Complete Summary and Solutions for Basic Processes – NCERT Class XI Biotechnology, Chapter 7 – DNA Structure, Replication, Gene Expression, Translation, Mutations, Exercises

Comprehensive summary and explanation of Chapter 7 'Basic Processes' from the NCERT Class XI Biotechnology textbook, covering the discovery and evidence for DNA as genetic material, gene and genome organization in prokaryotes and eukaryotes, DNA replication mechanisms, transcription, genetic code, translation, regulation of gene expression, types of mutations, DNA repair, and answers to all textbook questions and exercises.

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Categories: NCERT, Class XI, Biotechnology, Chapter 7, DNA, Gene Expression, Replication, Translation, Mutation, Genetic Code, Summary, Questions, Answers

Tags: Basic Processes, Biotechnology, NCERT, Class 11, DNA, Replication, Gene Expression, Transcription, Translation, Genetic Code, Mutation, DNA Repair, Regulation, Chapter 7, Answers, Extra Questions

Basic Processes: Class 11 NCERT Chapter 7 - Ultimate Study Guide, Notes, Questions, Quiz 2025

Full Chapter Summary & Detailed Notes - Basic Processes Class 11 NCERT

Overview & Key Concepts

Chapter Goal: Explore molecular basis of heredity from DNA's role as genetic material to its replication, expression, code, translation, mutations, repair, and regulation. Exam Focus: Experiments (Griffith, Avery, Hershey-Chase), semi-conservative replication, central dogma, triplet code, wobble hypothesis, lac operon. 2025 Updates: Integration with genomics, CRISPR repair, biotech applications in gene therapy. Fun Fact: DNA's double helix was proposed in 1953, solving Chargaff's rules. Core Idea: DNA stores/transmits info via precise processes. Real-World: Vaccines (mRNA translation), cancer (mutation repair failure). Ties: Links to biomolecules (Ch3), principles of inheritance (Ch6). Expanded: All subtopics (7.1-7.9) covered point-wise with diagram descriptions, steps for processes like replication forks.
Wider Scope: From classical experiments confirming DNA to modern regulation; central dogma (DNA→RNA→Protein); exceptions like RNA viruses.
Expanded Content: Detailed experiments, mechanisms (e.g., Okazaki fragments), code degeneracy, operons; biotech relevance in cloning, editing.

Fig. 7.1: Griffith’s transformation experiment (Description)

Four setups: Live R (survives), Live S (dies), Heat-killed S (survives), Heat-killed S + Live R (dies, live S found). Visual: Mice icons, bacterial colonies (smooth/rough).

7.1 DNA as the Genetic Material

Introduction: Traits inherited via genes on chromosomes (DNA+proteins); challenge: Identify genetic material (DNA vs. protein).
Historical Context: Miescher (1869) isolated nuclein (DNA+protein) from pus cells nuclei.
7.1.1 Discovery of the Transforming Principle (Griffith, 1928):
- Streptococcus pneumoniae: Virulent S (smooth, capsulated, kills mice) vs. non-virulent R (rough, no capsule, harmless).
- Experiments: Live S → death; Live R → survival; Heat-killed S → survival; Heat-killed S + Live R → death with live S in blood.
- Conclusion: R transformed to S by 'transforming principle' from dead S (genetic transfer altering makeup).
7.1.2 Biochemical Characterisation (Avery, MacLeod, McCarty, 1944):
- Extract from heat-killed S: Removed lipids/carbs; retained protein, RNA, DNA.
- Treated extracts: Protease (degrades protein) → transformation; RNase (RNA) → transformation; DNase (DNA) → no transformation.
- Conclusion: DNA is transforming principle (genetic material).
7.1.3 Hershey-Chase Experiment (1952):
- T2 bacteriophage (infects E. coli): DNA (32P-labeled) vs. protein coat (35S-labeled).
- Infection: Blended to remove phage parts; centrifuged (bacteria pellet, supernatant debris).
- Results: 32P in pellet (DNA entered); 35S in supernatant (protein outside).
- Conclusion: DNA directs phage reproduction (genetic material).
Further Evidence: Chargaff (A=T, G=C); Wilkins/Franklin X-rays; Watson/Crick model (Ch3) explains info storage.

Fig. 7.2: Confirmation of transforming principle (Description)

Flowchart: Heat-killed S extract → Remove lipids/sugars → Add enzymes (Protease/RNase: Transformation; DNase: No). Visual: Bacterial colonies smooth/rough.

Fig. 7.3: Hershey-Chase experiment (Description)

Two paths: 35S-protein (red capsule, no sulfur in cells post-centrifuge); 32P-DNA (green, phosphorus in cells). Steps: Infection, blending, centrifugation.

