Learning Objective: Explain the process of DNA replication in prokaryotes and eukaryotes, including the semiconservative mechanism, bidirectional replication, origins of replication, and the role of replication enzymes.
DNA Replication Overview
Genetic information is transmitted from parent to progeny by DNA replication, producing two daughter DNA molecules identical to the parental molecule.
- The two complementary parental strands are separated.
- Each strand serves as a template for the synthesis of a new complementary strand.
- This process is called semiconservative replication: each daughter molecule contains one parental strand and one newly synthesized strand.
- During cell division, each daughter cell receives one of the identical DNA molecules.
Activity
Replication in Prokaryotes vs Eukaryotes
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| DNA type | Circular dsDNA | Linear dsDNA |
| Origin of replication | Single origin | Multiple origins per chromosome |
| Replication | Bidirectional from a single origin | Bidirectional from each origin |
| End product | Two identical circular DNA molecules | Two identical linear DNA molecules (sister chromatids) |
| Cell cycle phase | Any phase (prokaryotes) | S phase (interphase) |
Mechanism in Prokaryotes:
- Circular chromosome separates to form two replication forks moving in opposite directions.
- Forks meet, producing two identical circular DNA molecules.
Mechanism in Eukaryotes:
- Linear chromosomes have multiple replication origins.
- Each origin forms two replication forks.
- Completion produces two identical sister chromatids, separated during mitosis.
Activity
Replication Enzymes
DNA polymerases:
Synthesize DNA by forming phosphodiester bonds (PDE).
Nucleases:
Hydrolyze PDE bonds:
- Exonucleases: remove nucleotides from the 5′ or 3′ ends
- Endonucleases: cut within the DNA strand, releasing fragments
