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Lecture 11

BIO130 Section 2 Lecture 11 and 12.docx

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Jane Mitchell

Lecture 11 and 12 the cell cycle The cell cycle o M phase the nucleus and cytoplasm dividemitosis nuclear division Cytokinesis cytoplasmic divisiono Interphase the period between cell divisionsG1 phase first gap phasewhen cell growth happensExtra cytoplasmic content of cell are growing and dividing S phase where DNA is replicated G2 phase second gap phase before cells enter the M phaseLength of phases depend on cell typeCell cycles in multicellular organisms o Many mature cells do not divide eg nerve cells muscle cells RBCAs they become specialized they lose ability to divideRBC after they grow lose their nucleus therefore they dont divide o Some cells only divide when given an appropriate stimulus eg liver cellswhen part of liver is surgically removed the remaining liver cells start to divide to replace the lost tissue o Some cells normally divide on an ongoing basis eg hematopoietic and epithelial stem cellsSome cells can also renew themselvesable to differentiate to more than one type of cellCells that do not continuously dividing are in GO liver needs special quos they have exited the cell cycle and they need a stimulus to put them back into the cell cycle o Cell cycle exit occurs M phase but before S phaseDrawn somewhere in G1 phasePrior to entry in S phasestart site check point Restriction pointCells need quo to proceed from G1 to S phaseThe cellcycle control system delays later events until the earlier events are complete o The major checkpoints start checkpoint allows cell cycle to go to S phase checks for favourable environment DNA damage etc G2M checkpoint ensures that all DNA is replicated and environment is favourable so it can be properly segregated to daughter cells o Metaphase to anaphase transition occurs at mitosis boundariesTriggers anaphase where chromosomes pulled to opposite pullsCheck if all chromosomes at spindles and connected ensures each daughter cell at right place1 copy eachProgression is determined by cycle dependent kinases allows cell to proceed to next phase of cell cycleWhen system malfunctionsexcess cell divisioncancerChromosom
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