7.2 Prokaryotic and Eukaryotic Gene Organisation

Prokaryotes: No nucleus; circular dsDNA in nucleoid; large size accommodated by supercoiling (negative: opposite helix twist).
Supercoiling: Twisting like rubber band coils; proteins (HU histone-like) condense DNA.
Plasmids: Extra small circular DNA loops (non-essential, e.g., antibiotic resistance).
Eukaryotes: Linear dsDNA in nucleus; packaging via histones (basic proteins).
Nucleosomes: DNA (acidic) wraps 1.65 turns around H2A-H2B-H3-H4 octamer (146 bp); linker DNA (H1 histone) connects 'beads-on-string'.
Packaging Levels: 10 nm beads → 30 nm solenoid fibre → 300 nm looped scaffold → 700 nm metaphase chromosome.
Genome Size: Eukaryotes larger/complex (e.g., humans 3 Gb vs. bacteria 4 Mb); much non-coding/unexpressed DNA.
Gene Definition: DNA segment with promoter; transcribes mRNA for translation (universal mechanism).
Eukaryotic Genes: Introns (non-coding) spliced from primary transcript; exons join for mature mRNA (e.g., β-globin).

Fig. 7.4: Supercoiling of DNA in Prokaryote (Description)

Axis with DNA loop → Supercoil (coiled on itself forming superhelix). Visual: Twisted double helix.

Fig. 7.5: Packaging of Eukaryotic Gene (Description)

DNA helix (2 nm) → Beads-on-string (10 nm nucleosome) → 30 nm fibre → 300 nm supercoil → 700 nm metaphase chromosome. Note: One chromosome = one DNA.

Fig. 7.6: Beads on string structure of chromatin (Description)

Electron micrograph: Nucleosomes (beads) on DNA string; each ~200 bp (146 wrapped + linker).

Fig. 7.7: Genome size variations (Description)

Log scale bar graph: Viruses (10^3 bp) to mammals (10^9 bp); plants largest (10^12 bp). Units: Base pairs to Mb.

7.3 DNA Replication

Semi-Conservative Model: Meselson-Stahl (1958): E. coli in 15N → 14N; density gradients show hybrid DNA (one old/one new strand).
Enzymes: Helicase (unwinds), SSB (stabilizes), Topoisomerase (relieves tension), Primase (RNA primer), DNA Pol III (adds nucleotides 5'→3'), Pol I (removes primer), Ligase (joins Okazaki).
Steps: Origin → Bubble/forks → Leading (continuous) vs. Lagging (discontinuous, Okazaki fragments 100-200 nt) → Proofreading (3'→5' exonuclease).
Key Points: Bidirectional; 50 Svedberg units; error rate 10^-9 with repair.

Fig. 7.8: Replication Fork (Description - Inferred)

Helix unwinds at fork; leading strand continuous, lagging with primers/Okazaki; enzymes labeled.

7.4 Gene Expression

Central Dogma: DNA → Transcription → RNA → Translation → Protein (reverse in retroviruses).
Transcription: RNA Pol binds promoter (TATA box); initiation-elongation-termination; prokaryotes single Pol, eukaryotes three (Pol II for mRNA).
Processing (Eukaryotes): 5' cap, poly-A tail, intron splicing (snRNP spliceosome).

7.5 Genetic Code

Triplet Non-Overlapping: 64 codons (4^3) for 20 AA + start (AUG)/stop (UAA/UGA).
Properties: Degenerate (multiple codons/AA), unambiguous, universal (minor exceptions), comma-free.
Wobble Hypothesis: 3rd base flexible (e.g., U pairs G/A).

Fig. 7.9: Genetic Code Table (Description - Inferred)

64-box table: Codons to AA; AUG Met/start, stops marked.

7.6 Translation

Ribosome: 70S prokaryote (30S+50S); tRNA anticodon matches codon.
Steps: Initiation (AUG + Met-tRNA + factors), Elongation (AA addition, translocation), Termination (release factors).
Energy: GTP/ATP; polyribosomes for efficiency.

Fig. 7.10: Translation Cycle (Description - Inferred)

Ribosome sites (A/P/E); tRNA entry, peptide bond, shift.

7.7 Gene Mutation

Types: Point (substitution/insertion/deletion), frameshift, transversion/transition.
Effects: Missense (AA change), nonsense (premature stop), silent (synonymous).
Causes: Spontaneous (tautomerism), induced (UV, chemicals).

7.8 DNA Repair

Mechanisms: Photoreactivation (light enzyme), Excision (nucleotide/base, NER/BER), Mismatch (post-replication), Recombination.
Key: Proofreading during replication; xeroderma pigmentosum (NER defect).

7.9 Regulation of Gene Expression

Prokaryotes: Lac operon (inducible: lactose induces, repressor binds operator; CAP activator).
Eukaryotes: Enhancers/silencers, chromatin remodeling, miRNA, transcription factors.
Levels: Transcriptional, post-transcriptional, translational, post-translational.

Fig. 7.11: Lac Operon (Description - Inferred)

Promoter-operator-lacZYA; repressor/allolactose binding; glucose low → CAP activation.

Summary

DNA central to heredity; processes ensure fidelity/variation; regulation fine-tunes expression for adaptation.
Interlinks: To Ch6 inheritance, Ch8 applications.

Why This Guide Stands Out

Process-focused: Step-wise mechanisms, experiment timelines, visuals. Free 2025 with mnemonics, biotech links for retention.

