1. Cell Growth and Division

2. Why do cells divide? DNA “Overload” DNA “Overload” –Not enough information for a big cell Exchanging Materials Exchanging Materials –Must be able to obtain nutrients and eliminate wastes easily Ratio of Surface Area to Volume Ratio of Surface Area to Volume –Volume increases faster than the surface area

3. Surface Area vs. Volume

4. Chromosomes DNA and proteins DNA and proteins Each chromosome consists of two identical sister chromatids Each chromosome consists of two identical sister chromatids Centromeres – area where the chromatids are attached Centromeres – area where the chromatids are attached

5. The Cell Cycle Series of events that cells go through as they grow and divide Series of events that cells go through as they grow and divide 4 phases 4 phases –M phase (mitosis and cytokinesis) – the division of the nucleus and the cell –G 1 phase (the first “gap”) – cells increase in size and synthesize new proteins and organelles –S phase (synthesis of DNA) – the chromosomes are replicated –G 2 phase (the second “gap”) – many of the organelles and molecules needed for mitosis are produced

6. The Cell Cycle

7. Interphase – G 1 + S + G 2 Interphase – G 1 + S + G 2 M phase M phase –Prophase –Metaphase –Anaphase –Telophase –Cytokinesis Mitosis

8. Interphase Cell spends most of its time in interphase Cell spends most of its time in interphase Cell grows Cell grows Carrying out basic cell functions Carrying out basic cell functions Making organelles Making organelles Copying chromosomes Copying chromosomes

9. Prophase Nucleoli disappear Nucleoli disappear Chromatin condenses (becomes shorter & thicker) Chromatin condenses (becomes shorter & thicker) Chromosomes become visible Chromosomes become visible Centrioles separate & move to opposite poles Centrioles separate & move to opposite poles Spindle fibers form between the centrioles Spindle fibers form between the centrioles Nuclear membrane disappears Nuclear membrane disappears

10. Metaphase Chromosomes attach to the spindle fibers at the centromere Chromosomes attach to the spindle fibers at the centromere Chromosomes align at the equator Chromosomes align at the equator

11. Anaphase Centromeres split apart Centromeres split apart Chromatids separate & move apart Chromatids separate & move apart Sister chromatids are pulled to opposite poles Sister chromatids are pulled to opposite poles

12. Telophase Cell membrane pinches together at the equator Cell membrane pinches together at the equator Nucleoli reappear Nucleoli reappear Nuclear membrane encloses each set of chromosomes Nuclear membrane encloses each set of chromosomes Chromosomes loosen up Chromosomes loosen up

13. Cytokinesis Division of the cytoplasm Division of the cytoplasm Begins during telophase Begins during telophase Cell membrane continues pinching until it separates forming 2 daughter cells Cell membrane continues pinching until it separates forming 2 daughter cells Plant cells have a cell plate that forms Plant cells have a cell plate that forms

14. Videos…

15. Life Spans of Human Cells

16. Controls on Cell Division Cell-to-cell contact – when cells come in contact with other cells, they stop dividing Cell-to-cell contact – when cells come in contact with other cells, they stop dividing

17. Cell Cycle Regulators Cyclin – a protein which regulates the cell cycle Cyclin – a protein which regulates the cell cycle –Cyclins bind to enzymes called cyclin- dependent kinases –Different cyclin/CDK combinations control different activities throughout the cycle Quality control checkpoints occur throughout the cycle Quality control checkpoints occur throughout the cycle –If something goes wrong the cycle stops

18. Cell Cycle Regulation

19. Cell Cycle Regulators Internal regulators – proteins that respond to events inside the cell Internal regulators – proteins that respond to events inside the cell –Part of the checkpoint process External regulators – proteins that respond to events outside the cell (e.g. growth factors) External regulators – proteins that respond to events outside the cell (e.g. growth factors) –Direct cells to speed up or slow down the cell cycle

20. Uncontrolled Cell Growth Cancer – uncontrolled cell growth Cancer – uncontrolled cell growth –Cells no longer respond to the control mechanisms –Occurs due to mutations in the DNA –Cancer cells crowd out normal cells, resulting in loss of tissue function Tumor – cluster of cancer cells Tumor – cluster of cancer cells Carcinogens – cancer causing substances Carcinogens – cancer causing substances

21. Cancer

22. Apoptosis Programmed cell death Programmed cell death Occurs when: Occurs when: –Webbing between human fingers and toes disappears before birth –Leaves fall from trees Also occurs in cells with DNA damage to prevent cancerous growths Also occurs in cells with DNA damage to prevent cancerous growths

23. Stem Cells Unspecialized cells that can become specialized under certain conditions Unspecialized cells that can become specialized under certain conditions Embryonic stem cells – unspecialized cells from an embryo Embryonic stem cells – unspecialized cells from an embryo –Can develop into a wide variety of specialized cells Adult stem cells – found in certain types of tissues Adult stem cells – found in certain types of tissues –Might be able to develop into different types of cells