The Cell Cycle and Mitosis• Cell Division in Prokaryotes– Prokaryotes hav one circular chromosome– Binary Fission- the division of a prokaryotic cell

into two offspring cells• DNA is copied, forming two identical chromosomes• Cell grows until it reaches approximately twice the cell’s

original size

• Cell division in Eukaryotes–Cell Cycle –repeating set of events in life of

cell– Interphase- time between cell divisions• G1 phase- cells grow to mature size• S phase- cell’s DNA is copied (synthesized)• G2 phase- Time during which cell prepare fro

cell division–Cell Division:• Mitosis- the nucleus of cell divides• Cytokinesis- division of cell’s cytoplasm

• Cell division in Eukaryotes https://wps.prenhall.com/wps/media/objects/486/498658/CDA8_1/CDA8_1b/CDA8_1b.htm

• Stages of Mitosis– Prophase 1. DNA condenses

into chromosomes2. Centrosomes move

to opposite poles3. Mitotic spindle

starts to form

• Metaphase– Chromosomes move

to center of dividing cell

• Anaphase– Chromatids of each

chromosome separate and move toward opposite poles

• Telophase1. Spindle fibers

disassemble2. Chromosomes return

to a less tightly coiled chromatin state

3. Nuclear envelope forms around each set of chromosomes

4. Nucleolus forms in each of the newly forming cells

• Cytokinesis- division of cytoplasm– In Animal Cells

1. Cytokinesis begins with a pinching inward of the cell; cleavage furrow

2. Cleavage furrow pinches the one cell into two cells

– In Plant Cells1. Vesicles from Golgi

apparatus join together at midline of dividing cell to form Cell Plate

https://wps.prenhall.com/wps/media/objects/486/498658/CDA8_2/CDA8_2a/CDA8_2a.htm

• Control of Cell Division– Control occurs at 3 main checkpoints

1. Cell growth (G1) checkpoint- if cell is healthy and has grown to suitable size during G1 phase, proteins initiate DNA synthesis (S phase)

2. DNA synthesis (G2) checkpoint- DNA repair enzymes check the results of DNA replication. IF ok, then cell proceeds with mitosis

3. Mitosis checkpoint- if cell passes this checkpoint, proteins signal the cell to exit mitosis.

– Cancer, the uncontrolled growth of cells is caused by mutations in the checkpoint proteins