Key Themes & Tips

Aspects: Fidelity (repair), economy (regulation), universality (code).
Tip: Mnemonic for code: "64 codons, 61 sense, 3 stop" (6353); practice replication forks.

Exam Case Studies

Sickle cell (mutation), gene therapy (regulation).

Project & Group Ideas

Model replication with beads.
Debate: Code universality exceptions.
Research: CRISPR repair.

Key Definitions & Terms - Complete Glossary

All terms from chapter; detailed with examples, relevance. Expanded: 40+ terms with depth; grouped by subtopic. Added replication/regulation terms.

Transforming Principle

Genetic material from dead S bacteria transforming R. Relevance: Griffith's discovery. Ex: DNA in pneumonia vaccine. Depth: Avery confirmed.

Semi-Conservative Replication

Each new DNA has one old/one new strand. Relevance: Meselson-Stahl. Ex: Hybrid density. Depth: Ensures fidelity.

Nucleosome

DNA wrapped around histone octamer. Relevance: Packaging. Ex: Beads-on-string. Depth: 146 bp wrapped.

Okazaki Fragments

Short lagging strand segments. Relevance: Discontinuous synthesis. Ex: 100-200 nt. Depth: Primase/Pol I/Ligase.

Central Dogma

DNA→RNA→Protein info flow. Relevance: Gene expression. Ex: Transcription/translation. Depth: Reverse in retroviruses.

Genetic Code

Triplet codons for AA. Relevance: Translation. Ex: AUG start/Met. Depth: Degenerate, wobble.

Operon

Gene cluster with regulation. Relevance: Prokaryote control. Ex: Lac (inducible). Depth: Promoter/operator.

Intron

Non-coding spliced sequence. Relevance: Eukaryote processing. Ex: β-globin. Depth: Spliceosome.

Mutation

DNA sequence change. Relevance: Variation/disease. Ex: Sickle cell point. Depth: Frameshift vs. substitution.

Excision Repair

Removes damaged nucleotide. Relevance: DNA maintenance. Ex: NER for UV. Depth: UvrABC enzymes.

Supercoiling

DNA twisting for compaction. Relevance: Prokaryote packaging. Ex: Negative in bacteria. Depth: Topoisomerase relieves.

Anticodon

tRNA loop matching codon. Relevance: Translation. Ex: UAC for AUG. Depth: Wobble at 3rd base.

Promoter

RNA Pol binding site. Relevance: Transcription initiation. Ex: TATA box. Depth: -10/-35 in prokaryotes.

Degeneracy

Multiple codons per AA. Relevance: Error buffer. Ex: 4 for Ala. Depth: 3rd base variation.

Poly-A Tail

3' mRNA addition for stability. Relevance: Eukaryote processing. Ex: 200 A. Depth: Export/degradation control.

Helicase

Unwinds DNA at fork. Relevance: Replication. Ex: 5'→3' direction. Depth: ATP-dependent.

Ribosome

Protein synthesis site. Relevance: Translation. Ex: 70S/80S. Depth: A/P/E sites.

Frameshift Mutation

Insertion/deletion shifts reading. Relevance: Severe change. Ex: Tay-Sachs. Depth: All downstream altered.

Photoreactivation

Light repairs UV dimers. Relevance: Direct reversal. Ex: Photolyase enzyme. Depth: Bacteria/plants.

Repressor

Binds operator to block transcription. Relevance: Negative control. Ex: Lac repressor. Depth: Allolactose inducer.

Enhancer

Distant activator sequence. Relevance: Eukaryote regulation. Ex: Tissue-specific. Depth: Loops to promoter.

Primer

Short RNA for Pol start. Relevance: Replication. Ex: Primase synthesizes. Depth: 5'-3' only.

Stop Codon

UAA/UGA/UAG; no tRNA. Relevance: Termination. Ex: Release factors bind. Depth: Non-degenerate.

Mismatch Repair

Fixes replication errors. Relevance: Post-repl. Ex: MutS recognizes. Depth: Methyl-directed in E. coli.

Histone Octamer

H2A/2B/3/4 core for nucleosome. Relevance: Packaging. Ex: Acidic DNA wraps. Depth: + charge binds phosphate.

Plasmid

Extra circular DNA. Relevance: Prokaryote accessory. Ex: Antibiotic resistance. Depth: Replicates independently.

Spliceosome

Removes introns. Relevance: mRNA processing. Ex: snRNPs U1-U6. Depth: Lariat intermediate.

Wobble Hypothesis

3rd base loose pairing. Relevance: Fewer tRNAs. Ex: I pairs U/C/A. Depth: Crick's proposal.

Chargin

AA-tRNA synthetase specificity. Relevance: Code fidelity. Ex: 20 enzymes. Depth: Proofreads.

Transversion

Purine↔pyrimidine change. Relevance: Mutation type. Ex: A→C. Depth: More disruptive than transition.

Inducer

Removes repressor. Relevance: Operon activation. Ex: Lactose in lac. Depth: Allolactose analog.

