Why do cells divide? Populations of single-cell critters Multicellularity We all start out as a single cell…a zygote & become/remain multicellular 1

Binary Fission…in prokaryotes 2

Binary Fission..DNA duplicates 3

DNA separates & new cell wall divides cell in two 4

2 ‘new’ cells…identical 5

Eukaryotic cell cycle Cell is ‘born’ Duplicates DNA Grows to…size? Prepares to divide Divides=mitosis 6

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Control of mitosis:CYCLIN Cyclins are a family of proteins that control the progression of cells through the cell cycle. 9

Chromosomes duplicate…S Phase 10

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Kinetochore (centromere) Spindle fibers attach to kinetochore 15

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Mitosis produces identical offspring (2N---2N) 20

Importance??? Growth Replacement 21

Cancer? Unregulated mitosis Benign Malignant/ metastasis 22

Unlike normal cells, which respond to density-dependent inhibition, tumor cells continue to divide, and multiply at an increased rate until all available nutrient supplies are depleted. When tumor cells are benign, they remain at the original site. When they are malignant, however, the tumor quickly becomes invasive: at this point, the mass is known as cancer.

Sometimes, cancerous tumors contain cells capable of triggering the formation of blood vessels specifically designed to create a nutrient supply for the mass. Malignant cells then gain a pathway via which they can travel to other parts of the body. When this occurs, the tumor has metastasised.

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