MHS 400 Mitosis

Mammalian Mitosis

Mitosis is the process during which one cell gives rise to two daughter cells. The DNA of the cell is duplicated, condenses into chromosomes, pulled apart by the mitotic spindle, and split by cytokinesis into two daughter cells.

Mitosis is divided into four stages:

• Prophase - condensation of the chromosomes and formation of the mitotic spindle
• Metaphase - chromosomes form the metaphase plate at the center of the cell
• Anaphase - chromosomes move to opposite poles of the cell
• Telophase - reformation of daughter nuclei

Cytokinesis then splits the cytoplasm of the cell into the daughter cellls.

Courtesy of Ahmed Katsha, Science and Engineering Department, Raritan Valley Community College, Somerville, New Jersey.

Prophase

Prophase is often divided into two phases:

Early Prophase

DNA duplicates, starts condensing into chromosomes, and become visible. The mitotic spindle begins to form as microtubules emerge from the centrosomes. The nuclear envelope breaks down. Centrosomes move toward opposite poles of the cell.

• Early Prophase 1
• Early Prophase 2
• Early Prophase 3

Prometaphase

Chromosomes continue to condense. Microtubules of the mitotic spindles attach to the kinetochores of the chromosomes. The centrosomes continue to move towards opposite poles of the cell.

• Prometaphase 1
• Prometaphase 2
• Prometaphase 3 - chromosomes aligned near the center of mitotic spindle

Metaphase

The mitotic spindle is complete with each chromosome lined up at the middle of the spindle forming the metaphase plate. Each sister chromatid is attached to a microtubule radiating from opposite ends of the spindle.

• Metaphase 1
• Metaphase 2
• Metaphase 3
• Metaphase 4

Anaphase

The centromere holding sister chromatids breaks apart. Spindle microtubules shorten as the chromosomes are pulled toward opposite poles of the mitotic spindle. Other spindle fibers further elongate the cell.

• Anaphase 1 - early anaphase after separation of the chromatids
• Anaphase 2
• Anaphase 3
• Anaphase 4 - chromosomes arrive the opposite poles of the mitotic spindle

Telophase

Chromosomes arrive at opposite poles of the spindle and begin to decondense. The nuclear envelope begins to form around the two sets of identical chromosomes. The mitotic spindle breaks down.

• Telophase 1
• Telophase 2
• Telophase 3

Cytokinesis

Cytokinesis completes cell division by separation of the cytoplasm into two daughter cells. A contractile ring forms inside the plasma membrane at the former metaphase plate. The actin filaments pull inward forming the cleavage furrow. Eventually the membrane cleaves the cell forming the two daughter cells.

• Cytokinesis 1
• Cytokinesis 2
• Cytokinesis 3
• Cytokinesis 4