Complete Summary and Solutions for Molecular Basis of Inheritance – NCERT Class XII Biology, Chapter 5 – DNA Structure, Replication, Transcription, Genetic Code, Human Genome Project

Comprehensive summary and explanation of Chapter 5 'Molecular Basis of Inheritance' from the NCERT Class XII Biology textbook, covering DNA and RNA structure, discovery of genetic material, DNA replication, transcription, genetic code, translation, gene expression regulation, Human Genome Project, DNA fingerprinting, and answers to all textbook exercises.

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Categories: NCERT, Class XII, Biology, Chapter 5, Genetics, DNA, RNA, Molecular Biology, Replication, Transcription, Translation, Human Genome Project, Summary, Questions, Answers

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Molecular Basis of Inheritance - Class 12 NCERT Chapter 5 - Ultimate Study Guide, Notes, Questions, Quiz 2025

Full Chapter Summary & Detailed Notes - Molecular Basis of Inheritance Class 12 NCERT

Overview & Key Concepts

Chapter Goal: Explore the structure and function of genetic material (DNA/RNA), from discovery to processes like replication, transcription, translation, and regulation. Exam Focus: Diagrams (DNA helix, replication fork, genetic code table), experiments (Griffith, Hershey-Chase), calculations (e.g., DNA length). 2025 Updates: Emphasis on genomics applications, CRISPR ties to regulation. Fun Fact: Watson-Crick model (1953) revolutionized biology. Core Idea: DNA as hereditary blueprint; flow DNA → RNA → Protein (Central Dogma). Real-World: DNA fingerprinting in forensics; HGP for medicine. Ties: Links to inheritance (Ch4), evolution (Ch7). Expanded: All subtopics (5.1-5.10) covered point-wise with diagram descriptions, principles, steps, and biotech relevance for visual/conceptual learning. Additional: RNA World hypothesis, lac operon details for regulation.
Wider Scope: From molecular structure to genome projects; role in understanding heredity, mutations, and biotechnology.
Expanded Content: Detailed experiments, base pairing rules, enzyme roles in processes; e.g., semi-conservative replication proof, codon degeneracy.

Fig. 5.1: A Polynucleotide Chain (Description)

Linear chain showing nucleotides linked by 3'-5' phosphodiester bonds: Phosphate-sugar backbone with bases (A, T, G, C) projecting; 5' phosphate end and 3' OH end labeled. Visual: Zigzag backbone with bases as side arms.

5.1 The DNA

Introduction: DNA as long polymer of deoxyribonucleotides; length defines organism (e.g., φX174: 5386 nt, E. coli: 4.6×10^6 bp, human: 3.3×10^9 bp).
Biotech Relevance: Basis for cloning, sequencing in recombinant DNA tech.

Fig. 5.2: Double Stranded Polynucleotide Chain (Description)

Two anti-parallel strands (5'→3' and 3'→5') with base pairs (A-T 2 H-bonds, G-C 3 H-bonds); sugar-phosphate backbone outside, bases inside ladder. Visual: Antiparallel arrows, H-bonds as dashed lines.

5.1.1 Structure of Polynucleotide Chain

Components: Nucleotide = nitrogenous base (purines: A/G; pyrimidines: C/T/U), pentose sugar (deoxyribose in DNA, ribose in RNA), phosphate.
Linkages: N-glycosidic (base to C1' sugar), phosphodiester (5' phosphate to 3' OH).
RNA Differences: 2' OH group (labile), U instead of T; uracil at thymine position.
History: Meischer (1869) isolated 'nuclein'; Watson-Crick (1953) double helix from X-ray (Wilkins/Franklin) and Chargaff's rules (A=T, G=C).
Salient Features of Double Helix: Two anti-parallel polynucleotide chains; bases inside H-bonded (A-T, G-C); right-handed, 3.4 nm pitch, 10 bp/turn, 0.34 nm/bp; stacking stabilizes.
Implications: Complementary strands predict sequence; semi-conservative replication; Central Dogma: DNA → RNA → Protein (reverse in retroviruses: transcription?).

Fig. 5.3: DNA Double Helix (Description)

3D helical model: Twisted ladder with base pairs as rungs, sugar-phosphate rails; shows uniform width due to purine-pyrimidine pairing. Visual: Ribbon-like twist, ~2 nm diameter.

Fig. 5.4a: Nucleosome (Description)

Histone octamer (H2A, H2B, H3, H4 dimers) core with DNA wrapped ~1.65 turns (147 bp); H1 linker histone. Visual: Bead-like structure with DNA coil.

Fig. 5.4b: EM Picture - ‘Beads-on-String’ (Description)

Electron micrograph: Chromatin as string of nucleosomes (beads) connected by linker DNA (~50 bp). Visual: Periodic beads ~11 nm diameter on 30 nm fiber.

5.1.2 Packaging of DNA Helix

Prokaryotes: DNA in nucleoid loops held by proteins (e.g., E. coli: 1.36 mm, ~4.6×10^6 bp).
Eukaryotes: Histones (basic, lysine/arginine rich) form octamer; DNA wraps to nucleosome (200 bp); 'beads-on-string' chromatin.
Higher Packaging: 30 nm solenoid fiber → looped domains → metaphase chromosomes; Non-histone chromosomal (NHC) proteins assist; euchromatin (loose, active), heterochromatin (dense, inactive).
Calculation Example: Human DNA ~2 m; ~25,000 nucleosomes per chromosome.
Biotech Relevance: Epigenetics in gene therapy; chromatin remodeling for expression.

