Enzymes play crucial roles in facilitating each step.
Step 1: Separation of DNA Strands
Goal: Expose nitrogenous bases to act as a template for new DNA.
Process:
Helicase: Enzyme that breaks hydrogen bonds between nitrogenous bases, unzipping the DNA.
Topoisomerase: (Not crucial to remember) Stabilizes and untwists DNA.
Replication Fork:
Created at multiple locations to speed up replication.
Allows DNA to be copied in segments.
Step 2: Copying the Parent DNA
Preparation:
Primase: Adds an RNA primer (small RNA segment) to the parent DNA.
Primer serves as an anchor for new DNA synthesis.
DNA Synthesis:
DNA Polymerase: Matches and adds complementary bases to parent DNA, forming the daughter strand.
Directionality: DNA is always synthesized from 5' to 3' end.
Leading vs Lagging Strand:
Leading Strand:
Copied continuously in the direction of helicase movement.
Requires fewer RNA primers.
Lagging Strand:
Copied in fragments (Okazaki fragments) in opposite direction to helicase.
Requires more RNA primers.
Cannot copy the last segment completely.
Step 3: Polishing the Copied DNA
RNA Primer Removal:
DNA polymerase removes RNA primers and replaces them with DNA.
DNA Fragment Merging:
DNA Ligase: Glues DNA fragments together on the lagging strand.
Proofreading:
DNA polymerase checks and corrects mismatches to ensure accuracy.
Key Enzymes
Helicase: Unzips the DNA strands.
Primase: Adds RNA primer.
DNA Polymerase: Adds complementary bases, removes primers, and proofreads.
DNA Ligase: Joins DNA fragments.
Summary
The process ensures replication accuracy, creating two identical DNA strands. Each step involves precise enzyme actions to ensure efficient and correct DNA copying.