Phases of Mitosis

Introduction

• Mitosis is the division of the nuclei to ensure the production of two identical daughter cells from a parent cell.
• Essential for growth, development, and cell replacement in organisms.
• Part of the cell cycle, which includes growth and DNA replication.

Cell Cycle Overview

• Interphase
  • G1 Phase: Cell grows.
  • S Phase (Synthesis Phase): DNA is duplicated.
  • G2 Phase: Cell continues to grow.
  • G0 Phase: Cells like nerve and muscle cells may not divide, entering a resting phase.
• M Phase: Mitosis occurs here.

Observing Mitosis

• Most cells in interphase; nuclei are visible.
• Cells in various stages of division can be seen.

Mitosis as a Movie

• Mitosis is a continuous process, akin to a movie.
• Example: Sea urchin cell division.

Structures Involved in Mitosis

Cell Membrane

• Cell enlarges, then divides through a cleavage furrow, forming two cells.

Nuclear Envelope

• Fragments during division, reassembles as nuclei form in daughter cells.

Centrosomes

• Made of microtubules and centrioles.
• Forms spindle apparatus to help divide chromosomes.
• Replicates early in mitosis, organizes microtubules and spindles.

Chromosomes

• Contain genetic information (DNA).
• Consist of sister chromatids joined at the centromere.
• Kinetochore: Protein on chromatids that attaches to spindle microtubules.
• DNA condenses into visible chromosomes during mitosis.

Phases of Mitosis

Prophase

• DNA condenses into chromosomes.
• Mitotic spindle begins to form.

Prometaphase

• Nuclear envelope fragments.
• Microtubules attach to kinetochores on chromatids.

Metaphase

• Chromosomes align along the metaphase plate (center of the cell).

Anaphase

• Sister chromatids separate and move to opposite poles.

Telophase and Cytokinesis

• New nuclei form on each side of the cell.
• Cell elongates, cleavage furrow forms (or a cell plate in plant cells).
• Microtubules help elongate and divide the cell.
• Nuclear envelope reassembles around chromatids.

Transition Back to Interphase

• Daughter cells re-enter the cell cycle.

Mnemonic for Mitosis Phases

• IPMAT-C: Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.
• Interphase and cytokinesis are technically not part of mitosis.

Conclusion

• Mitosis ensures equal DNA distribution in daughter cells, critical for cellular replication and organismal growth.
• Understanding phases helps identify stages in cell division.