ROUTERA

Chapter 6 Molecular basis of Inheritance

Class 12th Biology Chapter hots

1. Explain the structure of DNA as proposed by Watson and Crick. How does this structure explain the mechanism of replication?

Answer:
Structure of DNA:

  • Double helix model with two antiparallel strands.
  • Backbone of deoxyribose sugar and phosphate; nitrogen bases (A-T and G-C) form rungs of the ladder.
  • Base pairs are held by hydrogen bonds (A-T = 2 bonds; G-C = 3 bonds).

Replication Mechanism:

  • Semi-conservative model.
  • Parent strands act as templates.
  • DNA polymerase adds nucleotides complementary to the template strands.
  • Ensures genetic continuity.

2. Compare and contrast prokaryotic and eukaryotic DNA replication. How is replication regulated in these systems?

Answer:

Molecular basis of Inheritance

Regulation:

  • Prokaryotes: Controlled by initiation proteins like DnaA.
  • Eukaryotes: Regulated by cyclins and CDKs to ensure replication occurs once per cycle.

3. Describe the Meselson and Stahl experiment. How did it confirm the semi-conservative mode of DNA replication?

Answer:
Experiment:

  • Grew E. coli in 15N (heavy nitrogen) medium, then shifted to 14N.
  • Isolated DNA after one and two generations.
  • Used density gradient centrifugation to analyze DNA.

Findings:

  • First generation: Hybrid DNA (one strand 15N, one 14N).
  • Second generation: 50% hybrid and 50% light DNA.

Conclusion:
Supported the semi-conservative model, where each daughter DNA has one parent strand and one newly synthesized strand.

4. Discuss the role of enzymes in DNA replication. Why is proofreading critical for maintaining genetic integrity?

Answer:
Enzymes:

  1. Helicase: Unwinds DNA helix.
  2. Topoisomerase: Relieves supercoiling.
  3. Primase: Synthesizes RNA primers.
  4. DNA Polymerase: Adds nucleotides and proofreads.
  5. Ligase: Joins Okazaki fragments.

Proofreading:

  • Ensures base-pairing accuracy.
  • Reduces mutation rates.
  • DNA polymerase detects and replaces incorrect nucleotides, maintaining fidelity.

5. What are the differences between DNA and RNA in terms of structure and function?

Answer:

Molecular basis of Inheritance

6. Explain the concept of the genetic code. Why is it described as universal, degenerate, and unambiguous?

Answer:
Genetic Code Features:

  • Universal: Same codons specify the same amino acids in all organisms.
  • Degenerate: Multiple codons code for the same amino acid (e.g., UUU and UUC for phenylalanine).
  • Unambiguous: Each codon specifies only one amino acid.

Importance:

  • Facilitates translation of genetic information into proteins.

7. How does transcription differ between prokaryotes and eukaryotes?

Answer:

Molecular basis of Inheritance

8. Discuss the process of translation. How is it regulated?

Answer:
Translation Steps:

  1. Initiation: mRNA binds to the ribosome, and the start codon (AUG) is recognized.
  2. Elongation: tRNA brings amino acids, which are linked by peptide bonds.
  3. Termination: Stop codons (UAA, UAG, UGA) signal the end.

Regulation:

  • Availability of mRNA and ribosomes.
  • Translational repressors or enhancers.

9. What is the role of operons in prokaryotic gene regulation? Explain using the lac operon.

Answer:
Lac Operon:

  • Regulates lactose metabolism in E. coli.
  • Inducible system: Active only in the presence of lactose.
  • Components: Promoter, operator, structural genes (lacZ, lacY, lacA).

Mechanism:

  • Lactose binds to the repressor, deactivating it.
  • RNA polymerase transcribes structural genes.

10. Explain the concept of epigenetic regulation with examples.

Answer:
Epigenetics:

  • Modifications that do not change DNA sequence but affect gene expression.
  • Example: DNA methylation silences genes; histone acetylation activates genes.

11. How does the human genome project contribute to understanding molecular inheritance?

Answer:

  • Sequenced the entire human genome.
  • Identified gene functions and regulatory elements.
  • Facilitates the study of genetic disorders and personalized medicine.

12. Discuss the differences between coding and non-coding DNA. Why is non-coding DNA important?

Answer:

Molecular basis of Inheritance

13. Describe the role of small RNAs in gene regulation.

Answer:
Types:

  • miRNA: Inhibits translation.
  • siRNA: Degrades target mRNA.

Significance:

  • Fine-tunes gene expression.
  • Protects against viral RNA.

14. Explain the steps of recombinant DNA technology and its applications.

Answer:
Steps:

  1. Isolation of DNA.
  2. Cutting with restriction enzymes.
  3. Ligation into vectors.
  4. Introduction into host cells.

Applications:

  • Gene therapy, GM crops, vaccine development.

15. How does mutation alter the DNA sequence? Discuss types of mutations.

Answer:
Types:

  1. Point Mutation: Single base change.
  2. Frameshift Mutation: Insertion or deletion shifts the reading frame.
  3. Silent Mutation: No amino acid change.

16. What are transposons? How do they contribute to genetic variation?

Answer:
Transposons: Mobile genetic elements that can move within the genome.
Impact: Cause mutations, gene rearrangements, and regulatory changes.

17. How is the lac operon regulated by glucose levels?

Answer:

  • Catabolite Repression: High glucose reduces cAMP, inactivating CAP.
  • Lac operon remains off despite lactose presence.

18. Discuss the process and significance of splicing in eukaryotes.

Answer:

  • Removes introns, joins exons.
  • Ensures accurate mRNA for translation.
  • Alternative splicing generates protein diversity.

19. Explain the significance of telomerase in maintaining chromosome integrity.

Answer:

  • Adds repetitive sequences to telomeres.
  • Prevents loss of essential genes during replication.

20. How does RNA interference work?

Answer:

  • siRNA binds to complementary mRNA.
  • Triggers mRNA degradation, silencing gene expression.

21. What is the role of restriction enzymes in genetic engineering?

Answer:

  • Cuts DNA at specific sequences.
  • Generates sticky or blunt ends for ligation.

22. Discuss the impact of single nucleotide polymorphisms (SNPs) on genetic traits.

Answer:

  • SNPs are variations in a single nucleotide.
  • Affect disease susceptibility and drug responses.

23. How does DNA packaging in eukaryotes differ from prokaryotes?

Answer:

  • Eukaryotes: DNA wrapped around histones (chromatin).
  • Prokaryotes: Naked circular DNA.

24. What are the applications of bioinformatics in studying molecular inheritance?

Answer:

  • Analyzing genomic data.
  • Predicting protein structures.
  • Understanding evolutionary relationships.

25. How is the Central Dogma of molecular biology modified by reverse transcription?

Answer:

  • Central Dogma: DNA → RNA → Protein.
  • Reverse Transcription: RNA → DNA (e.g., retroviruses like HIV).