Rucete ✏ Biology In a Nutshell
1. What Is DNA Replication?
- DNA replication is the process by which a cell copies its DNA before cell division.
- It occurs during the S phase of interphase.
- The result is two identical DNA molecules, each with one old strand and one new strand.
2. Semiconservative Replication
- Called semiconservative because each new DNA molecule consists of:
- One original (template) strand
- One newly synthesized strand
3. Key Enzymes and Proteins Involved
Helicase
- Unwinds the double helix at the replication fork
Single-Strand Binding Proteins (SSBs)
- Stabilize the unwound DNA strands and prevent them from re-annealing
Topoisomerase
- Relieves strain caused by DNA unwinding by cutting and rejoining DNA ahead of the replication fork
Primase
- Synthesizes short RNA primers to initiate DNA synthesis
DNA Polymerase
- Adds DNA nucleotides to the 3′ end of the primer
- Replaces RNA primers with DNA
DNA Ligase
- Joins Okazaki fragments on the lagging strand by sealing the sugar-phosphate backbone
4. Leading vs. Lagging Strand
Leading Strand
- Synthesized continuously in the direction of the replication fork
Lagging Strand
- Synthesized discontinuously in the opposite direction of the fork
- Forms Okazaki fragments that are later joined by DNA ligase
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Biology in a nutshell