Cell Growth and Reproduction

1. Cell Growth and Reproduction October 2014

2. Cell Size and Limitations • What limits cell size? • Diffusion • Slow diffusion rate = need for small cell size • DNA • Protein production limits how large cells can be • Surface area-to-volume ratio • Plasma membrane would not have enough surface area for oxygen, nutrients, and waste to diffuse

3. Cell Reproduction • Why is it necessary? • To maintain a proper surface-to-volume ratio during growth • To replace cells that die • Example: replacement of skin cells that die and are sloughed off

4. Chromosomes • Structures in the nucleus of cells carry the genetic material that is copied and passed on from generation to generation • “Chroma” = colored/ “Soma” = body • Dark staining structures • Visible just before and during cell division

5. Chromosome Structure • During majority of cell’s life, chromosomes exist as chromatin • Long strands of DNA wrapped around proteins called histones • As the nucleus starts to divide, chromatin coils and becomes tightly packed

7. The Cell Cycle • Sequence of growth and division of a cell • Two periods: Growth & Division • Phases: • Interphase • Mitosis: Nuclear division; two daughter cells formed • Prophase • Metaphase • Anaphase • Telophase

8. Cell Cycle

9. Interphase • Majority of cell’s life spent in interphase • Three parts • Cell growth, protein production (G1) • DNA synthesis (S) • Shorter growth period (G2) • Mitochondria & other organelles are manufactured and cell parts needed for cell division are assembled

10. Mitosis: Prophase • 1st and longest phase of mitosis • Chromatin coils & becomes visible chromosomes • Nuclear envelope starts to disappear • In animal cells, centrioles migrate to opposite ends of the cell (no centrioles in plants) • Spindle begins to form

11. Mitosis: Metaphase • Short phase • Chromosomes attach to spindle fibers • Chromosomes are pulled by the spindle fibers and begin to line up at the midline (metaphase plate) • Important for each cell to receive an identical set of chromosomes

12. Mitosis: Anaphase • Separation of sister chromatids • Centromeres split apart • Chromatids pulled apart by shortening of the microtubules in the spindle fibers • Sister chromatids pulled toward opposite poles of the cell

13. Mitosis: Telophase • Final phase of mitosis • Chromatids reach opposite ends of cell • Chromosomes uncoil/unwind • Spindle breaks down • Nucleolus reappears • New nuclear membrane forms around new set of chromosomes • A new double membrane forms between the two new nuclei

14. Cytokinesis • Process where cytoplasm divides • In animal cells • Cell membrane “pinches” in to divide cell • In plant cells • Cell plate is formed until separation is complete

15. Levels of Organization(review) • Cells (ex. Neuron) • Tissues (ex. Nerve) • Organs (ex. Brain) • Organ systems (ex. Nervous System) • Organism (ex. Human)

16. Control of Cell Cycle • Cell cycle is controlled enzymes • Uncontrolled dividing of cells can result from • Failure to make certain enzymes, or • Production of these enzymes at the wrong time • The result of uncontrolled cell growth is cancer • a malignant growth resulting from uncontrolled cell division

18. Causes of Cancer • Environmental influences • Ex. Pollution, toxins • Cigarette smoke • Lung cancer • Over exposure to ultraviolet radiation (sun) • Skin Cancer • Viral infections • HPV (Human Papiloma Virus)  Cervical cancer

19. Suggestions for Cancer Prevention • Healthy lifestyle! • Diets low in fat and high in fiber (colon, breast and prostate cancer prevention) • Vitamins and minerals (Vitamins A, C, & E and Calcium) • Exercise • NO tobacco use