Unit 4: Nucleic Acid Metabolism & Genetic Information Transfer

February 20, 2026

Semester 2
BP203T

Introduction to Nucleic Acid Metabolism & Genetic Information Transfer

Unit 4 covers ‘The Central Dogma of Molecular Biology’ – the flow of genetic information from DNA to RNA to Protein. It includes the biosynthesis and breakdown of nucleotides (clinically important for Gout), DNA Replication, Transcription, and the entire mechanism of Protein Synthesis (Translation).

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Syllabus & Topics

  • 1Biosynthesis of Purine nucleotides: De novo pathway (key steps and precursors).
  • 2Biosynthesis of Pyrimidine nucleotides: De novo pathway.
  • 3Catabolism of Purine nucleotides: Pathway to Uric Acid.
  • 4Hyperuricemia and Gout: Mechanism, clinical features.
  • 5Organization of Mammalian Genome: Chromatin, Nucleosomes, Histones.
  • 6Structure of DNA (Watson-Crick Double Helix Model) and its functions.
  • 7Structure of RNA (mRNA, rRNA, tRNA) and their functions.
  • 8DNA Replication: Semi-conservative model (Meselson-Stahl experiment), key enzymes.
  • 9Transcription (RNA Synthesis): Mechanism, RNA Polymerase, and promoters.
  • 10Genetic Code: Properties (Triplet, degenerate, universal, non-overlapping).
  • 11Translation (Protein Synthesis): Steps – Initiation, Elongation, Termination.
  • 12Inhibitors of Protein Synthesis (e.g., Puromycin, Linezolid, Chloramphenicol).

Learning Objectives

Explain Gout: Describe the metabolic defect in Gout and the mechanism of action of Allopurinol.
Draw DNA: Describe the key structural features of the Watson-Crick DNA double helix.
Explain Replication: Describe the significance of ‘Semi-Conservative’ DNA replication.
Explain Translation: Describe the role of mRNA (codons) and tRNA (anticodons) in Protein Synthesis.
Know Inhibitors: Name two antibiotics that inhibit the 50S ribosomal subunit.

Frequently Asked Questions (FAQs)

Q1. What is Gout and why does it occur?

Gout is a type of inflammatory arthritis caused by hyperuricemia (excess uric acid in the blood), which is the end product of purine metabolism. Uric acid forms monosodium urate crystals that deposit in joints, leading to severe pain and inflammation.
Treatment: Allopurinol, a xanthine oxidase inhibitor, reduces uric acid production.

Q2. What is Semi-Conservative DNA Replication?

In semi-conservative DNA replication, each daughter DNA molecule contains one original (parental) strand and one newly synthesized strand. This model was confirmed by the Meselson–Stahl experiment (1958).

Q3. What are the properties of the Genetic Code?

The genetic code has the following properties:

  • Triplet codon (3 bases code for 1 amino acid)

  • Degenerate (multiple codons for the same amino acid)

  • Non-overlapping

  • Universal (common to almost all organisms)

  • Has a Start codon (AUG – Methionine)

  • Has three Stop codons (UAA, UAG, UGA)

Q4. How do Antibiotics inhibit Protein Synthesis?

Antibiotics target bacterial ribosomes (70S):

  • Aminoglycosides (e.g., Streptomycin) act on the 30S subunit

  • Chloramphenicol, Linezolid, and Macrolides act on the 50S subunit

They are selectively toxic because human ribosomes are 80S, structurally different from bacterial ribosomes.

Q5. What are the 3 types of RNA?

  • mRNA (Messenger RNA) – Carries genetic information from DNA to ribosomes

  • tRNA (Transfer RNA) – Brings amino acids during translation; contains an anticodon

  • rRNA (Ribosomal RNA) – Forms the structural and functional core of ribosomes