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Understanding DNA: Structure and Function

May 20, 2025

DNA - The Double Helix

Overview of the Nucleus

  • Nucleus: Small, dense body in a cell, known as the "control center."
  • Function: Controls cell activities including reproduction and heredity.

Chromosomes and DNA

  • Chromosomes: Microscopic, threadlike strands in the nucleus made of DNA.
  • Function of DNA: Controls protein production, which forms structural units and manages chemical processes in cells.

Genes and DNA

  • Genes: Segments of DNA coding for proteins, and thus traits (e.g., baldness, blue eyes).
  • DNA Makeup: Found in nucleus and organelles (mitochondria, chloroplasts); controls cell functions.

Structure of DNA

  • Discovery: Structure established by James Watson and Francis Crick in 1953.
  • Double Helix: Twisted ladder structure with sides made of sugar (deoxyribose) and phosphate.
  • Nitrogen Bases:
    • Purines: Adenine (A), Guanine (G)
    • Pyrimidines: Thymine (T), Cytosine (C)
  • Base-Pair Rule:
    • Adenine pairs with Thymine
    • Guanine pairs with Cytosine
  • Nucleotides: Composed of a base, deoxyribose sugar, and phosphate.

Messenger RNA (mRNA)

  • Function: Carries DNA messages to ribosomes.
  • Differences from DNA:
    • Single strand
    • Contains uracil (U) instead of thymine (T)
    • Sugar ribose instead of deoxyribose

DNA Replication

  • Purpose: Ensures new cells receive an exact DNA copy.
  • Semi-Conservative Process: Original strand is conserved.
  • Process: DNA unzips and new nucleotides are added.

The Blueprint of Life

  • DNA as a Blueprint: Tells cells how to build organisms.
  • Gene Expression: Cells can turn off genes not needed for specific functions.
  • Protein Synthesis:
    • mRNA travels to ribosomes.
    • Codons (three bases) specify amino acids.
    • Amino acids form proteins.

Key Terms and Concepts

  1. Nucleus is the control center.
  2. Gene: DNA segment coding for a protein.
  3. Chromosomes located in the nucleus.
  4. DNA found in mitochondria and chloroplasts.
  5. Watson and Crick discovered DNA structure.
  6. Semi-conservative replication retains half original DNA strand.
  7. DNA ladder sides: Sugar and phosphate.
  8. Nucleotide parts: Base, sugar, phosphate.
  9. Bases in DNA: Adenine, Thymine, Guanine, Cytosine.
  10. Sugars: Deoxyribose in DNA, Ribose in RNA.
  11. Base pairing: A-T, G-C.
  12. RNA acts as a messenger as DNA is too large to exit nucleus.
  13. Proteins synthesized at ribosomes.
  14. RNA vs DNA: Single strand, uracil instead of thymine, ribose sugar.
  15. DNA replication process.
  16. DNA shape: Double helix.
  17. Proteins made from amino acids.
  18. Uracil in mRNA, not in DNA.
  19. Cells have same DNA; expression varies for function.
  20. DNA is called the "Blueprint of Life" because it instructs cell construction.