MCB 181 1st Edition Lecture 21Outline of Previous Lecture I. Control of the Cell CycleII. Clicker QuestionsOutline of Current Lecture I. Control of the Cell Cycle (Revisited)II. Cancer: Out of Control Cell DivisionCurrent LectureI. Control of the Cell Cyclea. Cell cycle length can vary greatly among cell typesi. G1 phase is practically eliminated in rapidly dividing cellsii. Non-dividing cells get permanently stuck in G1 phase; this arrested stage is called the G0 stateb. Cell Cycle Checkpointsi. Many other protein complexes are involved in regulating the cell cycle, either by holding cells in a particular stage or by stimulating their passage to the next stageii. In our bodies, cells without effective cell-cycle checkpoints keep growing and form a tumoriii. A cell-cycle checkpoint is a critical point in the cell cycle that is regulated iv. Three checkpoints have been identified, the most important of which occurs late in G1v. At each checkpoint, interactions between regulatory molecules determine whether a cell proceeds with divisionc. Factors that affect whether cells pass the G1 checkpointi. Cell size – cells must be large enough to split into two functional daughter cells. ii. Nutrient condition – there must be enough food for cells to grow.iii. Social signals – signaling molecules from other cells in a multicellular organism; and (4) tumor suppressors – regulatory proteins that can stop the cell cycleiv. DNA damage – if the DNA molecule is physically damaged, the protein p53 activates genes that either stops the cell cycle until the damage is repaired or leads to programmed cell death (apoptosis)II. Cancer: Out of Control Cell Divisiona. Cancer is a common, often lethal disease that affects many humans and other animalsb. Despite their differences, all cancers derive from cells in which cell-cycle checkpoints have failedc. A tumor forms when one or more cells in a multicellular organism begins to divide uncontrollablyd. Benign tumors are noninvasivee. Malignant tumors are invasive and can spread throughout the body via the blood or lymph and initiate new tumorsf. Mature cells often remain in the G0 stateg. However if they pass through the G1 checkpoint they continue on through mitosis and divide.h. Cancer is thought to arise from cells with defects in the G1
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