DNA Replication 🧬

Key Concepts

• DNA replication is essential for cell division, allowing each daughter cell to have a copy of the DNA.
• Occurs in the nucleus of eukaryotic cells; prokaryotic cells have no nucleus.
• Must happen before cell division, during interphase in eukaryotes.

Main Players in DNA Replication

• Helicase: Unzips the double helix by breaking hydrogen bonds between DNA bases.
• DNA Polymerase: Adds new DNA bases to form a new strand of DNA.
• Primase: Makes RNA primers to indicate where DNA Polymerase should start.
• Ligase: Links DNA fragments together.
• SSB Proteins: Prevent re-annealing of single-stranded DNA.
• Topoisomerase: Prevents over-twisting of DNA.

Steps in DNA Replication

1. Origin of Replication: Specific DNA sequence where replication begins. Helicase unzips DNA here.
2. SSB Proteins: Bind to single strands to keep them apart.
3. Topoisomerase: Prevents DNA from over-twisting.
4. Primase: Creates RNA primers on both DNA strands.
5. DNA Polymerase: Builds new DNA strands in a 5’ to 3’ direction by adding bases to the 3’ end.
6. Leading Strand: Synthesized continuously in the direction of the replication fork.
7. Lagging Strand: Synthesized in fragments (Okazaki fragments) in the opposite direction of the replication fork.
8. Ligase: Joins Okazaki fragments together.

DNA Structure Basics

• DNA strands run anti-parallel (5’ to 3’ and 3’ to 5’ directions).
• Made up of sugar-phosphate backbone with nitrogenous bases (A, T, G, C).
• Adenine pairs with Thymine; Guanine pairs with Cytosine.
• Carbon atoms in sugar are numbered 1’ to 5’ to determine direction.

Semiconservative Replication

• Each new DNA molecule consists of one parental strand and one new strand.

Error Checking & Proofreading

• DNA Polymerase can proofread and correct mistakes during replication.
• Mistakes can lead to faulty proteins if not corrected.

Medical Relevance

• Understanding DNA replication has led to medical advances, including treatments that inhibit replication in pathogenic cells and cancer cells.

Further Reading

• Explore detailed aspects of DNA replication for advanced understanding.
• Recommendations available in video notes for more in-depth study.

Remember to stay curious!