator. c) Lactose mutated the lacI gene. d) Lactose acted as a co-factor for the enzyme.
18. Application: If a mutation occurred in the lacI gene (regulatory gene) such that the Repressor protein could no longer bind to the Operator, what would be the status of the lac operon? a) Constitutively ON (always active). b) Permanently OFF. c) Inducible only by high concentrations of lactose. d) It would transcribe only lacZ but not lacY.
A scientist is studying a gene "X" in eukaryotic cells. The gene DNA is 5000 base pairs long. However, the mature mRNA found in the cytoplasm is only 1500 bases long.
19. Identify: What biological process accounts for the size difference between the gene and the mRNA? a) Replication error. b) RNA Splicing (Removal of Introns). c) Protein degradation. d) Translation termination.
20. Reasoning: Are the 3500 missing bases "junk" DNA? a) Yes, they have no function. b) No, they were Introns, which may have regulatory roles or allow for alternative splicing (evolutionary flexibility). c) They were signal peptides. d) They were destroyed by DNase.
21. Contrast: If this gene "X" were taken from the eukaryote and inserted directly into a bacterium (E. coli), would the bacterium produce the correct functional protein? a) Yes, the genetic code is universal. b) No, bacteria lack the machinery to splice out introns, so the protein would be incorrect/non-functional. c) Yes, but at a slower rate. d) No, bacteria cannot transcribe eukaryotic DNA.
A crime scene sample (blood) is collected. DNA is isolated and subjected to DNA Fingerprinting. Suspect B's banding pattern matches the crime scene sample perfectly.
22. Analyze: Which specific regions of the DNA are responsible for these unique banding patterns? a) The coding regions (Exons). b) The promoter regions. c) Variable Number Tandem Repeats (VNTRs) / Satellite DNA. d) The mitochondrial DNA.
23. Technique: Which technique was likely used to multiply the small amount of DNA from the blood sample before testing? a) Gel Electrophoresis. b) PCR (Polymerase Chain Reaction). c) Southern Blotting. d) Centrifugation.
24. Evaluate: Can this technique distinguish between identical twins? a) Yes, their VNTRs are different. b) No, identical twins have identical DNA/VNTR patterns. c) Yes, but only using mitochondrial DNA. d) No, unless one has a mutation.
25. Designing an Experiment: You want to prove that DNA replication is semi-conservative in a human cell line (not bacteria).
26. Visualizing the Process: Create a flowchart showing the "Central Dogma" in a eukaryotic cell vs. a retrovirus.
27. Formulating a Hypothesis: Observation: The genetic code is "degenerate" (e.g., Leucine is coded by 6 different codons).
28. Decoding a Sequence: Template DNA strand: 3' - T A C C G A T C C A T T - 5'
29. Critical Analysis: "The Human Genome Project revealed that 99.9% of nucleotide bases are exactly the same in all people."
30. Scenario Analysis (Mutation): A frameshift mutation occurs near the end of a gene versus the beginning.
31. Developing a Model: Design a physical analogy for the Lac Operon.