UMass Amherst BIOLOGY 285 - Bio 285 SI Before Quiz 4 (4 pages)

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Bio 285 SI Before Quiz 4



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Bio 285 SI Before Quiz 4

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4
School:
University of Massachusetts Amherst
Course:
Biology 285 - Cellular & Molecular Biology
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Bio 285 SI Notes Quiz 4 Cell cycle control system CDK enzyme called Cyclin dependent kinase o Cyclin is a binding partner o master cell cycle regulator o Any point in cell cycle that cells decide they need to stop inhibit CDK CDK is regulated in several ways o Cyclin regulation different cyclins for different phases of the cell cycle G1 cyclins telling CDK to target G1 proteins S phase cyclins M phase cyclins o Phosphorylation dephosphorylation by kinases and phosphatases 1 o CDK inhibitors CDKIs 2 Another way of regulation is the regulation of Cyclin levels 3 o Regulate the levels of the cyclin that binds CDK Cyclin levels rise and fall throughout cell cycle via o Transcription translation o Degradation through ubiquitin mediated proteolysis Difference between CDK and cyclin CDK is the car while cyclin is the key Cell cycle checkpoints G1 phase o Check for DNA damage before replication begins o Check for favorable environment o Must have enough material to create a duplication of the cell S phase o Check for errors incompletely duplicated DNA G2 phase o Damaged or incorrectly replicated DNA o Enough resources to continue M phase o Proper chromosome and microtubule attachment and arrangement If DNA gets messed up can stop it during those checkpoints S G2 do basically the same thing Summarize whole cell cycle by putting each step in each stage Overview of cell cycle G1 phase growth gap phase o Could duplicate organelles o Cell checks environment Growth factor signals present Enough nutrients Enough energy DNA check for damage o Restriction point START G1 checkpoint o Prepare for DNA replication prepare ingredients Make nucleotides Make proteins required for replication o Once replication starts cell now in S phase S phase synthesis phase o DNA replication G2 phase 2nd growth phase o Check for DNA damage o Finish replication o Prepare for M phase M phase chromosome segregation o Cytokinesis splitting of the cytosol G0 phase non dividing state o Stop replication o Cell damaged etc Control of the replicative cycle Goal is to set up where the replication begins Replication begins at origin of recognition site on DNA o Multiple ORCs that occur at same time Form the pre RC o How Get ORC to bind to origin of replication ORC then recruits Cdc6 which recruits CDT1 which recruits Mcm then Mcm Cdc6 CDT1 ORC complex makes up pre RC complex Still in G1 to S phase transition o Once pre RC complex together start replication Now in S phase Have more than one ORC not all fire at one time o Mcm is the helicase only protein from pre RC physically involved in replication o Cdc6 CDT1 ORC all ATPases Stop replication from happening a second time Phosphorylate ORC it can t call recruit Cdc6 or CDT1 again phosphorylate Mcm it leaves nucleus phosphorylate Cdc6 it gets degraded o S phase cyclin CDK phosphorylates all these o Have to do all three to stop replication o Do all three to have multiple areas so you have more control over it Three locks on a door low chance of them all breaking compared to having one lock and having it break G2 phase prepping for chromosome segregation M cyclin levels rise on a graph solid line at bottom CDK activity CDK activity quickly rises then immediately falls on graph as M cyclin levels drop so does CDK o S phase M cyclin levels are rising but no CDK activity o M phase see a spike in CDK activity CDK bound to M cyclin o M CDK inactive at this state 2 kinases Wee1 Cak add phosphates to M CDK o Wee1 adds a phosphate that inhibits M CDK o Cak adds a P that activates M CDK Have both M CDK still inactive even though 2 phosphates Cdc25 takes off a phosphate from M CDK takes phosphate from Wee1 o Cdc25 is a phosphatase because it takes off a phosphate that takes off the inhibiting phosphate M CDK now active only has phosphate from Cak M CDK finds an inactive Cdc25 activates it by adding a P o Active Cdc25 now finds more inactive M CDKs and activates them process then goes on and on This is a positive feedback loop what causes jump in graph Why does cell do this When moving from G2 to M phase G2 is a growing phase cell doesn t want to divide too quickly why needs inhibitory phosphate when cell has grown enough you want it to divide so instead of having to wait for phosphate to be taken off AND cyclins to be made easy to just have to take phosphates off have already made cyclins Drop in CDK activity on graph is because cyclins get degraded o Once cyclins get destroyed CDK activity decreases If you phosphorylate Wee1 you inhibit it inhibiting inhibitory kinase which increases cyclin creation o Same as when phosphorylate Bad you inhibit Bad from doing its job Sequential phosphorylation Final goal to move cell cycle forward in order Example Have a substrate CDK adds a P to that substrate point here to activate PLK1 as a result PLK1 is still inactive when it binds to the substrate its phosphorylation then its active Spindle assembly Spindles made of microtubules which are made of tubulins Tubulins are GTPases o Made up of alpha beta tubulin Centrosome vs centrioles vs centromeres o Centrosome made of centrioles Located on spindle poles o Centromere in middle of chromosome where kinetochore sits Segment of chromosome DNA where kinetochores are on Insert spindle assembly picture 3 types of microtubules aster attached to side of cell interpolar in middle kinetochore attached to kinetochore Microtubules have polarity not charged just positive or negative o Growth happens on positive end polymerization depolymerization positive end located opposite from the spindle pole o Negative polarity embedded in the spindle pole Microtubule picture 1 is interpolar 2 is kinetochore 3 is aster Dynein walks towards negative end kinesin walks towards positive end Dynein stationary pulling pole away from it negative end going towards dynein positive end going away from dynein Eg5 holds onto 2 microtubules at the same time feet on both ends stuck in place not moving only legs are moving drags microtubules to the opposite way it s walking o Eg5 moves towards positive end o As you push microtubule tubulins get added to plus end so Eg5 has more length to walk on causes poles to move away from each other o Eg5 keeps microtubules at a common distance don t overlap too much o Eg5 only located on interpolar needs 2 microtubules Q take out Eg5 but everything else is normal what happens o Collapse microtubules get longer added to but don t move get longer overlap over microtubules What s the final goal of Eg5


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