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Lecture 17

Lecture 17 - Chapter 17 - Cell Cycle - March 19.docx

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York University
BIOL 2021
Patricia Lakin- Thomas

March 19, 2013 Chapter 17: Cell Cycle Cell Cycle  Figure 17-16  CDKs activated by binding cyclin dependant kinases  CDKs that are dependent 1. G1 – CDKs  Not required in all cells  Control activity of G1/S CDKs 2. G1/S CDKs  High in late G1, fall in S-phase  Trigger commitment to cell cycle entry (start) 3. S-CDKs  After start  S = Synthesis  stimulate chromosome duplication  Involved in M  High is S1, G2, early M 4. M-CDKs  Entry into mitosis  Drop in mid mitosis Activation and Inhibition of CDKs  CDKs controlled by phosphorylation  Cdk-activating kinase – CAK  Phosphorylate cdks to activate activating phosphate  Wee1 kinase inhibits Cdks “inhibitory phosphate” by putting an inhibitory phosphate 1. If Wee1 not made, lots of division but NO growth!  Cdc25 phosphate removes inhibitory phosphate, activates cdks 1. Most important for M-cdk control at mitosis  Figure 17-18 CAK inhibitory Proteins CKI  Bind to CDKs, inactivation important for G1/S CAKs and S CDKs Cyclical Proteolysis  Anaphase-promoting complex cyclosome  APC/C = APC  Ubiquitin ligase – transfers ubiquitin to protein and marks it for destruction  Target 1. Securin 2. S-cyclins 3. M-cyclins  APC activated by CDC 20 in anaphace  APC activated by Cdh1 in late mitosis – early G1  SCF = Ubiquitin Ligase – Fig 17-20a 1. Targets: CKI proteins in late G1 2. Activates S-cdk  DNA replication Transcriptional Regulation  Changes in cyclin gene expression in some cells 1. Mostly in G1/S and S cyclins  Figure 17-21**-Shows checkpoints Control of S phase  S phase – copy all DNA once and ONLY ONCE  DNA Synthesis – initiation at origin  elongation  Initiation at two stages: 1. Licensing  Permission to replicate at the origin  In late mitosis – thinking about the next cycle (also in early G1)  A complex of proteins (the pre-replicated complex = preRC) that will assemble at the origins of replication 2. Initiation  Beginning of S-phase  Activate S-cdk  Pre-initiation complex, forms around PreRC  Initiate DNA-synthesis  Pre-RC disassembled
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