1 / 23

The Cell Cycle

The Cell Cycle. Chromosomes duplicated and segregated into two genetically identical cells. Phases Of The Cell Cycle. S phase: DNA synthesis M phase: nuclear and cytoplasmic division G 1 , G 2 : gaps, monitor internal and external conditions. Morphological Changes During Cell Cycle.

mirabelle-nicolas
Download Presentation

The Cell Cycle

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. The Cell Cycle • Chromosomes duplicated and segregated into two genetically identical cells

  2. Phases Of The Cell Cycle • S phase: DNA synthesis • M phase: nuclear and cytoplasmic division • G1, G2: gaps, monitor internal and external conditions

  3. Morphological Changes During Cell Cycle • In metaphase replicated chromosomes aligned at equator • At anaphase sister chromosomes move to opposite poles

  4. Control Of Cell Cycle • System triggers series of events in correct order • Checkpoints: arrest cell cycle if previous events not completed or environment unfavorable

  5. Cyclin-Dependent Kinases • Cdks active when bound to cyclin • Cyclin-Cdk complexes promote passage through particular stages • Cyclins undergo cycles of synthesis and degradation

  6. Regulation Of Cdk Activity By Phosphorylation • Activating phosphorylation- requires activating kinase • Inhibitory phosphorylation- inhibitory kinase, removed by phosphatase

  7. Regulation Of Cdk Activity By Cdk Inhibitor Proteins • Inhibit activity of cyclin-Cdk complex • Prevent association of Cdk with cyclin

  8. Proteolysis of Cyclins • Cyclin degradation by transfer of ubiquitin • Mediated by ubiquitin ligases acting at particular stages • APC/C degrades M cyclins

  9. Initiation Of DNA Replication • S-cyclin-Cdk phosphorylates ORC for DNA replication to begin • Re-replication prevented by Cdc6 phosphorylation and inhibition by geminin

  10. Early Events Of Mitosis M-cyclin-Cdk phosphorylation of: • Nuclear lamins • Protein complex that mediates chromosome condensation • Proteins that regulate microtubules

  11. Anaphase • Triggered by APC/C ubiquitin ligase • APC/C targets degradation of separase inhibitor, resulting in cleavage of chromatid cohesion complex

  12. Exit From Mitosis • Chromosomes decondense, spindle disassembles, nuclear envelope reforms • Requires degradation of M-cyclin by APC/C-mediated ubiquitylation

  13. Control Of G1 Progression By Retinoblastoma Protein • G1-cyclin-Cdk phosphorylates Rb, resulting in release of E2F and transcription of S phase genes

  14. Mitogen Stimulation • Extracellular signals that stimulate G1- and G1/S-cyclin-Cdks

  15. Checkpoint Mechanisms • Mediated by Cdc25 phosphatase • DNA replication checkpoint: blocks G2→M • DNA damage checkpoint: blocks G2→M • Mediated by p53 • DNA damage checkpoint: blocks G1→S

  16. DNA Damage Checkpoint by p53 • DNA damage activates p53, which turns on p21 Cdk inhibitor

  17. Mechanics Of M Phase • Chromosomes condense • Mitotic spindle forms • Nuclear envelope breaks down • Chromosomes attach to spindle microtubules

  18. Chromosomes aligned at equator • Sister chromatids move to opposite poles

  19. Chromosomes at poles • Nuclear envelope reforms • Contractile ring of actin and myosin pinches cell in two

  20. Classes Of Spindle Microtubules • Three classes: kinetochore, overlap, astral • Participate in movement of chromosomes

  21. Movement At Anaphase • Anaphase A: chromosome movement toward poles by kinetochore MT shortening • Anaphase B: separation of poles by motor proteins and overlap MT elongation

  22. Forces at Anaphase A • Kinetochore microtubule depolymerization • Microtubule flux: prior to anaphase, tension generated from balanced tubulin addition (+), removal (-)

  23. Motor Proteins In Anaphase B • Pushing by plus end directed motors • Pulling by minus end directed motors

More Related