Cell Division

1. Cell Division Mitosis

2. Principles of Cell Division • All of the cells in your body began from 1 single celled egg, and 1 single celled sperm all of your cells came from those two cells • Cell division occurs both from growth and maintenance • Mitosis: A type of cell division in which daughter cells (product) receive the same number of chromosomes as the parent cell (starting point) • Cytokinesis: roughly equal division of cytoplasm Note: This is an area of current research and a lot of things are not yet known or well understood. 2nd Note: while things are refrred to as gendered (ex. Daughter cells/sister cells) these cells are not gender specific and do not have a gender

3. Components • Chromatin: all of the tangled fibrous complex of DNA and protein within eukaryotic cell nucleus • Chromosome: a single strand of DNA • Sister chromatids: two identical strands of DNA resulting from the duplication of the same strand of Chromosome attached by a centromere • Centrioles: small protein bundles found in animal cell cytoplasm • Spindle fibres: protein structures that guide chromosomes during cell division

4. The Cell Cycle • While described in phases, it actually doesn’t pause between steps but is instead a continuous process • Occurs at different rates depending on how often it is required (bone tissue in an infant vs. bone tissue in an elderly person)

5. Preparation • Before division begins is a very important step called interphase • Cell replicates DNA and prepares for nuclear division each chromosome is duplicated into sister chromatids • In humans we have 46 chromosomes, different species have different amounts • The cell spends almost 80% of its time in interphase

6. Mitosis • Prophase • Metaphase • Anaphase • Telophaseand Cytokinesis

7. Prophase • Early Prophase • Chromosome condense and become shorter and thicker • Centrioles move to opposite poles of thr cell • Spindle fibers start to form • Late Prophase • Chromosome continues condensing • Spindle fibers attach to centrioles • Nuclear membrane begins dissolving

8. Metaphase • Sister chromatids line up along the center of the cell (equatorial plate or metaphase plate). • Nuclear membrane completely dissolves • Spindle fibers attach the to the centrioles of the sister chromatids

9. Anaphase • Sister chromatids divide and an identical chromosome moves toward each of the centrioles.

10. Telophase and Cytokinesis • Chromosomes lengthen • Spindle fibers dissolve • Nuclean membrane forms around the chromosomes Cytokinesis • The cytoplasm and organelle are split between 2 new daughter cells. • Place where membrane divides is called the cleavage furrow

11. Cell Clock • Cells seem to have a limited amount of times that they can divide • When immature heart cells were frozen they were even able to remember how many times that had divided before hand. • If they had duplicated 10 times before being frozen, they would divide 40 more times after a thaw. • If they had been duplicated 30 times before they were frozen, they would divide another 20 times when they thawed. • Different cells have a different reproductive clock • Cancer cells do not seem to have a clock • Men produce 1 million sperm cells a day from puberty to well into old age • Your biological clock is a real thing (not just a saying for women in the 30s)