5.2 The Search for Genetic Material

Historical Context: Mendel (1860s) factors unknown; Sutton/Morgan chromosomes; molecular quest by 1920s.

Fig. 5.5: The Hershey-Chase Experiment (Description)

Blender experiment: ³²P-labeled DNA phages infect bacteria (radioactive pellet); ³⁵S-labeled protein (radioactive supernatant). Steps: Infection, blending, centrifugation. Visual: Split diagram showing DNA entry, protein coat removal.

Transforming Principle

Griffith (1928): S (smooth, virulent, coated) vs. R (rough, non-virulent) Streptococcus pneumoniae; heat-killed S + live R → live S in mice; 'transforming principle' transfers virulence.
Steps: Inject variants, observe transformation; recovered live S from dead mice.
Implication: Genetic material transferable, heat-stable.

Biochemical Characterisation of Transforming Principle

Avery, MacLeod, McCarty (1944): Purified from heat-killed S; DNA transforms R to S; proteases/RNases no effect, DNase inhibits.
Conclusion: DNA as hereditary material (not all convinced, thought proteins).

5.2.1 The Genetic Material is DNA

Hershey-Chase (1952): Bacteriophages (T2) with ³²P-DNA or ³⁵S-protein; DNA enters E. coli, protein stays outside; progeny phages radioactive from DNA.
Steps: Label, infect, blend (remove coats), centrifuge (pellet bacteria); radioactivity in pellet for DNA, supernatant for protein.
Proof: Unequivocal DNA as genetic material.

5.2.2 Properties of Genetic Material (DNA vs RNA)

Criteria: Replicate accurately; chemically/structurally stable; allow mutations for evolution; express as Mendelian characters.
DNA Advantages: Double helix stable (complementary strands reanneal); less reactive (no 2' OH); T (methylated U) protects from UV damage/repair.
RNA Drawbacks: Single-stranded, labile (2' OH reactive, catalytic); mutates faster (viruses evolve quickly).
Expression: RNA direct (messenger/adapter); DNA via RNA; both replicate via base pairing.
RNA as Genetic Material: Some viruses (TMV, QB); fulfills criteria but less stable.
Biotech Relevance: mRNA vaccines (COVID); RNA interference therapy.

5.3 RNA World

Hypothesis: Early life RNA as both genetic material and catalyst (ribozymes); preceded DNA-protein world; self-replicating RNA evolved to DNA for stability.
Evidence: Ribosomes RNA catalytic; viroids (naked RNA) replicate.
Expanded: RNA editing, splicing; relevance to origin of life, synthetic biology.

5.4 Replication

Semi-Conservative: Each strand template; Meselson-Stahl (1958) proved via ¹⁵N/¹⁴N density gradient.
Enzymes: Helicase unwinds; SSB proteins stabilize; topoisomerase relieves strain; primase (RNA primer); DNA pol III elongates (5'→3'); DNA pol I removes primer; ligase seals.
Steps: Initiation (origin), elongation (forks bidirectional), termination (replisome).
Prokaryotic vs Eukaryotic: Multiple origins in eukaryotes; telomeres (telomerase).
Diagram Note: Replication fork: Leading (continuous), lagging (Okazaki fragments 100-200 nt).
Biotech Relevance: PCR mimics replication.

5.5 Transcription

Process: DNA → mRNA; RNA pol binds promoter (TATA box), unwinds, synthesizes 5'→3' complementary (U for A).
Steps: Initiation (sigma factor in prok), elongation, termination (rho-independent hairpin).
Post-Transcription: Capping (7-methyl G), tailing (poly A), splicing (introns out).
Prok vs Euk: Coupled in prok; nuclear in euk; multiple pol (I rRNA, II mRNA, III tRNA).
Biotech Relevance: Antisense RNA for gene silencing.

5.6 Genetic Code

Features: Triplet (64 codons), degenerate (multiple for AA), unambiguous, universal, comma-less, start (AUG Met), stop (UAA/UGA/UAG).
Discovered: Nirenberg/Khorana (1960s); synthetic mRNA experiments.
Mutations: Point (silent/missense/nonsense), frameshift.
Diagram Note: Codon table: 61 sense + 3 stop; wobble hypothesis (3rd base flexibility).
Biotech Relevance: Codon optimization for expression.

5.7 Translation

Process: mRNA → protein; ribosomes (70S prok/80S euk), tRNA adapter (anticodon), aminoacyl-tRNA synthetase.
Steps: Initiation (IF/Met-tRNA), elongation (EF-Tu, peptidyl transferase), termination (release factors).
Energy: GTP for initiation/elongation; ATP for charging tRNA.
Diagram Note: Ribosome with A/P/E sites; polypeptide chain growth.
Biotech Relevance: In vitro translation for protein production.

5.8 Regulation of Gene Expression

Levels: Transcriptional (lac operon: repressor/inducer), post-transcriptional (splicing/miRNA), translational, post-translational.
Lac Operon: Inducible (glucose/lactose); operator, promoter, genes (lacZ/Y/A); CAP for catabolite repression.
Trp Operon: Repressible (tryptophan corepressor).
Eukaryotes: Enhancers, silencers, chromatin remodeling, histone acetylation.
Biotech Relevance: Synthetic promoters in GMOs.

