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CORNELL BIOMG 1350 - Cell Division Cycle

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BIOMG 1350 1st Edition Lecture 12Outline of Last Lecture I. Retrieval Pathway, EndocytosisOutline of Current Lecture II. Cell Division CycleIII.Four PhasesIV. CheckpointsV. Cyclin-CDKVI. CancerCurrent Lecture- Without modifications of lysosomal enzymes in the Golgi, the receptor will stay in the trans Golgi network however the enzyme will be secreted.- Early endosome late endosome  lysosome (maturation)- Cell Division Cycle:o Cell growth and chromosome recognition, chromosome segregation, segregate all organelles, cell divisiono Life began 3 billion years ago mechanism are likely to be highly conservedo Must double in volume, duplicate organelles, divide equallyo Cells have mechanism to coordinate cell growth and segregation - Four Stages:o M phase= mitosis nuclear division, cytokinesis two different cellso The rest is interphase: cell doubles in volume Three parts:- G1 between M and S- S phase: duplicates DNA- G2 between S and M (larger than a G1 cell)o Duration of the cell cycle varies greatly from one cell type to another Example: Bacteria cell cycle= 10-20 minutes (in optimal conditions) Most nerve cells never divide againo If there aren’t enough nutrients: In g1 phase cell asses its environment to see if it can continue on in the cell cycle once it decides to go through, it goes through usually always at the same rateThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Checkpoints:o During cell cycle to ensure prior events have occurred and they are correcto Delays progression of cell cycle to ensure that one process is completed before the next is startedo G1 Checkpoint: Check that the environment is appropriate is the environment favorable? if yes enter S phaseo G2 Checkpoint: DNA is all replicated and no damageso Mitosis Checkpoint: All chromosomes are attached to mitotic spindle cytokinesiso Activate a checkpoint means to delay the cell cycleo Satisfy a checkpoint means the process is OK and the cell cycle can proceed- Cyclin-CDK:o Kinase= enzymes that puts a phosphate on a specific substrate proteino Phosphatases take away the phosphate at the right timeo Kinase is present throughout the cell cycle whose activity is dependent on cyclins. It is only active in presence of cyclino Cyclin concentration varies during the cycleo Cyclin concentration increases throughout interphase and peaks in M phase thenfalls and CDK activity occurs during cyclin concentration peak Ex. M Cyclino G1 checkpoint: S cyclin increases activate S-CDK and phosphorylates a lot of substrate and tell cell to replicate DNA right before S phase drives through S phase at G2 checkpoint M cyclin increases and activates M-CDK and phosphorylates a lot of substrate that drive cells into M phase mitosis checkpoint S cyclin decreases during M phase M cyclin decreases in the middle of M phase Why isn’t MCDK active before G2 phase?o For CDK to be active, it must be phosphorylated at one site and dephosphorylated at another site CAK (activating) and Wee (inhibitory) both act on inactive mCDK  kinaseactivity is off, right before G2 phase CDC 25 phosphatase activated by G2 checkpoint and makes mCDK active by getting rid of inhibitory phosphate Cyclin gets rid of T-loop Abrupt increase in CDK activity because of activating phosphatase- Activating phosphatase is turned on partially by the G2 checkpoint.- M-CDK activity is done very quickly by:o G2 checkpoint leads to some active m-CDKo The small amount of active m-CDK phosphorylates CDC 25 and fully activates it, which in turn activates all the m-CDKo Positive feedback loopo Also, the inhibitory phosphate is phosphorylated by active m-CDK and inhibits the phosphateo If Wee was inhibited, the cells would enter M phase early and divide early and get smaller- Cyclin concentration increases throughout interphase- CDK inactivation is triggered by cyclin degradationo Ubiquitin is a small protein and can covalently link to proteinso Poly-ubiquitylation of a protein is a common signal in cells that marks the protein for destruction- Cancer:o G1 checkpoint is site at which cells determine if they can enter cell cycle based on signalso In animal cells, it is based on growth factorso When they commit to enter it, they complete the cell cycleo Differences in cell cycle length are usually dependent on time spent in G1 checkpoint (“start”)o Cells that wont divide again leave G1 and go to G0o DNA damage also stops cells at the G1 checkpoint P53:- Protein in the absence of DNA damage it is degraded- With damage, activation of protein kinases that phosphorylate p53, which stabilizes it against being degraded- P53 combines with a specific part of DNA and regulates expressionof p21 gene- Transcription of p21 increases--. Which produces cdk inhibitor protein inactivates s-CDK until everything is ok- Defective means mutations will accumulate. It is a tumor


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CORNELL BIOMG 1350 - Cell Division Cycle

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