1 / 17

Cell Division

Learn about cell division and the stages of the cell cycle. Understand how the cell cycle is controlled and the role of apoptosis in decreasing the number of cells.

wkathy
Télécharger la présentation

Cell Division

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cell Division

  2. Cell Increase and Decrease • Cell division increases the number of somatic cells • Consists of mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm) • Apoptosis, programmed cell death, decreases the number of cells

  3. The Cell Cycle • Cell cycle: orderly set of stages that take place between the time a cell divides and the time the resulting cells also divide.

  4. The Stages of Interphase • Most of the cell cycle is spent in interphase • In between episodes of mitosis • Cell carries on its usual functions • Prepares to divide (grows larger, number of organelles doubles, amount of DNA doubles) • Lasts 20 hours in mammals

  5. The Stages of Interphase • 3 stages • G1 occurs before DNA synthesis • S includes DNA synthesis • G2 occurs after DNA synthesis • G = growth • S = synthesis • M = mitosis

  6. The Stages of Interphase • G1 stage • Cell doubles its organelles • Accumulates materials needed for DNA synthesis

  7. The Stages of Interphase • S stage • DNA replication occurs • At the beginning of stage, each chromosome is composed of one DNA molecule (chromatid). At the end, each chromosome consists of two identical DNA molecules (sister chromatids) • DNA replication has resulted in duplicated chromosomes

  8. The Stages of Interphase • G2 stage • Cell synthesizes proteins needed for cell division • G0 stage • “Resting stage” • Cell is neither dividing nor preparing to divide • Ex. nerve cells

  9. The Mitotic Stage • Sister chromatids of each chromosome separate, becoming daughter chromosomes that are distributed to two daughter nuclei • After cytokinesis, two daughter cells are left • About 4 hours in mammal cells

  10. Control of the Cell Cycle • Controlled by internal and external signals. • Growth factors: hormones that act as external signals that regulate mitosis

  11. Control of the Cell Cycle • The stop signs represent checkpoints when the cell cycle can possibly stop

  12. Control of the Cell Cycle • Cyclin: protein that control the progression of cells through the cell cycle • Must be present from G2 to M, and G1 to S

  13. Control of the Cell Cycle • G1 checkpoint: cell cycle will stop if DNA is damaged • In mammals, protein p53 stops cell cycle at G1. • If p53 cannot repair DNA, will bring about apoptosis

  14. Control of the Cell Cycle • G2 checkpoint: Cell cycle stops if DNA has not finished replicating • If DNA is damaged, stopping the cell cycle allows time for damage to be repaired

  15. Control of the Cell Cycle • M checkpoint: Mitosis stops if chromosomes not properly aligned

  16. Apoptosis • Programmed cell death • Cell fragments engulfed by white blood cells or neighbouring cells

  17. Apoptosis • Cells harbour the enzymes that bring about apoptosis • Held in check by inhibitors • Unleashed by internal or external signals • “Initiators” receive signal to activate “executioners” which activate enzymes that dismantle cell • ex. executioners turn on enzymes that tear apart the cytoskeleton and enzymes that chop up DNA.

More Related