Lecture Notes: M Phase of the Cell Cycle
Overview of the Cell Cycle
- The cell cycle consists of several phases:
- G1 Phase
- S Phase
- G2 Phase (collectively known as Interphase)
- M Phase: Represents cell division
M Phase Overview
- Includes:
- Mitosis: Division of the nucleus
- Cytokinesis: Division of the cytoplasm
Mitosis Phases
Mitosis is further divided into four phases:
-
Prophase
- Longest phase of mitosis.
- Chromatin condenses into chromosomes.
- Nucleolus disappears.
- DNA coils tightly into sister chromatids.
- Centromere connects sister chromatids.
- Spindle fibers extend from centrioles, moving to opposite poles.
- Nuclear membrane dissolves.
-
Metaphase
- Centrioles reach the poles.
- Spindle fibers align chromosomes at the cell equator.
- Sister chromatids positioned on either side of the equator.
-
Anaphase
- Spindle fibers shorten, separating sister chromatids at centromeres.
- Single-stranded chromosomes form a 'V' shape as they move.
- Chromosomes are pulled toward opposite poles.
-
Telophase
- Nuclear membrane reforms around each chromosome set.
- Chromosomes de-condense back into chromatin.
- Nucleolus becomes visible again.
- Mitosis is complete.
Cytokinesis
- Division of the Cytoplasm:
- In Animal Cells:
- Cell membrane pinches inward, forming two daughter cells.
- In Plant Cells:
- A cell plate forms along the equator, which develops into a new cell wall separating the daughter cells.
Key Points to Remember
- The M phase is the fourth and final phase of the cell cycle.
- Mitosis and cytokinesis are critical processes during the M phase:
- Mitosis: Nuclear division.
- Cytokinesis: Cytoplasmic division.
- Mitosis phases:
- Prophase: Chromatin to chromosomes, spindle fibers form.
- Metaphase: Chromosomes align at the equator.
- Anaphase: Chromatids separate to poles.
- Telophase: Nuclear membranes reform, chromosomes disperse.
- The M phase concludes with two identical daughter cells, maintaining genetic consistency with the original cell.