Chapter 9 – Cellular Reproduction Section 2 - Mitosis and Cytokinesis

Mitosis and Cytokinesis Eukaryotic cells reproduce by mitosis, the process of nuclear division, and cytokinesis, the process of cytoplasmic division.

Section 2 - Mitosis and Cytokinesis Cellular Reproduction Mitosis Mitosis is the division of the nucleus where the DNA is divided equally into two new nuclei. During the S (Synthesis) Phase of interphase, the DNA is copied.

Section 2 - Mitosis and Cytokinesis Cellular Reproduction Mitosis It is very important that all of the DNA gets copied correctly and equally divided among the new nuclei so that the 2 new cells are exactly the same. Incorrectly divided/copied DNA results in a mutation (permanent change in a cell’s DNA) and possible cell death.

There are 4 phases of Mitosis: Section 2 - Mitosis and Cytokinesis Cellular Reproduction The Stages of Mitosis There are 4 phases of Mitosis: Prophase Metaphase Anaphase Telophase

The Stages of Mitosis Prophase Section 2 - Mitosis and Cytokinesis Cellular Reproduction The Stages of Mitosis Prophase The cell’s chromatin tightens (coils and condenses) to form chromosomes (X). Each half of the X is a sister chromatid, and are attached at the centromere. Contain identical copies of DNA. Nucleolus disappears.

Cellular Reproduction Prophase Spindle fibers (microtubule structures) form in the cytoplasm. In animal cells, centrioles migrate to opposite poles. Aster fibers come out of the centrioles.

Near the end, the nuclear envelope seems to disappear. Cellular Reproduction Prophase Spindle fibers, centrioles, and asters, form a structure called the spindle apparatus. Near the end, the nuclear envelope seems to disappear. Spindle fibers attach to the sister chromatids and then to opposite poles.

Section 2 - Mitosis and Cytokinesis Cellular Reproduction Prophase

Section 2 - Mitosis and Cytokinesis Cellular Reproduction Metaphase Sister chromatids are pulled along the spindle apparatus toward the center of the cell. They line up in the middle (equator) of the cell.

Anaphase The microtubules of the spindle apparatus begin to shorten. Section 2 - Mitosis and Cytokinesis Cellular Reproduction Anaphase The microtubules of the spindle apparatus begin to shorten. The sister chromatids separate into two identical chromosomes. The chromosomes move toward the poles of the cell.

Telophase Chromosomes arrive at opposite poles. Section 2 - Mitosis and Cytokinesis Cellular Reproduction Telophase Chromosomes arrive at opposite poles. Chromosomes uncoil, unwind, or decondense into chromatin.

Section 2 - Mitosis and Cytokinesis Cellular Reproduction Telophase Two new nuclear membranes begin to form around the DNA and the nucleoli reappear. The spindle apparatus disassembles.

Section 2 - Mitosis and Cytokinesis Cellular Reproduction Cytokinesis Cytokinesis is the final step of the cell cycle where the cell’s cytoplasm divides into 2 new cells with identical nuclei. In animal cells, microfilaments constrict, or pinch (furrow), the cytoplasm.

Section 2 - Mitosis and Cytokinesis Cellular Reproduction Cytokinesis

Cytokinesis Plant Cells Do not have centrioles, but do have a spindle. Section 2 - Mitosis and Cytokinesis Cellular Reproduction Cytokinesis Plant Cells Do not have centrioles, but do have a spindle. Instead of pinching in half, a plant cell forms a cell plate (from membranes of the Golgi). A membrane and a cell wall then forms on each side of the cell plate.

Plant Cells

Prokaryotic cells Divide (reproduce) by binary fission. Have a circular chromosome and do not have a cell cycle. DNA is duplicated and the organism splits into two new cells with the same genetic material.

Binary Fission

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