DNA Replication

Overview

• DNA is crucial as it codes for traits and directs cells.
• Essential in cell division to ensure daughter cells have DNA.
• Occurs in both prokaryotic and eukaryotic cells.

Location and Timing

• Eukaryotic Cells: DNA replication occurs in the nucleus during interphase, before mitosis or meiosis.
• Prokaryotic Cells: Lack a nucleus but still undergo DNA replication.

Key Players in DNA Replication

• Enzymes: Many key players are enzymes ending in "-ase." Enzymes speed up reactions.
  • Helicase: Unzips the DNA strands by breaking hydrogen bonds.
  • DNA Polymerase: Builds new DNA strands.
  • Primase: Creates RNA primers for DNA Polymerase to begin replication.
  • Ligase: Glues DNA fragments together.
  • SSB Proteins: Bind to single strands to prevent re-annealing.
  • Topoisomerase: Prevents supercoiling during replication.

Process of DNA Replication

1. Initiation: Origin
   • Replication starts at a specific DNA sequence known as the origin.
2. Unwinding
   • Helicase unwinds DNA.
   • SSB Proteins keep strands apart.
3. Primer Formation
   • Primase places RNA primers.
4. Strand Elongation
   • DNA Polymerase adds nucleotides in the 5’ to 3’ direction.
5. Lagging Strand Formation
   • Built discontinuously with Okazaki fragments.
   • Requires multiple primers.
6. Fragment Joining
   • Ligase seals gaps between Okazaki fragments.

DNA Structure

• DNA strands are anti-parallel: one runs 5’ to 3’, the other 3’ to 5’.
• Bases pair through hydrogen bonds: Adenine-Thymine, Guanine-Cytosine.

Directionality in DNA Replication

• Leading Strand: Continuously synthesized.
• Lagging Strand: Synthesized in fragments (Okazaki fragments) due to directionality.

Proofreading

• DNA Polymerase has proofreading abilities to minimize errors.

Importance and Applications

• Understanding DNA replication is crucial for medical treatments (e.g., targeting harmful cells like cancer).

Additional Insights

• Exploration beyond basic understanding can lead to significant scientific advancements.