1 / 14

The Cell Cycle and its Control Chapter 21.1

The Cell Cycle and its Control Chapter 21.1. By: Tori Walker. The Cell Cycle. Four Major Phases: G 1 Phase Cells synthesize RNA & proteins S (Synthesis) Phase Cell prepares for DNA synthesis & chromosome replication G 2 Phase Growth Phase M (Mitotic) Phase Replication process.

bert-montoya
Download Presentation

The Cell Cycle and its Control Chapter 21.1

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 and its ControlChapter 21.1 By: Tori Walker

  2. The Cell Cycle • Four Major Phases: • G1 Phase • Cells synthesize RNA & proteins • S (Synthesis) Phase • Cell prepares for DNA synthesis & chromosome replication • G2 Phase • Growth Phase • M (Mitotic) Phase • Replication process

  3. Mitosis • Interphase: • Phase between one M phase and the next • Prophase: • nuclear envelope is continuous with ER and retracts into the ER • Golgi membranes break down into vesicles

  4. Mitosis (cont.) • Metaphase: • Mitotic apparatus (made of a bundle of microtubules called the spindle) has been assembled • Kinetochore assembles at each centromere and associate with microtubules from opposite spindle poles

  5. Mitosis (cont.) • Anaphase: • Nuclear envelope reforms • Sister chromatids separate by means of motor proteins on the spindle microtubules • Telophase: • Mitotic spindle disassembles • Chromosomes decondense • Cytokenisis: • Cytoplasm divides • Golgi complex reforms

  6. After Mitosis • Cell enters the G1 Phase • Vertebrate cells and diploid yeasts are 2n here • Haploid yeasts are 1n here • In most multicellular organisms most cells exit G1 and enter the G0 phase where they can survive for days, weeks, or even the lifetime of the organism (nerve and eye lens cells)

  7. Cell Cycle Regulation • Cyclins • The regulatory subunits of the protein kinases that control the cell cycle • Cyclin-Dependent Kinases (CDK) • The catalytic subunits of the protein kinases • Must be associated with a cyclin in order to be activated • Which cyclin it binds to determines which proteins are phosphorylated by the cyclin-CDK complex

  8. Regulation (cont.) • 3 major classes of Cyclin-CDK complexes that control passage through the cell cycle: • G1 cyclin-CDK complex: • Expressed in first – produced when replication is stimulated in the cell • Activates transcription of genes that encode for enzymes which are required for DNA synthesisand the genes incoding S-phase cyclins and CDKs

  9. Cyclin-CDK Comples (cont.) 2) S-Phase Cyclin-CDK coplex: • Held in-check by inhibitors during G1 • G1 Cyclin-CDK complexes induce the degration of S-Phase Cyclin-CDK inhibitors which in turn releases active S-Phase Cyclin-CDK complexes • They phosphorylate regulatory sites in the proteins that form DNA pre-replication complexes. This activates initiation of DNA replication and inhibits reassembly of new pre-replication complexes (to prevent aneuploidy)

  10. Cyclin-CDK Comples (cont.) • Mitotic Cyclin-CDK complex: • Synthesized in S-Phase and In G2 but are inhibited until DNA synthesis is completed • Phosphorylate multiple proteins that promote chromosome condensation, retraction of nuclear envelope, assembly of mitotic spindle apparatus, and alignment of condensed chromosomes at the metaphase plate

  11. Regulation (cont.) • Anaphase-Promoting Complex (APC): • Marks certain regulatory proteins for degration • Securin • Protein substrate of APC that inhibits the APC from degrading the cross-linking proteins (regulatory protein) between sister chromatids • Degraded after the chromosomes are aligned in metamorphosis allowing the sister chromatids to be pulled to opposite spindle poles in anaphase.

  12. APC (cont.) • Once the chromosomes reach their location in the dividing cell late in anaphase, the APC subsequently directs degration of the mitotic cyclins. • This leads to a decrease in mitotic CDK activity which causes the now separated chromosomes to decondense, the nuclear envelope to re-form around the daughter-cell nuclei, and the golgi apparatus to reassemble during telophase

  13. After Cytokinesis • In early G1 of the next cell cycle, phosphatases dephosphorylate the proteins (which were phosphorylated by the S-Phase-CDK complex during the previous S-Phase) to form pre-replication complexes allowing them to form again and prepare for the next S-Phase

  14. Restriction Site • The point in late G1 where the passage through the cell cycle is independent of mitogens • 3 critical transitions through the cell cycle: • G1 S-Phase • Metaphase Anaphase • Anaphase Telophase and cytokinesis • These steps are irreversible because they are each triggered by the regulated degration of proteins which is an irreversible process Regulation of Cell Cycle

More Related