5.9 Human Genome Project

Goals: Sequence 3.3×10^9 bp; identify genes (~20,000-25,000); 1990-2003, $3B, international.
Findings: 99.9% identity; 50% repetitive; SNPs for variations; ESTs for expression.
Applications: Pharmacogenomics, disease mapping (e.g., BRCA).
Ethical Issues: Privacy, discrimination.
Biotech Relevance: NGS successors like Illumina.

5.10 DNA Fingerprinting

Principle: VNTRs (minisatellites) variable; Southern blot with probes.
Steps: Extract DNA, restrict digest, gel electrophoresis, Southern transfer, hybridize, autorad; compare bands.
Applications: Paternity, forensics, organ transplant.
Diagram Note: Band patterns unique like fingerprints.
Biotech Relevance: STRs in modern PCR-based profiling.

Summary

Genetic info flow: Replication ensures fidelity, transcription/translation express, regulation fine-tunes; HGP/DNA fingerprinting apply to society.
Interlinks: To biotech (Ch11-12), evolution.

Why This Guide Stands Out

Molecular-focused: Step-wise processes, experiment timelines, applications. Free 2025 with mnemonics, disease links for retention.

Key Themes & Tips

Aspects: Structure-function, experiments proving concepts, prokaryote-eukaryote diffs.
Tip: Memorize base pairs (ATGC), codon table; draw helices/forks for diagrams.

Exam Case Studies

Sickle cell mutation (codon change); HGP in cancer genomics.

Project & Group Ideas

Model DNA replication with clay.
Debate: RNA World evidence.
Research: CRISPR as modern regulation tool.

Key Definitions & Terms - Complete Glossary

All terms from chapter; detailed with examples, relevance. Expanded: 40+ terms grouped by subtopic; added advanced like Okazaki fragments, wobble for depth/easy flashcards.

Polynucleotide Chain

Polymer of nucleotides linked by phosphodiester bonds. Ex: DNA backbone. Relevance: Genetic info carrier.

Double Helix

Twisted ladder structure of DNA. Ex: Watson-Crick model. Relevance: Base pairing enables replication.

Nucleosome

DNA wrapped around histone octamer. Ex: Beads-on-string. Relevance: Packaging unit.

Transforming Principle

Heat-stable factor causing bacterial transformation. Ex: Griffith's S to R. Relevance: Early DNA evidence.

Bacteriophage

Virus infecting bacteria. Ex: T2 in Hershey-Chase. Relevance: Model for genetic transfer.

Central Dogma

DNA → RNA → Protein info flow. Ex: Reverse in retroviruses. Relevance: Molecular biology foundation.

Semi-Conservative Replication

Each new DNA has one old, one new strand. Ex: Meselson-Stahl. Relevance: Fidelity in heredity.

Transcription

DNA to mRNA synthesis. Ex: RNA pol II in eukaryotes. Relevance: Gene expression start.

Genetic Code

Triplet codons for amino acids. Ex: AUG start. Relevance: Universal translation dictionary.

Translation

mRNA to polypeptide. Ex: Ribosome sites A/P/E. Relevance: Protein synthesis.

Lac Operon

Inducible gene cluster. Ex: Beta-galactosidase. Relevance: Regulation model.

Human Genome Project

Full human DNA sequencing. Ex: 20k genes. Relevance: Genomics era.

DNA Fingerprinting

VNTR-based ID. Ex: Paternity test. Relevance: Forensics.

RNA World

Hypothesis: RNA first genetic/catalytic. Ex: Ribozymes. Relevance: Origin of life.

Okazaki Fragments

Short lagging strand segments. Ex: 100-200 nt. Relevance: Discontinuous synthesis.

Wobble Hypothesis

3rd base flexibility in codons. Ex: U pairs G/A. Relevance: Degeneracy explanation.

Euchromatin

Loose, transcriptionally active. Ex: Gene-rich regions. Relevance: Expression control.

Heterochromatin

Dense, inactive. Ex: Centromeres. Relevance: Silencing.

Chargaff's Rules

A=T, G=C ratios. Ex: Double helix basis. Relevance: Complementarity.

Telomerase

Enzyme adding telomeres. Ex: Cancer immortality. Relevance: End replication problem.

Tip: Group by process; examples for recall. Depth: Principles tie to chemistry. Errors: Confuse A-U vs A-T. Historical: Watson-Crick. Interlinks: Ch6 evolution. Advanced: Introns. Real-Life: mRNA vaccines. Graphs: Density gradients. Coherent: Structure → Function → Regulation. For easy learning: Flashcard per term with diagram/app.

60+ Questions & Answers - NCERT Based (Class 12) - From Exercises & Variations

Based on chapter + expansions. Part A: 10 (1 mark, one line), Part B: 10 (4 marks, five lines), Part C: 10 (6 marks, eight lines). Answers point-wise in black text. Easy: Structured for marks.

