Phases of Mitosis

Introduction

Mitosis is a key concept in biology, often remembered but not fully understood in terms of its phases.
Purpose of Mitosis: Division of nuclei to produce two identical daughter cells.
- Essential for growth from a zygote to multicellular organism.
- Replaces old and dying cells.

Cell Cycle: Process of cell duplication.
- Interphase: Predominant phase where the cell grows and duplicates its DNA.
  - G1 Phase: Cell growth.
  - S Phase: DNA synthesis and duplication.
  - G2 Phase: Further growth.
- G0 Phase: Some cells (nerve/muscle) do not divide and thus enter this phase.

Outcome: Produces two cells, each entering their own cell cycle.
Comparison to a movie: Mitosis is a fluid process, more like a film than static snapshots.
Classic lab: Observing stained onion cell chromosomes under division.

Cell Membrane
- Divides in half, forming a cleavage furrow.
Nuclear Envelope
- Fragments and reforms in new cells.
Centrosomes and Microtubules
- Centrosomes replicate and form spindles.
- Centrioles (in animals) organize microtubules.
Chromosomes
- Comprised of DNA wrapped around histone proteins.
- Condense into visible structures during division.
- Sister Chromatids: Identical copies joined at the centromere.
- Kinetochore: Protein structure on chromatids attaching to spindle microtubules.

Interphase
- DNA duplication.
- Centrosome replication.
Prophase
- Chromosomes condense.
- Formation of mitotic spindle.
Prometaphase
- Nuclear envelope fragments.
- Microtubules attach to kinetochores.
Metaphase
- Chromosomes align at the metaphase plate.
- "Meet in the Middle."
Anaphase
- Sister chromatids separate and move apart.
Telophase and Cytokinesis
- New nuclei form around daughter chromosomes.
- Cleavage furrow forms, or cell plate in plants.

Mitosis ensures equal DNA division and cell replication.
Understanding each phase enables identification and comprehension of cell division processes.