Introduction

Molecular Basis of Inheritance explains how genetic information is stored, replicated, and expressed in living organisms. NEET often tests DNA/RNA structure, replication, transcription, translation, mutations, and protein synthesis.

Understanding this topic requires knowledge of key formulas, mechanisms, and molecular processes that ensure accurate transmission of hereditary information.

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1. DNA – The Genetic Material

Structure:

• Double-stranded helix → Watson & Crick model

• Sugar-phosphate backbone, nitrogenous bases (A, T, G, C)

• Base pairing → A-T (2 H-bonds), G-C (3 H-bonds)

Key Points:

• DNA carries genetic information

• Complementary base pairing ensures accurate replication

NEET Formula / Fact:

• Chargaff’s rule: A = T, G = C

• DNA replication → Semi-conservative (Meselson & Stahl)

2. RNA – Messenger and Functional Molecule

Types of RNA:

1. mRNA: Carries coding information from DNA → Ribosome

2. tRNA: Brings amino acids → Matches codon via anticodon

3. rRNA: Forms ribosome structure

4. snRNA: RNA splicing in eukaryotes

NEET Tip:

• RNA is single-stranded, contains uracil (U) instead of T

3. DNA Replication

Definition:

• Process of copying DNA before cell division

Key Steps:

1. Initiation → Origin of replication → Helicase unwinds DNA

2. Elongation → DNA polymerase adds nucleotides (5’→3’)

   • Leading strand → Continuous

   • Lagging strand → Okazaki fragments → Ligase joins fragments

3. Termination → Two identical DNA molecules

NEET Formula / Fact:

• Semi-conservative → Each DNA molecule has 1 parental + 1 new strand

4. Transcription (DNA → RNA)

Definition:

• Synthesis of RNA from DNA template

Key Steps:

1. Initiation → RNA polymerase binds promoter

2. Elongation → RNA synthesized complementary to template strand

3. Termination → RNA polymerase reaches terminator

NEET Tip:

• mRNA sequence = Complementary to template strand

• Only one strand of DNA (template strand) is transcribed

5. Translation (RNA → Protein)

Definition:

• Synthesis of protein using mRNA template at ribosome

Key Steps:

1. Initiation → Ribosome binds start codon (AUG)

2. Elongation → tRNA brings amino acids → Peptide bonds formed

3. Termination → Stop codon (UAA, UAG, UGA) → Protein released

NEET Formula:

• Codon → Triplet of mRNA bases → 1 amino acid

• Degenerate code → Multiple codons code same amino acid

NEET Tip:

• Use mRNA codon table to solve MCQs on protein sequence

6. Genetic Code Features

• Triplet codon → 3 nucleotides → 1 amino acid

• Degenerate → Multiple codons for same amino acid

• Universal → Same codons in almost all organisms

• Start codon: AUG (Methionine)

• Stop codons: UAA, UAG, UGA

NEET Tip:

• Memorize start and stop codons for translation questions

7. Regulation of Gene Expression

Prokaryotes:

• Operon concept → Example: Lac operon (Jacob & Monod)

• Gene expression controlled → Repressor, inducer

Eukaryotes:

• Controlled by enhancers, silencers, transcription factors

NEET Tip:

• Gene regulation questions often linked with environmental adaptation

8. Mutation and Repair

Mutation:

• Permanent change in DNA sequence → Source of variation

• Types:

  1. Point mutation → Single base change → Sickle cell anemia

  2. Frameshift mutation → Insertion/deletion → Nonfunctional protein

  3. Chromosomal mutation → Deletion, duplication, inversion, translocation

DNA Repair Mechanisms:

• Mismatch repair

• Base excision repair

• Nucleotide excision repair

NEET Tip:

• Mutation → Can be beneficial, neutral, or harmful

• Repair mechanisms maintain genome integrity

9. Central Dogma of Molecular Biology

Definition:

• Flow of genetic information → DNA → RNA → Protein

• Proposed by Francis Crick

NEET Formula / Memory Aid:

• DNA (Replicated) → Transcription → RNA → Translation → Protein

• Simplified: “Replication → Transcription → Translation”

NEET Tip:

• Central dogma helps answer protein synthesis and genetic disorder questions

10. NEET Important Formulas / Memory Aids

1. DNA Base pairing: A = T, G = C

2. DNA replication: Semi-conservative → 1 old + 1 new strand

3. Codon formula: 3 mRNA bases → 1 amino acid

4. Start codon → AUG (Methionine), Stop codons → UAA, UAG, UGA

5. Mutation types → Point, Frameshift, Chromosomal

Mnemonic for Central Dogma:
“DNA copies, RNA carries, Protein builds”

11. NEET Exam Tips

• Draw DNA double helix, replication fork, transcription & translation diagram

• Practice mRNA codon → amino acid problems

• Remember mutation types and repair mechanisms

• Focus on central dogma & gene expression

Conclusion

Molecular Basis of Inheritance is a high-yield NEET topic. Mastery of DNA/RNA structure, replication, transcription, translation, genetic code, and mutation is essential for scoring in MCQs, diagram-based, and conceptual questions.

With this StudentBro.in guide, students can efficiently revise formulas, processes, and mechanisms, enhancing speed and accuracy during NEET exams.

Remember: Linking DNA → RNA → Protein → Trait is the key to mastering Molecular Basis of Inheritance for NEET.