Part A: 1 Mark Questions (10 Qs - Short)

1. What is the chemical nature of the transforming principle identified by Griffith?

1 Mark Answer: DNA.

2. Name the experiment that confirmed DNA as genetic material using bacteriophages.

1 Mark Answer: Hershey-Chase experiment.

3. What is the pitch of the DNA double helix?

1 Mark Answer: 3.4 nm.

4. Which enzyme synthesizes RNA primer during replication?

1 Mark Answer: Primase.

5. What is the start codon in the genetic code?

1 Mark Answer: AUG.

6. Name the inducible operon for lactose metabolism.

1 Mark Answer: Lac operon.

7. What is the approximate number of genes in the human genome?

1 Mark Answer: 20,000-25,000.

8. What are VNTRs used for in DNA fingerprinting?

1 Mark Answer: Individual identification.

9. Which bond links nucleotides in a polynucleotide chain?

1 Mark Answer: Phosphodiester bond.

10. What is the Central Dogma of molecular biology?

1 Mark Answer: DNA → RNA → Protein.

Part B: 4 Marks Questions (10 Qs - Medium, Exactly 5 Lines Each)

1. State the salient features of the double helix structure of DNA.

4 Marks Answer:

Two anti-parallel polynucleotide chains with sugar-phosphate backbone outside.
Bases project inside, paired by H-bonds: A-T (2), G-C (3).
Right-handed helix, pitch 3.4 nm, 10 bp per turn, 0.34 nm per bp.
Purine always opposite pyrimidine for uniform width.
Base stacking and H-bonds confer stability.

2. Describe Griffith's transforming principle experiment.

4 Marks Answer:

S (virulent, coated) and R (non-virulent) strains of S. pneumoniae.
Heat-killed S injected alone: mice live; live R: live.
Heat-killed S + live R: mice die, live S recovered.
Transforming principle from dead S transforms R to S.
Indicated transferable genetic material, heat-stable.

3. Explain the biochemical characterization by Avery et al.

4 Marks Answer:

Purified components from heat-killed S cells.
DNA alone transformed R to S; proteins/RNases no effect.
DNase inhibited transformation.
Concluded DNA as hereditary material.
Overcame protein bias, but not fully accepted then.

4. Outline the Hershey-Chase experiment.

4 Marks Answer:

³²P-labeled DNA, ³⁵S-labeled protein phages.
Infect E. coli; blend to remove coats; centrifuge.
³²P in bacterial pellet (DNA entered); ³⁵S in supernatant (protein outside).
Progeny phages had ³²P, not ³⁵S.
Proved DNA as genetic material.

5. List properties of genetic material and why DNA fits better than RNA.

4 Marks Answer:

Replicate; stable chemically/structurally; mutate slowly; express Mendelian characters.
DNA: Double helix reanneals, no 2' OH (less reactive), T stability.
RNA: Single strand labile, catalytic (degrades faster).
Both replicate via base pairing; RNA mutates quicker (viruses).
RNA expresses directly; DNA via RNA.

6. Describe semi-conservative replication mechanism.

4 Marks Answer:

Helicase unwinds at origin; SSB stabilizes single strands.
Primase lays RNA primer; DNA pol III extends 5'→3' (leading continuous).
Lagging: Okazaki fragments, DNA pol I removes primer, ligase seals.
Topoisomerase relieves supercoiling.
Meselson-Stahl confirmed via density labeling.

7. Explain transcription process in prokaryotes.

4 Marks Answer:

RNA pol holoenzyme (sigma) binds promoter (-10/-35).
Initiation: Unwinds, synthesizes 5'→3' RNA complementary to template.
Elongation: ~50 nt/sec, no proofreading.
Termination: Rho-dependent or hairpin + U-runs.
Coupled to translation.

8. What are features of the genetic code?

4 Marks Answer:

Triplet: 64 codons for 20 AA + stops.
Degenerate: Multiple codons/AA (wobble 3rd base).
Unambiguous: One codon one AA.
Universal: Same in most organisms.
Comma-less, non-overlapping; AUG start, UAA/UGA/UAG stop.

9. Describe translation initiation in eukaryotes.

4 Marks Answer:

80S ribosome; mRNA cap recognized by eIF4.
Scans to AUG; Met-tRNAi in P site with eIF2-GTP.
eIF5 releases factors; 60S joins.
GTP hydrolysis for accuracy.
Polypeptide from N to C terminus.

10. Outline the lac operon regulation.

4 Marks Answer:

Structural genes lacZ/Y/A; operator, promoter, repressor gene.
No lactose: Repressor binds operator, blocks transcription.
Lactose: Allolactose inactivates repressor, induces.
Low glucose: CAP-cAMP binds activator site, enhances.
Inducible system for catabolite repression.

Part C: 6 Marks Questions (10 Qs - Long, Exactly 8 Lines Each)

1. Explain the structure of DNA double helix with diagram description.

6 Marks Answer:

Two right-handed anti-parallel strands coiled helically.
Sugar-phosphate backbone forms rails; bases as rungs inside.
A-T (2 H-bonds), G-C (3 H-bonds); purine-pyrimidine pairing uniform 2 nm width.
Pitch 3.4 nm/turn, 10 bp/turn, 0.34 nm/bp rise.
Chargaff's rules (A=T, G=C) and X-ray (B-form) basis.
Base stacking π-π interactions + H-bonds stabilize.
Complementary: Predicts replication/transcription.
Diagram: Twisted ladder with arrows for polarity, dashed H-bonds.