5' Cap

7-methyl G for mRNA stability. Relevance: Eukaryote. Ex: Translation initiation. Depth: E1 enzyme.

Tip: Group by process (replication/expression); examples link experiments. Depth: Enzymes tie mechanisms. Errors: Confuse semi-conservative/dispersive. Historical: Hershey 1952. Interlinks: Ch6 genes. Advanced: Code evolution. Real-Life: mRNA vaccines. Graphs: Code wheel. Coherent: Experiments → Mechanisms → Regulation. For easy learning: Flashcard per term with enzyme/example.

60+ Questions & Answers - NCERT Based (Class 11) - From Exercises & Variations

Based on chapter content + expansions. Part A: 10 (1 mark short, one line each), Part B: 10 (4 marks medium, five lines each), Part C: 10 (6 marks long, eight lines each). Answers point-wise, step-by-step for marks. Easy learning: Structured, concise. Additional 30 Qs follow similar pattern in full resource.

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

1. Who discovered the transforming principle in bacteria?

1 Mark Answer: Frederick Griffith.

2. What enzyme degrades DNA in Avery's experiment?

1 Mark Answer: Deoxyribonuclease (DNase).

3. In Hershey-Chase, which isotope labels DNA?

1 Mark Answer: Radioactive phosphorus (32P).

4. What is the basic unit of chromatin packaging?

1 Mark Answer: Nucleosome.

5. What is the direction of DNA synthesis?

1 Mark Answer: 5' to 3'.

6. How many codons in genetic code?

1 Mark Answer: 64.

7. What is the start codon?

1 Mark Answer: AUG (methionine).

8. What repairs UV damage directly?

1 Mark Answer: Photoreactivation.

9. What is the lac operon?

1 Mark Answer: Inducible prokaryotic gene cluster.

10. What are introns?

1 Mark Answer: Non-coding sequences spliced out.

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

1. Describe Griffith's transformation experiment.

4 Marks Answer:

Live S bacteria kill mice; live R harmless.
Heat-killed S harmless alone.
Heat-killed S + live R kills, yields live S.
R transformed by principle from S.
Indicates genetic transfer.

2. Explain Avery's biochemical characterisation.

4 Marks Answer:

Extract heat-killed S minus lipids/carbs.
Treat: Protease/RNase allow transformation.
DNase prevents transformation.
DNA is transforming agent.
Confirms Griffith.

3. Outline Hershey-Chase experiment results.

4 Marks Answer:

32P-DNA enters bacteria (pellet radioactive).
35S-protein stays outside (supernatant).
Phage multiplies inside via DNA.
Protein not genetic material.
Supports DNA role.

4. Describe prokaryotic DNA packaging.

4 Marks Answer:

Circular dsDNA in nucleoid.
Supercoiling (negative) compacts.
HU proteins aid condensation.
Plasmids extra loops.
Accommodates large size.

5. Explain eukaryotic nucleosome structure.

4 Marks Answer:

Histone octamer (2 each H2A/B/3/4).
DNA wraps 146 bp.
H1 on linker DNA.
Beads-on-string chromatin.
Further coils to chromosome.

6. What is semi-conservative replication?

4 Marks Answer:

One old/one new strand per duplex.
Meselson-Stahl: 15N-14N hybrid.
Enzymes: Helicase, Pol III.
Leading continuous, lagging fragments.
Proofreading fidelity.

7. Describe genetic code properties.

4 Marks Answer:

Triplet: 64 codons.
Degenerate: Multiple per AA.
Unambiguous: One codon one AA.
Universal: All organisms.
Comma-free: No spacers.

8. Outline translation steps.

4 Marks Answer:

Initiation: AUG, Met-tRNA, factors.
Elongation: Codon-anticodon, peptide bond.
Translocation: Ribosome shifts.
Termination: Stop codon, release.
GTP energy.

9. What are types of gene mutations?

4 Marks Answer:

Point: Base substitution.
Frameshift: Indel shifts reading.
Missense: AA change.
Nonsense: Early stop.
Silent: No effect.

10. Explain lac operon regulation.

4 Marks Answer:

Repressor binds operator without lactose.
Allolactose induces, releases repressor.
Low glucose: CAP activates promoter.
Genes lacZ/Y/A expressed.
Inducible system.

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

1. Describe Griffith's and Avery's experiments on transforming principle.

6 Marks Answer:

Griffith: S virulent (smooth), R avirulent (rough).
Live S kills mice; heat-killed S + R kills, transforms R to S.
Principle transfers virulence genetically.
Avery: Extract heat-killed S; treat enzymes.
Protease/RNase: Transformation occurs.
DNase: No transformation.
DNA is genetic material.
Biochemical proof.

2. Explain Hershey-Chase and Meselson-Stahl experiments.

6 Marks Answer:

Hershey-Chase: T2 phage; 32P DNA, 35S protein.
Infection, blend, centrifuge: 32P in bacteria, 35S outside.
DNA enters, directs reproduction.
Meselson-Stahl: E. coli 15N to 14N medium.
Generations: Hybrid density F1, light F2.
Semi-conservative model confirmed.
No dispersive/conservative.
Supports Watson-Crick.

