DNA Replication Bidirectional and Rolling circle modes of replication.pptx

DNA Replication-Bidirectional and Rolling circle modes of replication

1. DNA REPLICATION Dr Sumitha J Associate Professor JBAS College for women,Chennai-18

2. DNA Replication: The process of copying DNA to produce two identical DNA molecules. Importance: Essential for cell division, growth, and genetic inheritance. Two Main Mechanisms: Bidirectional Replication Rolling Circle Replication

3. Overview: DNA replication initiates at a specific site called the origin of replication (ori). Replication proceeds bidirectionally from the origin, forming a replication fork. Involves both leading and lagging strand synthesis. Bidirectional Replication

4. Key Players: DNA Polymerase: Enzyme that synthesizes new DNA strands. Helicase: Unwinds the DNA double helix. Primase: Synthesizes short RNA primers to initiate DNA synthesis. Topoisomerase: Relieves the tension in the DNA helix. Single-Stranded Binding Proteins (SSBPs): Stabilize single-stranded DNA. Bidirectional Replication

5. Leading Strand Synthesis: Continuous synthesis in the 5' to 3' direction. DNA polymerase adds nucleotides directly to the growing strand. Lagging Strand Synthesis: Discontinuous synthesis in short fragments called Okazaki fragments. Primase synthesizes RNA primers. DNA polymerase extends the primers. DNA ligase joins the Okazaki fragments. Bidirectional Replication

6. Overview: Circular DNA molecule is nicked at a specific site. One strand is used as a template for continuous synthesis. The displaced strand can be used as a template for a new circular molecule. Key Players: Endonuclease: Enzyme that nicks the DNA molecule. DNA Polymerase: Synthesizes new DNA strands. Rolling Circle Replication

7. Key Components: Replication Fork: The Y-shaped structure formed when the double helix unwinds. Leading Strand: Synthesized continuously in the 5' to 3' direction, following the replication fork. Lagging Strand: Synthesized discontinuously in short fragments (Okazaki fragments) in the 5' to 3' direction, away from the replication fork. Rolling Circle Replication

8. DNA Polymerase: The enzyme responsible for synthesizing new DNA strands. Helicase: The enzyme that unwinds the double helix. Primase: The enzyme that synthesizes short RNA primers to initiate DNA synthesis. Single-Stranded Binding Proteins (SSBPs): Proteins that stabilize single-stranded DNA. DNA Ligase: The enzyme that joins the Okazaki fragments together. Rolling Circle Replication

9. 1. Initiation: Helicase unwinds the double helix at the origin of replication, creating a replication fork. Primase synthesizes a short RNA primer on the leading and lagging strands. 2.Leading Strand Synthesis: DNA polymerase adds nucleotides to the 3' end of the primer, continuously synthesizing the leading strand in the 5' to 3' direction. Rolling Circle Replication-Process:

10. 3.Lagging Strand Synthesis: Primase synthesizes multiple RNA primers on the lagging strand. DNA polymerase extends each primer, forming Okazaki fragments. DNA polymerase I removes the RNA primers and replaces them with DNA nucleotides. DNA ligase joins the Okazaki fragments together, forming a continuous DNA strand Rolling Circle Replication-Process: