Lecture Notes: DNA and Its Structure

Introduction to DNA

• Mesmerizing Complexity
  • DNA is described as the most important and complex molecule.
  • DNA from a single cell, if untangled, would be taller than a human.
  • DNA in the human body could stretch to the sun 600 times.

DNA Basics

• Definition & Role

  • DNA (deoxyribonucleic acid) stores genetic instructions for cells.
  • It's a 6-billion-letter code for assembling life.

• Chromosomes

  • Humans have 46 chromosomes per somatic cell, each with a DNA molecule.
  • DNA is a nucleic acid alongside RNA (ribonucleic acid).

Structure of DNA

• Nucleotides

  • DNA is a polymer with repeating units called nucleotides.
  • Components of nucleotides:
    1. Five-carbon sugar (deoxyribose)
    2. Phosphate group
    3. One of four nitrogen bases: adenine (A), thymine (T), cytosine (C), guanine (G)

• Double Helix

  • DNA exists as a double helix structure.
  • Sugar-phosphate backbones form the structure's sides running in opposite directions (5' to 3' and 3' to 5').

• Base Pairing

  • Adenine pairs with thymine (A-T)
  • Guanine pairs with cytosine (G-C)
  • The base sequence determines genetic instructions.

DNA vs RNA

• Differences
  1. RNA is single-stranded.
  2. RNA contains ribose sugar (one more oxygen atom than deoxyribose).
  3. RNA has uracil (U) instead of thymine, pairing with adenine.

Historical Discoveries

• Key Figures
  • Friedrich Miescher discovered DNA in 1869.
  • Rosalind Franklin's x-ray diffraction work highlighted DNA's helical structure.
  • James Watson and Francis Crick built on earlier work, leading to the model of DNA structure.
  • Franklin's contributions were minimized in recognition due to timing and Nobel Prize rules.

DNA Replication

• Replication Process

  • Cells replicate DNA for division, creating identical copies trillions of times.

• Key Enzymes

  • Helicase: Unwinds the double helix.
  • DNA Polymerase: Adds new nucleotides; also proofreads for errors.
  • RNA Primase: Provides a primer for DNA polymerase.
  • DNA Ligase: Joins Okazaki fragments on the lagging strand.

Summary

• DNA is a highly celebrated molecule, integral to life and genetic information.
• Understanding its structure and replication is crucial for appreciating its role in biology.

Note: For further clarification or questions, refer to the detailed sections or reach out on social media platforms.