M03.02.01 DNA Replication

Genetic information is transmitted from parent to progeny by the replication of parental DNA. During DNA replication, the two complementary strands of parental DNA are pulled apart. Each parental strand is then used as a template for synthesizing a new complementary strand, a process known as semiconservative replication. During cell division, each daughter cell receives one of the two identical DNA molecules.

Replication of Prokaryotic and Eukaryotic Chromosomes

DNA Replication Process

• Prokaryotic DNA Replication:
  • Starts at a single origin.
  • Two replication forks move away in opposite directions.
  • Results in two identical circular DNA molecules.
• Eukaryotic DNA Replication:
  • Multiple origins of replication.
  • Bidirectional replication from each origin.
  • Results in two identical linear DNA molecules (sister chromatids).
  • Occurs in the nucleus during the S phase of the cell cycle.
  • Sister chromatids are separated during mitosis.

Enzymes Involved in DNA Replication

• Polymerases: Enzymes that synthesize nucleic acids by forming phosphodiester (PDE) bonds.
• Nucleases: Enzymes that hydrolyze PDE bonds.
  • Exonucleases: Remove nucleotides from the 5′ or 3′ end.
  • Endonucleases: Cut within the nucleic acid, releasing fragments.

Chromosome Structure During the Cell Cycle

Stages of the Cell Cycle

• G1 Phase: Cell growth and preparation for DNA replication.
• S Phase: DNA replication.
• G2 Phase: Preparation for mitosis.
• M Phase (Mitosis): Division of the cell.

Eukaryotic Chromosome Replication

Diagram and Explanation:

• Panel A: Shows the chromosome during different phases of the cell cycle.
  • G1: Chromosome consists of one linear dsDNA molecule.
  • S: DNA replication occurs, forming two sister chromatids.
  • G2: Cell prepares for mitosis.
  • M: Chromosome condensation and separation of sister chromatids.
• Panel B: Different representations of a replicated eukaryotic chromosome.
  • A diagram of a replicated chromosome.
  • A stained image showing metaphase chromosomes, where chromatids and the centromere are visible.

Points to Remember

• Semiconservative Replication: Each daughter DNA molecule consists of one parental and one newly synthesized strand.
• Bidirectional Replication: In both prokaryotes and eukaryotes, replication proceeds in both directions from the origin.
• Cell Cycle Phases: DNA replication occurs during the S phase of the cell cycle in eukaryotes.

Bibliography

1. Molecular Biology of the Cell by Alberts B, Johnson A, Lewis J, et al. – Provides detailed mechanisms of DNA replication and the cell cycle.
2. Lehninger Principles of Biochemistry by Nelson DL, Cox MM – Covers the biochemical aspects of DNA replication and repair.
3. Medical Genetics by Jorde LB, Carey JC, Bamshad MJ – Discusses the implications of DNA replication in genetics and inherited diseases.