DNA Replication Lecture

Importance of DNA

• DNA is the ultimate director for cells, coding for traits.
• During cell division, new cells need a copy of DNA: introducing DNA replication.

Where and When DNA Replication Occurs

Where

• Eukaryotic cells: occurs in the nucleus.
• Prokaryotic cells: no nucleus, but replication still occurs.
• Differences exist between prokaryotic and eukaryotic DNA replication.

When

• Happens before cell division (mitosis or meiosis) during interphase.

Key Players in DNA Replication

• Helicase: Unzipping enzyme that separates the two DNA strands by breaking hydrogen bonds.
• DNA Polymerase: The builder that replicates DNA molecules to build new strands.
• Primase: The initializer that creates RNA primers so DNA Polymerase knows where to start.
• Ligase: The gluer that helps join DNA fragments together.

Process of DNA Replication

1. Origin: DNA replication starts at a specific DNA sequence identified as the origin.
2. Helicase: Unwinds DNA at the origin.
3. SSB Proteins: Bind to separated DNA strands to keep them apart.
4. Topoisomerase: Prevents supercoiling of DNA during replication.
5. Primase: Creates RNA primers on both DNA strands.
6. DNA Polymerase: Builds new DNA strands starting from the primers.

Anti-Parallel Strands

• DNA strands are anti-parallel: one runs 5’ to 3’, the other 3’ to 5’.
• DNA Polymerase can only build in the 5’ to 3’ direction.

Leading and Lagging Strands

• Leading Strand: Continuously built in the 5’ to 3’ direction.
• Lagging Strand: Built in fragments (Okazaki fragments) due to the antiparallel nature.
  • Primers are continuously placed for DNA Polymerase to build.
  • Ligase seals gaps between Okazaki fragments.

Result of DNA Replication

• Two identical double-helix DNA molecules, each with one old strand and one new strand (semi-conservative).

Proofreading

• DNA Polymerase has a proofreading capability to minimize errors.
• Corrects mismatched bases to avoid incorrect gene coding or protein synthesis.

Future Exploration

• Detailed understanding of DNA replication has led to medical treatments targeting harmful cells.
• Encouragement to explore further reading.

Conclusion

• Stay curious!