Eukaryotic Cell Division: Mitosis

Pre-Assessment 1. Examine the picture of the cell. What phase is the cell in? A. prophase B. anaphase C. metaphase D. telophase 2. What is the structure labeled "X" on the picture? A. centriole B. spindle C. chromosome D. chromatid 3. During which phase does the DNA make a copy of itself? A. prophase B. metaphase C. interphase D. anaphase 4. During which phase do chromosome first become visible? A. interphase B. telophase C. metaphase D. prophase

Cell Cycle The cell cycle describes the behavior of cells as they grow and divide We will study the cycle which includes Mitosis and Cytokinesis Tumors (cancer) are the result of uncontrolled cell division and these can occur in any organ/tissue Mitosis Animation

**Note: Two chromatids make up a chromosome

Cell Cycle Interphase: Longest part of the cell cycle Includes G1, S and G2 G1: cell growth S: cell growth; replication of cell’s DNA G2: cell growth; organelles replicate DNA begins to condense into chromosomes

For a typical rapidly proliferating human cell with a total cycle time of 24 hours, the G1 phase might last about 11 hours, S phase about 8 hours, G2 about 4 hours, and M about 1 hour.

Phases of Mitosis: 1. Prophase Chromatin finishes condensing into chromosomes (visible under light microscope) Nucleolus/nuclear envelope broken down Spindle fibers form from centrosomes/centrioles with microtubules extending out Chromosomes appear as 2 identical sister chromatids joined together at centromeres

Prophase

2. Metaphase Longest stage of mitosis Chromosomes move to middle of cell (metaphase plate) Chromosome’s centromeres are on metaphase plate with sister chromatids each facing opposite sides of cell Centrosomes at opposite sides of cell

Metaphase

3. Anaphase: Shortest stage of mitosis Sister chromatids separate and begin moving towards opposite ends of cell (spindle fibers pull sister chromatids in via the centromere) and each one is now a “chromosome” Cell elongates At end of phase, each end of the cell contains complete and identical chromosomes

Anaphase

4. Telophase: Chromosomes are at each side of cell and nuclear envelope begins to re-form around Chromosomes elongate to form chromatin Spindle fibers disintegrate Cell is elongated and ready for cytokinesis

Telophase and Cytokinesis Cytokinesis: cell divides in two

Animal Cell Cytokinesis inward pinching of plasma membrane to form cleavage furrows

Plant Cell Cytokinesis cell plate forms and moves outward towards the sides of the cell from central region

Prophase Prometaphase Mid-prometaphase Metaphase Anaphase Telophase