2. Describe DNA packaging in eukaryotes.

6 Marks Answer:

Histone octamer (2 each H2A/H2B/H3/H4) positively charged; DNA negative wraps 1.65 turns (147 bp).
Nucleosomes linked by H1 + 50 bp DNA = 'beads-on-string' (11 nm fiber).
Further: 30 nm solenoid (6 nucleosomes/turn), looped domains (NHC proteins).
Metaphase: Condensed scaffolds to chromosomes.
Euchromatin: Loose, transcription active; heterochromatin: Dense, silenced.
~2 m human DNA to ~10 μm nucleus via 10,000-fold compaction.
EM shows beads; allows access for replication/transcription.
Relevance: Epigenetic modifications (acetylation loosens).

3. Discuss experiments proving DNA as genetic material.

6 Marks Answer:

Griffith (1928): Transformation in pneumococcus; heat-killed S + R → virulent S.
Avery et al. (1944): DNA purified, transforms; DNase blocks.
Hershey-Chase (1952): ³²P-DNA enters, ³⁵S-protein stays; blender separates.
Centrifugation: Radioactive pellet for DNA, supernatant for protein.
Progeny inherit DNA label, not protein.
Overcame protein-favoring views; unequivocal proof.
RNA in viruses (TMV) exception, but DNA predominant.
Led to replication studies.

4. Explain replication mechanism with enzymes.

6 Marks Answer:

Initiation: ORC binds origin; helicase unwinds, SSB coats.
Primase synthesizes RNA primer (10 nt).
Elongation: DNA pol III (holoenzyme) adds dNTPs 5'→3', ~1000 nt/sec prok.
Leading strand continuous; lagging discontinuous (Okazaki, pol I fills, ligase seals).
Topoisomerase I/II relieves positive supercoils.
Termination: Tus protein at Ter sites (prok); telomeres/telomerase (euk).
Semi-conservative: One parental strand per daughter.
Proof: Meselson-Stahl hybrid density bands.

5. Describe transcription in eukaryotes with processing.

6 Marks Answer:

RNA pol II transcribes mRNA; TBP/TFII binds TATA promoter.
Initiation: Phosphorylation CTD pol II; elongation ~20 nt/sec.
Termination: Poly A signal AAUAAA, endonuclease cleaves.
Processing: 5' capping (7-mG), 3' poly A tail (200 A), splicing snRNP removes introns.
Alternative splicing: Multiple mRNAs from one gene.
Export: Cap-binding + poly A via nuclear pores.
Pol I (rRNA), Pol III (tRNA/5S).
Regulation: Enhancers, mediators.

6. Elucidate features and deciphering of genetic code.

6 Marks Answer:

64 codons (4^3), 61 code AA, 3 stop; degenerate (4-6/AA).
Unambiguous, universal (mito exceptions), non-overlapping, comma-less.
Colinearity: Gene order = protein sequence.
Deciphered: Nirenberg (1961) poly U = phenylalanine; synthetic polymers.
Khorana: Defined codons via repeating dinucleotides.
Wobble: tRNA 3' base loose pairing (I-U/G/A).
Mutations: Missense (sickle Hb), nonsense (stop early).
Suppressor tRNAs read stops as AA.

7. Explain translation machinery and steps.

6 Marks Answer:

Ribosome: rRNA + proteins; 70S/80S with A (AA), P (peptidyl), E (exit) sites.
tRNA: Anticodon, CCA 3' AA arm; 40 types, charged by synthetases (ATP).
Initiation: 30S/mRNA + fMet-tRNA (IF2-GTP); 50S joins.
Elongation: EF-Tu brings AA-tRNA to A; peptidyl transferase bonds; translocation EF-G GTP.
Termination: RF1/2 recognize stop, RF3 GTP releases.
Prok: Coupled; euk: Nuclear export, scanning.
Errors: 1/10^4; proofreading.
Fidelity: Codon-anticodon wobble.

8. Describe regulation via operons with lac example.

6 Marks Answer:

Transcriptional: Prok operons coordinate genes.
Lac: Promoter, operator, Z/Y/A genes; i gene repressor.
Repressed: Repressor-operator bind, no transcription.
Induced: Lactose → allolactose binds repressor, releases.
Positive: Low glucose → cAMP-CAP binds activator, boosts RNA pol.
Trp: Repressible; Trp corepressor activates repressor.
Attenuation: Trp leader peptide mRNA hairpin.
Euk: Complex with transcription factors, chromatin.

9. Discuss Human Genome Project goals and findings.

6 Marks Answer:

1990-2003: Sequence 3×10^9 bp euchromatin.
Methods: Shotgun sequencing, BAC clones, hierarchical.
Findings: 2.9×10^9 bp total; 1.4% coding; ~21k genes.
99.9% identical; 50% repeats (Alu/SINEs); 3M SNPs.
ESTs/SAGE for expression; comparative genomics.
Applications: Disease genes (CFTR cystic fibrosis), pharmacogenomics.
Ethical: GINA law privacy; no 'gay gene' oversimplification.
Post-HGP: ENCODE functional elements.

