Cell Division

Overview

• Cell division is the process where a parent cell divides into two daughter cells.
• Occurs as part of the cell cycle where the cell grows and replicates its chromosomes.
• In eukaryotes, cell division occurs as mitosis (vegetative division) and meiosis (producing haploid gametes for sexual reproduction).
• Prokaryotes undergo binary fission for cell division.

Eukaryotic Cell Division

Types

• Mitosis: Produces genetically identical daughter cells, maintaining chromosome number.
• Meiosis: Produces four haploid daughter cells, reducing chromosome number. Involves two divisions.

The Cell Cycle

• Comprises interphase (G1, S, G2 phases) and M phase (mitosis/meiosis).
• Interphase: G1 (growth), S (DNA replication), G2 (final preparation for mitosis/meiosis).
• M Phase: Division of nucleus (mitosis/meiosis) followed by cytokinesis.

Checkpoints

• DNA damage is detected and repaired at various checkpoints.
• Checkpoints prevent progression by inhibiting cyclin-CDK complexes.
• p53 protein plays a crucial role in monitoring DNA damage.

Prokaryotic Cell Division

• Binary Fission: Genetic material segregated into two daughter cells.
• Involves the divisome complex for peptidoglycan synthesis during cell wall growth and division.

Mechanisms and Components

• Chromosomes: Replicated and separated into daughter cells.
• Spindle Fibers: Pull chromosomes apart during mitosis/meiosis.
• Cyclin and CDKs: Regulate progression through cell cycle.

Phases of Mitosis

1. Prophase: Chromatin condenses into chromosomes, spindle fibers form.
2. Prometaphase: Nuclear envelope breaks down, spindle fibers attach to kinetochores.
3. Metaphase: Chromosomes align on the metaphase plate.
4. Anaphase: Sister chromatids separate to opposite poles.
5. Telophase: Nuclear envelope reforms, cytokinesis begins.
6. Cytokinesis: Division of cytoplasm, resulting in two daughter cells.

DNA Damage and Repair

• DNA damage checkpoints at G1/S, G2/M, and metaphase/anaphase transitions.
• p53 and other kinases play a role in repair or apoptosis if damage is irreparable.

Evolution and History

• Historically, various hypotheses existed on cell proliferation.
• Barthélemy Charles Joseph Dumortier first described cell division in 1832.
• Cell division filmed for the first time in 1943.

Key Definitions

• Cyclin-Dependent Kinase (CDK): Enzymes that control cell cycle progression.
• Telomerase: Enzyme that rebuilds telomeres, allowing cancer cells to divide indefinitely.

Special Types

• Asynthetic Fission: A newly discovered form of cell division in zebrafish skin cells.

Summary

Cell division is a fundamental process essential for growth, reproduction, and repair in organisms. Understanding its mechanisms allows insights into biological development, genetic consistency, and potential applications in medical science.