Overview
This lecture summarizes the process of DNA replication, detailing the steps and enzymes involved in synthesizing both the leading and lagging strands.
DNA Replication Overview
- DNA replication produces two identical DNA molecules from one original molecule.
- The process requires enzymes that unzip DNA and synthesize new strands using existing templates.
Leading Strand Synthesis
- The leading strand template runs 3' to 5' (right to left in the image).
- DNA polymerase adds nucleotides in the 5' to 3' direction, following the helicase.
- DNA helicase unwinds the DNA double helix, separating the two strands.
- Single-strand binding proteins keep DNA strands apart to prevent reannealing.
- An RNA primer is first added by RNA primase to provide a binding site for DNA polymerase.
- DNA polymerase extends the DNA strand continuously as the DNA unwinds.
Lagging Strand Synthesis
- The lagging strand template runs 5' to 3' (right to left), so DNA polymerase works discontinuously.
- DNA polymerase synthesizes short DNA segments called Okazaki fragments in a 5' to 3' direction (left to right).
- RNA primase places multiple RNA primers along the strand, providing start points for DNA polymerase.
- DNA polymerase stops synthesizing each fragment when it encounters the next RNA primer.
- Later, the Okazaki fragments are connected to form a complete strand.
Key Terms & Definitions
- DNA polymerase — Enzyme that adds new DNA nucleotides in a 5' to 3' direction.
- DNA helicase — Enzyme that unwinds and separates the two DNA strands.
- Single-strand binding protein — Proteins that prevent separated DNA strands from rejoining.
- RNA primase — Enzyme that synthesizes short RNA primers to start DNA synthesis.
- RNA primer — Short RNA sequence providing a starting point for DNA polymerase.
- Okazaki fragment — Short DNA fragment synthesized on the lagging strand during replication.
Action Items / Next Steps
- Review class materials and diagrams on DNA replication for further understanding.
- Prepare for the upcoming test by practicing identifying enzymes and steps in DNA replication.