DNA Replication Lecture

Introduction to DNA

• DNA is the ultimate director for cells, coding for traits.
• Necessary to replicate DNA during cell division to ensure daughter cells receive genetic information.

Where and When Does DNA Replication Occur?

• Eukaryotic Cells: Occurs in the nucleus.
• Prokaryotic Cells: Lack a nucleus but still perform DNA replication.
• Timing: Takes place before cell division, specifically during interphase in eukaryotic cells (before mitosis or meiosis).

Key Enzymes in DNA Replication

• Enzymes: Typically identified by the suffix "-ase."
  • Catalyze reactions, build up, or break down molecules.

Major Enzymes:

• Helicase: Unzipping enzyme, breaks the hydrogen bonds between DNA strands.
• DNA Polymerase: The builder, replicates DNA by building new strands.
• Primase: The initializer, creates RNA primers for DNA polymerase to know where to start.
• Ligase: The gluer, connects DNA fragments.

Process of DNA Replication

• Start Point: Begins at a specific sequence called the origin.
• Helicase: Unwinds DNA at the origin.
• SSB Proteins: Bind to separated strands to prevent re-joining.
• Topoisomerase: Prevents supercoiling during replication.

Steps:

1. Primase lays down RNA primers on both DNA strands.
2. DNA Polymerase begins building new strands:
   • Strands are complementary and anti-parallel (5’ to 3’ and 3’ to 5’ directions).
   • Builds in the 5’ to 3’ direction only, adding bases to the 3’ end.
   • Leading Strand: Built continuously.
   • Lagging Strand: Built in Okazaki fragments due to directionality.
3. RNA Primers are replaced with DNA bases.
4. Ligase seals gaps between Okazaki fragments.

Result of DNA Replication

• Produces two identical double helix DNA molecules (semi-conservative).
  • Each new molecule contains one original strand and one new strand.

Proofreading and Error Correction

• DNA Polymerase performs proofreading to minimize errors.
• Mistakes can lead to incorrect genes or proteins.

Further Exploration

• Detailed understanding aids in medical treatments to halt DNA replication in harmful cells.
• Encouragement to explore more detailed resources and stay curious.