Understanding DNA Structure and Replication

Aug 13, 2024

Lecture on DNA Structure and Replication

Introduction to DNA

  • DNA, or deoxyribonucleic acid, is a complex and essential molecule.
  • Stores genetic instructions for cellular activities.
  • Composed of a 6-billion letter code that assembles living organisms.
  • Every somatic cell in humans contains 46 chromosomes.
  • DNA is a polymer made of nucleotides.

Structure of DNA

  • DNA is a nucleic acid like RNA (ribonucleic acid).
  • It exists as a double-stranded molecule forming a double helix.
  • Each strand consists of a sugar-phosphate backbone (deoxyribose sugar).
  • Four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
  • Base pairs: A pairs with T, and G pairs with C, joined by hydrogen bonds.

DNA Composition

  1. Nucleotide Components:
    • Five-carbon sugar molecule.
    • Phosphate group.
    • One of the four nitrogenous bases.
  2. Double Helix:
    • Each strand runs in opposite directions: 5' to 3' and 3' to 5'.
    • Structure likened to twisted ladder with sugar-phosphate backbone.

Differences Between DNA and RNA

  • RNA is single-stranded, contains ribose sugar, and uracil instead of thymine.

Historical Background

  • DNA discovered in 1869 by Friedrich Miescher, initially called nuclein.
  • Rosalind Franklin contributed to understanding DNA's helical structure.
  • James Watson and Francis Crick credited with modeling the double helix.

DNA Replication

  • Essential for cell division and life cycle.
  • Entire genome replicated trillions of times during a lifetime.
  • Key Enzymes:
    • Helicase: Unwinds the double helix.
    • DNA Polymerase: Adds nucleotides in the 5' to 3' direction.
    • RNA Primase: Lays down RNA primer for DNA Polymerase.
    • DNA Ligase: Joins Okazaki fragments on the lagging strand.
  • Replication Process:
    • Leading strand synthesized continuously.
    • Lagging strand synthesized in Okazaki fragments due to directional challenges.
    • Proofreading by DNA Polymerase ensures high fidelity.

Significance and Conclusion

  • DNA is central to biological functions and highly celebrated.
  • Next session will focus on how DNA sequences translate into organism traits.

Questions and Further Discussion

  • Ask questions on platforms like Facebook or Twitter for clarifications.