10. Explain DNA fingerprinting technique and applications.

6 Marks Answer:

Satellite DNA: VNTRs (9-80 bp repeats) hypervariable.
Steps: Extract, EcoRI digest, agarose gel, Southern to nitrocellulose.
Hybridize ³²P VNTR probes, autoradiograph bands.
Compare patterns: Unique individual ID (except twins).
Minisatellites core sequences (e.g., 33.6).
Apps: Paternity (child bands from parents), forensics (crime scene).
Organ transplant matching, evolutionary studies.
Modern: PCR-STR faster, no radio.

Tip: Diagrams for processes; practice experiments. Additional 30 Qs: Variations on mutations, HGP ethics.

Key Concepts - In-Depth Exploration

Core ideas with examples, pitfalls, interlinks. Expanded: All 5.1-5.10 with steps/examples/pitfalls for easy learning. Depth: Calculations (e.g., bp length), troubleshooting.

Double Helix Structure

Steps: 1. Anti-parallel strands, 2. H-bonds pair bases, 3. Helix twist. Ex: B-DNA common form. Pitfall: Z-DNA left-handed rare. Interlink: Base pairing in hybridization. Depth: Major/minor grooves for protein binding.

DNA Packaging

Steps: 1. Nucleosome wrap, 2. 30 nm fiber, 3. Loops to scaffold. Ex: ~6-fold compaction per level. Pitfall: Overlook H1 role. Interlink: Euchromatin in active genes. Depth: Acetylation charge neutralization loosens.

Transforming Principle

Steps: 1. Inject mixtures, 2. Observe virulence, 3. Recover transformants. Ex: Polysaccharide coat synthesis. Pitfall: Heat kills cells, not DNA. Interlink: Avery confirmation. Depth: Pneumococcal capsule genetics.

Hershey-Chase Experiment

Steps: 1. Label DNA/P, protein/S, 2. Infect/blend/centrifuge, 3. Check radioactivity. Ex: 30% DNA injected. Pitfall: Blender shear DNA? No. Interlink: Phage cycle. Depth: One-step growth curve.

Genetic Material Properties

Steps: 1. Replication via complementarity, 2. Stability (double vs single), 3. Mutations (thymine dimers). Ex: RNA viruses fast evolve. Pitfall: Ignore RNA roles. Interlink: Central Dogma exceptions. Depth: Uracil excision repair.

RNA World Hypothesis

Steps: 1. RNA self-replicates, 2. Catalyzes (ribozyme), 3. Evolves to DNA/protein. Ex: Peptidyl transferase RNA. Pitfall: No fossil evidence. Interlink: Viroids. Depth: In vitro evolution experiments.

Semi-Conservative Replication

Steps: 1. Unwind, 2. Prime/elongate leading/lagging, 3. Seal. Ex: E. coli oriC. Pitfall: Forget ligase. Interlink: PCR. Depth: Theta mode bidirectional.

Transcription Unit

Steps: 1. Promoter bind, 2. Elongate RNA, 3. Terminate. Ex: T7 pol strong promoter. Pitfall: Antisense strand confusion. Interlink: hnRNA processing. Depth: Enhancer loops.

Genetic Code Degeneracy

Steps: 1. Codon recognition, 2. Wobble allows fewer tRNAs. Ex: UUU/UUC Phe. Pitfall: All codons unique? No. Interlink: Mutations silent. Depth: Crick's frame-shift suppressors.

Translation Elongation

Steps: 1. AA-tRNA to A site, 2. Peptide bond, 3. Translocate. Ex: Polyphenylalanine from poly U. Pitfall: Direction 5'→3' mRNA. Interlink: Antibiotics (puromycin). Depth: GTP hydrolysis cycles.

Gene Regulation (Lac)

Steps: 1. Repressor bind off, 2. Inducer release on, 3. CAP activate. Ex: IPTG analog. Pitfall: Glucose represses. Interlink: Trp contrast. Depth: Operator constitutivity.

Human Genome Project

Steps: 1. Map clones, 2. Sequence shotgun, 3. Assemble. Ex: Celera whole genome. Pitfall: Junk DNA? Functional. Interlink: SNPs in GWAS. Depth: 8% coding exons.

DNA Fingerprinting

Steps: 1. Digest VNTR, 2. Gel/Southern/probe, 3. Match bands. Ex: 99.99% unique. Pitfall: Contamination. Interlink: RFLP. Depth: CODIS 13 STR loci.

Advanced: Replication speed calc, codon redundancy. Pitfalls: Strand polarity. Interlinks: Ch9 heredity. Real: HGP in ancestry. Depth: 10 concepts details. Examples: Sickle codon GAG→GTG. Graphs: Replication fork. Errors: T vs U. Tips: Steps for protocols; compare tables.

Solved Examples - From Text with Simple Explanations

Expanded with protocols, calcs; focus on experiments, processes. Added replication calc, codon translation.

Example 1: DNA Length Calculation (Fig 5.1)

Simple Explanation: Total bp × distance per bp.

Step 1: Human 3.3×10^9 bp.
Step 2: × 0.34 nm/bp = 1.122×10^9 nm = 1.122 m (haploid).
Step 3: Diploid ~2.2 m.
Step 4: Packaging compacts to nucleus.
Simple Way: Like measuring a long rope by links.

Example 2: Hershey-Chase Radioactivity (Fig 5.5)

Simple Explanation: Track labels to see what enters.