3. Detail prokaryotic vs. eukaryotic gene organisation.

6 Marks Answer:

Prokaryote: Circular DNA nucleoid, supercoiling, HU proteins.
Plasmids accessory; compact for small cells.
Eukaryote: Linear DNA nucleus, histones.
Nucleosomes: Octamer core, linker H1.
Levels: 10 nm beads → 30 nm fibre → 700 nm chromosome.
Genome larger, non-coding introns.
Splicing for mRNA.
Packaging regulates access.

4. Describe DNA replication mechanism with enzymes.

6 Marks Answer:

Initiation: Origin, helicase unwinds, SSB stabilizes.
Primase RNA primer.
Elongation: Pol III adds dNTPs 5'→3'.
Leading continuous; lagging Okazaki fragments.
Pol I removes primer, fills; ligase joins.
Topoisomerase relieves supercoils.
Proofreading 3'→5' exonuclease.
Bidirectional forks.

5. Explain transcription and mRNA processing in eukaryotes.

6 Marks Answer:

RNA Pol II binds promoter (TATA), sigma factor prokaryote.
Initiation: NTPs, 5'→3' elongation.
Termination: Poly-A signal.
Processing: 5' cap (stability), poly-A tail (export).
Splicing: Spliceosome removes introns, joins exons.
hnRNA to mature mRNA.
Alternative splicing diversity.
Export via nuclear pores.

6. Discuss genetic code features and wobble hypothesis.

6 Marks Answer:

64 triplets: 61 AA, 3 stop, 1 start.
Degenerate: Redundancy at 3rd base.
Unambiguous/comma-free/universal.
Wobble: 3rd base flexible pairing (G-U, I-A/C/U).
Fewer tRNAs (32 vs. 61).
Crick proposed; explains efficiency.
Exceptions: Mitochondria slight variation.
Deciphered by Nirenberg/Khorana.

7. Outline translation process in detail.

6 Marks Answer:

Initiation: 30S binds mRNA, AUG; fMet-tRNA, IFs, 50S joins (70S).
Elongation: EF-Tu brings AA-tRNA to A site.
Peptide bond (peptidyl transferase), translocation (EF-G, GTP).
Cycle repeats till stop.
Termination: RF1/2 recognize stop, RF3 releases.
Polypeptide folds.
Energy: 2 GTP/AA.
Prokaryote: Coupled to transcription.

8. Explain types and causes of gene mutations.

6 Marks Answer:

Spontaneous: Tautomerism, depurination.
Induced: UV (thymine dimers), chemicals (alkylating), radiation.
Point: Transition (purine-purine), transversion.
Insertion/deletion: Frameshift if not multiple of 3.
Effects: Missense (sickle), nonsense (thalassemia), silent.
Large: Deletions/duplications.
Biotech: Site-directed mutagenesis.
Evolution source.

9. Describe DNA repair mechanisms.

6 Marks Answer:

Direct: Photoreactivation (photolyase splits dimers).
Base excision (BER): Glycosylase removes base, AP endonuclease.
Nucleotide excision (NER): UvrABC excises oligonucleotide.
Mismatch: MutS/H/L, excises error strand.
Double-strand: Homologous recombination, NHEJ.
Proofreading during replication.
Defects: Xeroderma (NER), Lynch syndrome (mismatch).
Maintains genome integrity.

10. Elaborate on lac operon as gene regulation model.

6 Marks Answer:

Structural genes lacZ/Y/A (β-gal/permease/transacetylase).
Promoter: RNA Pol; operator: Repressor binds.
Regulator gene: i (repressor protein).
No lactose: Repressor blocks transcription.
Lactose: Allolactose binds repressor, induces.
Glucose high: No CAP-cAMP activation.
Low glucose: CAP binds, enhances.
Catabolite repression; model for inducible.

Tip: Use diagrams/enzymes for marks; practice code tables. Easy learning: Short for recall, long for essays. Additional 30 Qs: Variations on repair, code exceptions.

Key Concepts - In-Depth Exploration

Core ideas with examples, pitfalls, interlinks. Expanded: All concepts from 7.1-7.9 with steps/examples for easy learning. Added depth with experiment steps, mechanism calculations.

Transforming Principle (7.1)

Genetic transfer altering traits. Steps: 1. Heat-kill donor, 2. Mix recipient, 3. Observe change. Ex: R to S bacteria. Pitfall: Confuse with conjugation. Interlink: Avery biochemical. Depth: DNA uptake; biotech transformation.

Semi-Conservative Replication (7.3)

Hybrid daughter DNA. Steps: 1. Unwind, 2. Template strands, 3. New synthesis, 4. Hybrid forms. Ex: Meselson density shift. Pitfall: Vs. conservative. Interlink: Hershey DNA entry. Depth: Fork speed 50 nt/s; errors 1/10^9.

Nucleosome Packaging (7.2)

Compacts linear DNA. Steps: 1. Octamer assembly, 2. Wrap 1.65 turns, 3. Linker H1, 4. Coil levels. Ex: 2m human DNA to 0.09mm nucleus. Pitfall: Histone types mixup. Interlink: Regulation access. Depth: Acetylation loosens chromatin.

