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.