DNA Replication

Overview

• DNA: Codes for traits, ultimate director for cells
• DNA Replication: Making more DNA during cell division

Where and When

• Eukaryotic Cells: Occurs in the nucleus
• Prokaryotic Cells: No nucleus, still perform DNA replication
• Timing: Before cell division, during interphase (before mitosis or meiosis)

Key Players (Enzymes)

• Helicase: Unzips the DNA strands by breaking hydrogen bonds
• DNA Polymerase: Builds new DNA strands by replicating DNA molecules
• Primase: Creates RNA primer, helps DNA polymerase start replication
• Ligase: Glues together Okazaki fragments on the lagging strand

Process of DNA Replication

1. Origin: Certain DNA sequence where replication starts
2. Helicase: Unwinds DNA at the origin
3. SSB Proteins: Bind to DNA to keep strands separated
4. Topoisomerase: Prevents supercoiling
5. Primase: Creates RNA primers on both strands
6. DNA Polymerase: Builds new DNA strands 5’ to 3’ direction
7. Okazaki Fragments: Formed on the lagging strand, later Joined by Ligase

Important Concepts

• Strand Directionality: DNA strands are anti-parallel
  • One strand runs 5’ to 3’, the other 3’ to 5’
• Leading Strand: Continuous replication in 5’ to 3’ direction
• Lagging Strand: Discontinuous replication, needing multiple primers
• Semi-Conservative Replication: Each new DNA has one old and one new strand
• Proofreading: DNA polymerase can proofread to reduce errors

Applications

• Medical Treatments: Understanding replication helps develop treatments for harmful cells

Stay curious!