Central Dogma (7.4)

Info flow DNA-RNA-Protein. Steps: 1. Transcription (mRNA), 2. Processing, 3. Translation. Ex: Gene to enzyme. Pitfall: Ignore reverse transcriptase. Interlink: Code translation. Depth: Prions violate (protein only).

Genetic Code Degeneracy (7.5)

Redundancy buffers mutations. Steps: 1. Triplet reading, 2. 3rd base wobble, 3. Synonymous codons. Ex: CCU/CCC Pro. Pitfall: Assume equal codons. Interlink: Wobble efficiency. Depth: 61/64 sense; mitochondrial variations.

Translation Elongation (7.6)

AA chain building. Steps: 1. tRNA to A site, 2. Bond formation, 3. Translocation, 4. Repeat. Ex: Poly-U → poly-Phe. Pitfall: Direction confusion. Interlink: Ribosome sites. Depth: 2 AA/s; GTP hydrolysis.

Point Mutation (7.7)

Single base change. Steps: 1. Base alteration, 2. Transcription/translation error, 3. Phenotype shift. Ex: Sickle hemoglobin GAG→GTG. Pitfall: Vs. chromosomal. Interlink: Repair failure. Depth: Transition more common.

Excision Repair (7.8)

Removes damage. Steps: 1. Recognize lesion, 2. Excise segment, 3. Fill gap (Pol), 4. Ligate. Ex: NER for thymine dimers. Pitfall: Confuse BER/NER. Interlink: Replication proofreading. Depth: XP disease defect.

Lac Operon Induction (7.9)

Gene on/off switch. Steps: 1. Repressor binds operator, 2. Inducer removes, 3. Pol transcribes, 4. CAP boosts if cAMP high. Ex: Lactose metabolism. Pitfall: Glucose repression. Interlink: Eukaryote enhancers. Depth: Negative/positive control.

Intron Splicing (7.4)

Removes non-coding. Steps: 1. U1 binds 5' splice, 2. Lariat 2-3', 3. Exon join, 4. Lariat degrade. Ex: β-globin 1 intron. Pitfall: Prokaryote absence. Interlink: Alternative isoforms. Depth: Self-splicing ribozymes.

Advanced: Replication time: E. coli 40 min. Pitfalls: Code overlapping myth. Interlinks: Ch8 biotech. Real: mRNA vaccines (expression). Depth: 7.1 experiments timelines. Examples: CFTR mutation. Graphs: Density gradients. Errors: Strand direction. Tips: Steps for processes; compare prokary/eukary tables.

Historical Perspectives - Detailed Guide

Timeline of molecular genetics; expanded with points for easy learning; links to key experiments. Added Miescher to operon era.

Early Discoveries (19th C)

1869: Miescher isolates nuclein (DNA) from nuclei.
1880s: Altmann renames nucleic acid.
1900s: Chromosomes as heredity carriers (Sutton).

Depth: Pus cells source; acidic nature.

Transformation Era (1920s-40s)

1928: Griffith pneumonia vaccine, transforming principle.
1944: Avery/McCarty DNA confirmation.
1949: Chargaff base ratios (A=T).

Depth: Biochemical vs. protein hypothesis.

Phage & Model Era (1950s)

1952: Hershey-Chase DNA proof.
1953: Watson-Crick double helix.
1958: Meselson-Stahl semi-conservative.

Depth: Blender experiment; density labeling.

Code & Expression (1960s)

1961: Nirenberg poly-U Phe codon.
1965: Khorana synthetic code.
1961: Jacob-Monod operon model.

Depth: Cell-free translation; lac induction.

Modern Mechanisms (1970s+)

1974: Recombinant DNA (Cohen).
1977: Introns discovery (Berget).
1980s: PCR (Mullis), sequencing.

Depth: Spliceosome; wobble Crick 1966.

Repair & Regulation

1960s: Excision repair (Setlow).
1970s: Mismatch (Modrich).
1980s: Enhancers (Banerji).

Depth: XP linkage; miRNA 1993.

Tip: Link to tools (phage for labeling). Depth: 1953 photo 51 key. Examples: 1944 Avery ignored initially. Graphs: Timeline milestones. Advanced: Human genome 2003. Easy: Chronological bullets with impacts.

Solved Examples - From Text with Simple Explanations

Expanded with more examples, steps for easy understanding; focus on experiments, code, replication. Added semi-conservative, operon calc.

Example 1: Griffith Transformation (Fig 7.1)

Simple Explanation: Dead cells 'teach' live ones virulence.

Step 1: Infect mice with strains.
Step 2: Mix heat-killed virulent + avirulent.
Step 3: Death indicates transformation.
Step 4: Live virulent in blood.
Simple Way: Like copying homework from deceased friend.

Example 2: Hershey-Chase Labeling

Simple Explanation: Tag parts to see what enters.

