Cell Cycle Overview: M Phase vs Interphase

Cell Cycle and Mitosis

• Human cells have 46 chromosomes, which is a characteristic number for the species.
• Mitosis (M phase) is a continuous process with five subphases: Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.

Prophase

• Chromosomes condense and become visible in the light microscope.
• The spindle apparatus forms, made of microtubules that grow from microtubule-organizing centers (MTOCs).
• MTOCs define the two poles of the spindle apparatus.

Prometaphase

• The nuclear envelope breaks down.
• Microtubules attach to chromosomes at kinetochores, which form at the centromere of each chromosome.

Metaphase

• The mitotic spindle is complete, and chromosomes are lined up on the metaphase plate.
• Each chromosome is held by kinetochore microtubules from opposite poles.
• Astral microtubules hold the spindle poles in place.

Anaphase

• Sister chromatids are pulled apart by the spindle fibers toward opposite poles of the cell.
• Cohesins holding sister chromatids together split, and kinetochore microtubules shrink.

Telophase

• A new nuclear envelope begins to form around each set of chromosomes.
• The chromosomes begin to decondense, and mitosis is complete when two independent nuclei have formed.

Cytokinesis

• The cytoplasm divides to form two daughter cells.
• In plants, vesicles from the Golgi apparatus bring membrane and cell wall components to the middle of the cell, forming a cell plate.
• In animals, a ring of actin and myosin filaments contract inside the cell, pinching in to form a cleavage furrow and dividing the cell.

Cell Cycle Regulation

• The cell cycle is regulated by kinases (enzymes that attach a phosphate group to a protein) and phosphatases (enzymes that remove a phosphate group from a protein).
• The cell cycle is regulated to ensure proper cell growth and division.