Mitosis

Purpose

• To grow more cells– Example: Growing taller, growing roots

• To reproduce asexually– Example: Hydra buds to reproduce

• Repair damaged tissue– Example: A tear in skin –cells multiply to

repair the tissue.

Overview

• Cells divide into 2 daughter cells• Daughter cells are identical to parent cells• Done in somatic cells- typical body cells• There are 4 stages of mitosis:

– Prophase– Metaphase– Anaphase– Telophase/Cytokenesis

• The rest of the cell’s life is spent in interphase-the cell cycle.

Why study mitosis?

• Mitosis is a complicated process that is done flawlessly thousands of times per day.

• When mistakes occur, the result can be dangerous.

• Helps us to understand genetics and biotechnology.

Stage #1- Prophase

• Chromatin in the nucleus coils and become distinct chromosomes

• Chromosomes that were duplicated during the “S” phase join with their sister chromatid.—Join at the centromere

• A mitotic spindle grows out from centrosomes in the cytoplasm.

• The nuclear envelope disappears.

• Spindle attaches to the centromere (kineticore) and pulls the chromosomes to the center.

Stage #2-Metaphase

• Centrosomes are positioned at the poles.

• The chromosomes are lined up in the middle-the metaphase plate.

• The sister chromatids are lined up on either side of the plate.

• The spindle is attached to each chromatid and prepares for separation.

Stage #3-Anaphase

• The spindle fibers “reel” in the chromatids.

• The poles move farther apart.

• The microtubules which make up the spindle get shorter, pulling the chromatids toward the poles.

Stage #4-Telophase

• A nucleus begins to reform in the new cell.

• Chromosomes lengthen into chromatin.

• Mitotic spindle disappears.• A cleavage furrow appears,

separating the two cells.• Cytokenesis pinches the cell

into two separate cells.

Differences in mitosis

• Plant cells use telophase differently- they form a plate between the two new cells that becomes a cell wall.

Factors for mitosis

• Cells only divide when they are attached or anchored—anchorage dependence.

• Cells divide until they begin to touch one another-density-dependent inhibition

• These conditions prevent cells from dividing in the wrong environment or uncontrollably. --This is regulated by the cell cycle.