Step 1: Grow phage with 32P/35S.
Step 2: Infect, blend off coats.
Step 3: Centrifuge: Pellet DNA, supernatant protein.
Step 4: New phages from infected cells.
Simple Way: DNA is the 'brain', protein shell.

Example 3: Semi-Conservative Density

Simple Explanation: Heavy to light shift proves hybrid.

Step 1: 15N bacteria to 14N medium.
Step 2: F1 hybrid band.
Step 3: F2 half hybrid, half light.
Step 4: No heavy band.
Simple Way: Each copy half old recipe.

Example 4: Genetic Code Reading

Simple Explanation: Triplets spell AA words.

Step 1: mRNA AUG-GCA-UUU.
Step 2: Codons Met-Ala-Phe.
Step 3: tRNAs match anticodons.
Step 4: Chain Met-Ala-Phe.
Simple Way: Morse code for proteins.

Example 5: Lac Operon State

Simple Explanation: Switch on for lactose, off for glucose.

Step 1: No lactose: Repressor blocks.
Step 2: Lactose present: Inducer frees.
Step 3: Low glucose: cAMP-CAP boosts.
Step 4: High expression.
Simple Way: Light switch with two controls.

Example 6: Mutation Effect (Sickle Cell)

Simple Explanation: One letter change sickens.

Step 1: Normal GAG (Glu) to GTG (Val).
Step 2: Codon change in β-globin.
Step 3: Sticky hemoglobin aggregates.
Step 4: Red cells sickle, anemia.
Step 5: Heterozygous advantage (malaria).
Simple Way: Typo in blood recipe.

Tip: Draw forks/codes; calculate densities. Added for splicing (exon join), repair (excision patch).

Quick Revision Notes & Mnemonics

Concise notes for all subtopics 7.1-7.9; mnemonics for easy recall. Covers mechanisms, steps, differences. Expanded with all subtopics.

7.1 DNA Genetic Material

Griffith: S/R transform ( "G SRT" - GSRT). Avery: DNAse blocks ( "A D Block" - ADB). Hershey: 32P enters ( "H P Enter" - HPE).
Chargaff A=T.

7.2 Gene Organisation

Prok: Supercoil circular ( "P SC Circ" - PSC). Euk: Nucleosome octamer H1 linker ( "E NO H Link" - ENOHL). Introns splice ( "I Splice" - IS).
Genome: Plants largest.

7.3 DNA Replication

Semi-cons: Hybrid ( "SC Hybrid" - SCH). Enzymes: Hel-Prima-Pol-Lig ( "H P P L" - HPPL). Leading cont, lag Okazaki ( "LCO LagO" - LCLO).
Bidirect forks.

7.4 Gene Expression

Central: DNA-RNA-Prot ( "DRP Flow" - DRPF). Transc: Pol promoter ( "T Pol P" - TPP). Process: Cap-tail-splice ( "CTS" - CTS).
hnRNA mature.

7.5 Genetic Code

64 triplet degene wobble ( "64 TDW" - 64TDW). Start AUG, stop UAA/UGA ( "A Start Stops" - ASS). Universal comma-free.

7.6 Translation

Init-Elong-Term ( "IET Cycle" - IETC). Rib 70S A/P/E ( "R APE" - RAPE). tRNA anticodon ( "t Anti" - tA).
GTP energy.

7.7 Gene Mutation

Point/frame/indel ( "PFI Types" - PFIT). Causes: Spont/induce ( "SI Causes" - SIC). Effects: Miss/nons/silent ( "MNS" - MNS).

7.8 DNA Repair

Photo/exc/mism/recomb ( "PEM R" - PEMR). NER UV dimers ( "N UV D" - NUD). Proofread 3'-5' ( "P 35" - P35).

7.9 Regulation

Lac: Rep-induce-CAP ( "RIC Operon" - RICO). Prok operon, euk enhance ( "POE" - POE). Levels: Trans/post-trans ( "TPT" - TPT).

Overall Mnemonic: "DNA Rep Exp Code Trans Mut Rep Reg" (DRECTMRR). Flashcards: One per subtopic. Easy: Bullets, bold keys; steps for enzymes/codons.

Key Terms & Processes - All Key

Expanded table with 40+ rows; comprehensive for quick reference. Added code/repair terms.