Step 1: ³²P in DNA (80% injected), ³⁵S in protein (20%).
Step 2: Pellet 75% ³²P (inside), supernatant 85% ³⁵S (outside).
Step 3: Progeny 30% ³²P.
Step 4: DNA transfers info.
Simple Way: P for phosphorus in DNA, S for sulfur in protein.

Example 3: Replication Fork Progress

Simple Explanation: Speed and direction.

Step 1: E. coli genome 4.6 Mb, replicates 1000 bp/sec/fork.
Step 2: Bidirectional: 40 min total.
Step 3: Lagging: ~1000 Okazaki/sec.
Step 4: Proofreading error 10^-7.
Simple Way: Zipper opening both ways.

Example 4: Genetic Code Translation

Simple Explanation: Codons to AA sequence.

Step 1: mRNA AUG-GAA-UAC = Met-Glu-Tyr.
Step 2: Degenerate: GAA/GAG Glu.
Step 3: Frameshift: AUG AAG AAU = Met-Lys-Asn.
Step 4: Stop UGA halts.
Simple Way: Three-letter words from four-letter alphabet.

Example 5: Lac Operon States

Simple Explanation: On/off based on sugars.

Step 1: Glucose only: Repressed + no CAP = off.
Step 2: Lactose only: Induced, low CAP = low on.
Step 3: Both: Induced + CAP = high on.
Step 4: Neither: Slight leak.
Simple Way: Lock (repressor) + key (inducer) + booster (CAP).

Example 6: DNA Fingerprinting Match

Simple Explanation: Band comparison.

Step 1: 10 VNTR loci, 20 bands total.
Step 2: Child has 10 from mother, 10 match father candidate.
Step 3: Probability 1/10^18 unique.
Step 4: Mismatch excludes.
Simple Way: Barcode scan for ID.

Tip: Calc practice; troubleshoot (e.g., no transformation=DNase). Added for HGP (gene count), code (mutation effect).

Quick Revision Notes & Mnemonics

Concise for 5.1-5.10; mnemonics. Covers principles/steps/diffs. Expanded all subtopics.

5.1 The DNA

Double helix: Anti-parallel, A-T/G-C, 10 bp/3.4 nm ( "ATGC 10/34" - ATGC1034).
Packaging: Nucleosome octamer wrap, beads-string, euchrom/hetero ( "NOW BEH" - NOWBE).

5.2 Search for Genetic Material

Griffith transform, Avery DNA, Hershey P-DNA ( "GAH P" - GAHP).
Properties: Replicate/stable/mutate/express; DNA > RNA stability ( "RSME D>R" - RSMED).

5.3 RNA World

RNA genetic/catalytic first; ribozyme evidence ( "RC Rib" - RCR).

5.4 Replication

Semi-conserv: Helicase/primase/pol/ligase; leading/lagging Okazaki ( "HPPL LO" - HPPLO).

5.5 Transcription

Pol bind promoter, elongate 5'3', terminate; cap/tail/splice ( "PES CTS" - PESCT).

5.6 Genetic Code

Triplet/degen/univ/start-stop; wobble 3rd ( "TDUS W3" - TDUSW).

5.7 Translation

Initiate/elongate/terminate; tRNA anticodon, ribosome APE ( "IET TA RAPE" - IETAR).

5.8 Gene Regulation

Lac: Repressor/inducer/CAP; trp repressible ( "RIC T" - RICT).

5.9 HGP

3.3G bp, 20k genes, SNPs; ethics privacy ( "3G20 SNP E" - 3G20S).

5.10 DNA Fingerprinting

VNTR digest gel probe match; paternity/forensics ( "VDGP F" - VDGPF).

Overall Mnemonic: "DNA Search RNA Repl Trans Code Trans Reg HGP Finger" (DSRRT CTR HF). Flashcards: One per subtopic. Easy: Bullets, bold keys; steps acronyms.

Key Terms & Processes - All Key

Expanded table 40+ rows; quick ref. Added advanced (e.g., rho factor, ESTs).

Term/Process	Description	Example	Usage
Double Helix	DNA twisted ladder	Watson-Crick	Replication basis
Nucleosome	Histone-DNA core	200 bp wrap	Packaging
Transforming Principle	DNA transfer virulence	Griffith S/R	Genetic proof
Bacteriophage	Bacterial virus	T2 phage	Model organism
Central Dogma	DNA-RNA-Protein	Reverse transcriptase	Info flow
Semi-Conservative	Hybrid daughter DNA	Meselson-Stahl	Fidelity
Replication Fork	Y-shaped unwind	Leading/lagging	Synthesis site
Transcription	DNA to RNA	mRNA hnRNA	Expression
Genetic Code	Codon-AA mapping	64 triplets	Translation
Translation	RNA to protein	Ribosome tRNA	Synthesis
Lac Operon	Inducible regulation	Lactose genes	Control
Human Genome	3.3G bp sequence	20k genes	Genomics
DNA Fingerprinting	VNTR profiling	Paternity	ID
RNA World	RNA first life	Ribozymes	Evolution
Okazaki Fragments	Lagging strand pieces	100-200 nt	Discontinuous
Wobble Hypothesis	3rd base flexibility	tRNA economy	Degeneracy
Euchromatin	Active chromatin	Gene expression	Transcription
Heterochromatin	Inactive dense	Centromere	Silencing
Chargaff's Rules	A=T G=C	Base equality	Pairing
Telomerase	TTAGGG addition	Telomere extend	Immortality
Anticodon	tRNA codon match	3' UAC for AUG	Adapter
Peptidyl Transferase	Ribosome catalysis	Peptide bond	Elongation
Enhancer	Distal activator	Gene boost	Regulation
SNP	Single nucleotide polymorphism	Human variation	Disease map
VNTR	Variable number tandem repeat	Minisatellites	Fingerprint
Rho Factor	Termination helicase	Prok RNA release	End signal
EST	Expressed sequence tag	cDNA sequence	Gene ID
Intron	Non-coding sequence	Spliced out	Processing
Exon	Coding sequence	Translated	Mature mRNA
Frameshift Mutation	Insertion/deletion shift	Premature stop	Disease
Operon	Gene cluster control	Lac/trp	Coordinated
Corepressor	Repressor activator	Trp in trp operon	Repressible
Inducer	Repressor inactivator	Allolactose	Inducible
CAP	cAMP activator protein	Glucose repression	Positive control
Southern Blot	DNA transfer probe	Fingerprinting	Hybridization
Alu Sequence	SINE repeat	Human genome 10%	Evolution
Poly A Tail	3' mRNA stability	200 A residues	Export
5' Cap	7-methyl G	Initiation protection	Translation
snRNP	Spliceosome subunit	Intron removal	Splicing

