The cell cycle and cell division

1. The cell cycle and cell division Why is it called the cell cycle?

2. Before the cell can divide, DNA must be copied • Semiconservative- one old strand, one new strand • Increases accuracy After replication

3. The life cycle of a cell G1 can last for a few minutes or decades Genes control cell division Loss of control= cancer

4. How do cells die? “programmed cell death” injury

5. The stages of mitosis What do you get? Two identical cells

6. Why do cells divide? • So we can get bigger (cells don’t get bigger, we accumulate more cells) • To repair damage • Reproduction in some organisms • How many times can cells divide? • Embryonic stem cells- unlimited • Differentiated cells- it depends • Lack of regulation can lead to cancer • Can we control regulation?

7. Sexual reproduction and meiosis • Sperm and egg: deliver two halves of a genome • Some terminology: • Gametes: “sex cells” • Diploid: a cell with two copies of each chromosome • Diploid number: 2n • Haploid: a cell with one copy of each chromosome • Haploid number: n • Meiosis: cell division process by which gametes are formed

8. Karyotype: one chromosome comes form each parent

9. Meiosis Two rounds of cell division In humans, each daughter cell has 23 chromosomes

10. Many possible combinations of chromosomes are possible Random assortment Crossing over

11. Not identical in human males and females

12. Summary • The cell cycle is its life history. Not all cells in the body have the same history. • Cells divide by mitosis to form exact copies of themselves • Meiosis forms gametes, and is the basis of sexual reproduction