Term/Process	Description	Example	Usage
Transforming Principle	Genetic transfer agent	Griffith bacteria	DNA proof
Nuclein	DNA+protein isolate	Miescher pus	Early discovery
Supercoiling	DNA compaction twist	Bacterial negative	Packaging
Plasmid	Extra DNA loop	Resistance gene	Cloning vector
Histone Octamer	H2A/B/3/4 core	Nucleosome wrap	Euk packaging
Semi-Conservative	Hybrid replication	Meselson hybrid	Model
Okazaki Fragment	Lagging short DNA	100 nt prokary	Discontinuous
Helicase	Unwinds helix	Replication fork	Initiation
Central Dogma	DNA-RNA-Protein	Gene expression	Flow
Promoter	Pol binding site	TATA box	Transcription
Intron	Non-coding spliced	β-globin	Processing
Genetic Code	Triplet AA dict	AUG Met	Translation
Wobble	3rd base flex	G-U pair	Efficiency
Anticodon	tRNA match loop	UAC-AUG	Decoding
Ribosome	Synthesis machine	70S prok	A/P/E sites
Point Mutation	Base change	Sickle GAG-GTG	Variation
Frameshift	Indel shift	Cystic fibrosis	Severe
Photoreactivation	Light dimer split	Photolyase	Direct repair
NER	Nucleotide excision	UV damage	Cut-patch
Operon	Regulated cluster	Lac ZYA	Prok control
Repressor	Operator blocker	Lac i gene	Negative reg
Inducer	Repressor remover	Allolactose	Activation
CAP	cAMP activator	Glucose low	Positive reg
5' Cap	mRNA stability	7-mG	Processing
Poly-A Tail	3' export aid	200 A	Stability
Spliceosome	Intron remover	snRNP U1-6	Splicing
Degeneracy	Code redundancy	4 Ala codons	Buffer
Stop Codon	Termination signal	UAA amber	Release
Primase	RNA primer synth	Lagging start	Replication
Ligase	Joins fragments	Okazaki seal	Finalizing
Topoisomerase	Relieves tension	Swivelase	Supercoil
hnRNA	Heterogeneous nuclear	Primary transcript	Pre-mRNA
Chargin	AA attachment	Synthetase	tRNA load
Mismatch Repair	Error correction	MutS E.coli	Post-repl
Enhancer	Distant activator	Tissue spec	Euk reg
Transversion	Purine-pyrim swap	A to C	Mutation
Tautomerism	Base isomer shift	Mispair cause	Spont mut
snRNP	Splice helper	U1 5' site	Splicing
Peptidyl Transferase	Bond former	Ribozyme	Elongation
Release Factor	Stop recognizer	RF1 UAA	Termination
BER	Base excision	Depurination	Repair
NHEJ	Non-homol end join	DSB fix	Error-prone

Tip: Examples aid memory; sort by section. Easy: Table scan for exams. Added 20 rows for depth (e.g., snRNP, NHEJ).

Key Processes & Diagrams - Solved Step-by-Step

Expanded with all major processes; descriptions for diagrams; steps for visualization. Added transcription, code reading, operon.

Process 1: Transformation (Fig 7.1)

Step-by-Step:

Step 1: Culture S/R strains.
Step 2: Heat-kill S, mix live R.
Step 3: Inject mice, observe death.
Step 4: Culture blood: Live S colonies.
Step 5: Genetic uptake confirmed.
Diagram Desc: Four mouse outcomes with bacteria icons.

Process 2: DNA Replication Fork

Step-by-Step:

Step 1: Origin unwind (helicase).
Step 2: Primers on templates.
Step 3: Leading Pol III continuous.
Step 4: Lagging: Multiple primers, Okazaki.
Step 5: Seal with ligase.
Diagram Desc: Y-fork with leading/lagging arrows, enzymes.

Process 3: Transcription Initiation

Step-by-Step:

Step 1: Pol holoenzyme to promoter.
Step 2: Closed complex, unwind to open.
Step 3: First NTPs, 5'→3' chain.
Step 4: Elongate ~10 nt/s, sigma release.
Step 5: Terminator hairpin stop.
Diagram Desc: Promoter-DNA-Pol bubble, RNA growing.

Process 4: mRNA Splicing

Step-by-Step:

Step 1: U1/U2 bind splice sites.
Step 2: U4/U5/U6 assemble spliceosome.
Step 3: 5' cut, lariat 2'-3' bond.
Step 4: 3' cut, exons ligate.
Step 5: Lariat degraded.
Diagram Desc: Pre-mRNA with intron loop, exon join.

Process 5: Genetic Code Translation

Step-by-Step:

Step 1: Ribosome scans to AUG.
Step 2: tRNA anticodon pairs codon.
Step 3: Next tRNA A site, bond forms.
Step 4: Shift to P/E, repeat.
Step 5: Stop: RF releases chain.
Diagram Desc: mRNA thread through ribosome, tRNAs docked.

Process 6: NER Repair

Step-by-Step:

Step 1: Damage recognition (XPA).
Step 2: Unwind, excise 24-32 nt (XPF/ERCC1).
Step 3: Gap fill by Pol δ/ε.
Step 4: Ligase I seals.
Step 5: TFIIH helicase/kinase.
Diagram Desc: DNA helix with dimer cut out, patch inserted.

Process 7: Lac Operon Activation

Step-by-Step:

Step 1: Repressor i gene product binds operator.
Step 2: Lactose → allolactose binds repressor.
Step 3: Repressor off, Pol to promoter.
Step 4: Glucose low → cAMP high, CAP binds upstream.
Step 5: High transcription lac genes.
Diagram Desc: DNA with repressor/allolactose/CAP labels, on/off states.

Tip: Draw bubbles/forks; label steps. Easy: Numbered steps with analogies (e.g., replication as zipper, splicing as edit).

This article has been published in CBSE Class 11 Annual Assessment. Explore everything related to it here.

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