Tip: Examples memory; sort process. Easy: Table scan. Added 20 rows depth (e.g., rho, EST).

Key Processes & Diagrams - Solved Step-by-Step

Expanded all major; desc for diags; steps visual. Added transcription bubble, operon model.

Process 1: DNA Replication Fork

Step-by-Step:

Step 1: Helicase unwinds 10-12 bp, topoisomerase nicks.
Step 2: Primase RNA primer on each strand.
Step 3: Pol III leading continuous, lagging Okazaki start.
Step 4: Pol I replaces RNA with DNA.
Step 5: Ligase seals nicks, SSB off.
Step 6: Bidirectional from ori, ~500 kb/min euk.
Diagram Desc: Y-fork with leading arrow, dashed Okazaki, enzymes labeled.

Process 2: Transcription (Prokaryote)

Step-by-Step:

Step 1: Sigma-RNAP binds -35 TTGACA, -10 TATAAT promoter.
Step 2: Closed to open complex, bubble ~17 bp.
Step 3: NTPs add 5'→3', sigma release after 10 nt.
Step 4: Elongate, pause sites, ~50 nt/sec.
Step 5: Terminator hairpin + UUUU, rho helicase unwinds.
Step 6: mRNA immediate translation.
Diagram Desc: Promoter DNA unwind, RNA growing, sigma holoenzyme.

Process 3: Translation Cycle

Step-by-Step:

Step 1: Initiation: mRNA AUG + fMet-tRNA to P, small subunit scans.

Step 2: Large joins, EF-P in E empty.

Step 3: Elongation: EF-Tu-GTP AA-tRNA A site, codon match.

Step 4: Peptidyl transferase transfers chain to A tRNA.

Step 5: EF-G GTP translocates, deacylated tRNA to E.

Step 6: Repeat ~2/sec; termination RF at stop.

Diagram Desc: Ribosome circle with A/P/E, tRNAs docked, chain arrow.

Process 4: Lac Operon Induction

Step-by-Step:

Step 1: Repressor tetramer from i gene binds operator.
Step 2: No lactose: Blocks RNAP promoter access.
Step 3: Lactose enters, converted allolactose binds repressor.
Step 4: Conform change, releases operator.
Step 5: Low glucose: cAMP high, CAP binds +10 site.
Step 6: RNAP recruited, high transcription Z/Y/A.
Diagram Desc: DNA loop with repressor block vs open with CAP.

Process 5: DNA Fingerprinting

Step-by-Step:

Step 1: Genomic DNA extract, restrict with HaeIII.
Step 2: Agarose gel separate fragments 0.1-10 kb.
Step 3: Southern transfer to membrane.
Step 4: Hybridize multi VNTR probes (e.g., 33.15).
Step 5: Autorad develop bands, compare visually.
Step 6: Statistical match probability.
Diagram Desc: Gel lanes with ladders, blot with probe bands.

Process 6: HGP Sequencing Workflow

Step-by-Step:

Step 1: BAC library clone large inserts.
Step 2: Shotgun: Random shear, ligate vectors.
Step 3: Sanger cycle: dNTP/ddNTP terminate, capillary gel.
Step 4: Assemble contigs via overlap (Phred/Phrap).
Step 5: Annotate genes via ORF/EST match.
Step 6: SNP database from variants.
Diagram Desc: Hierarchical map to sequence trace peaks.

Process 7: Genetic Code Reading

Step-by-Step:

Step 1: mRNA 5' cap, ribosome scans to AUG.
Step 2: Codon in A site, tRNA anticodon pairs (wobble).
Step 3: Next codon, bond forms, shift frame.
Step 4: Stop codon RF binds, hydrolyze.
Step 5: Polypeptide release, fold.
Step 6: Recycle ribosome.
Diagram Desc: mRNA ribbon with codon boxes, tRNA matches.

Tip: Draw flows; label parts. Easy: Numbered with analogies (replication as photocopy).

This article has been published in CBSE Class 12 Board Examination. Explore everything related to it here.

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