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Unit 5 Topic 2: Regulating the cell cycle Growth factors: proteins secreted by "control" cells to regulate the cycles of other cells. There are 50 known growth factors. M checkpoint: occurs during metaphase; checks to see that all sister chromatids are attached to the appropriate centrosomes. G2 checkpoint: "proofreading" and repair of replicated DNA. When done, signals a “go-ahead” into mitosis. G1 checkpoint: if conditions are not appropriate (missing essential nutrients, not enough space, etc), the cell will not move into S phase. 2 Other factors that affect cell division: Section 10-3 Anchorage dependence: Many cells will divide only if they are attached to some kind of surface (another cell, an organ lining, the wall of a petri dish) Density Dependent Growth Inhibition Cells will stop dividing when the run out of space! Figure 8.8, p133 3 What happens if cell cycle regulation is not working properly? • Sometimes cell DNA gets damaged and that affects its ability to control the cell cycle. • Apoptosis • Apoptosis 2 • Cancer Two Types of Tumors Benign • Localized (does not spread) • Resemble normal cells • Grow more slowly (yrs) Malignant • Metastasizes (travels) by spreading through blood or lymph • Look different than normal cells • Grow more quickly (weeks/months) 5 6 Why are tumors harmful? Mutated cells… • Can’t carry out normal functions • Crowd out normal cells • Steal nutrients from normal cells 7 Cancer is always a genetic disease. Why? Mutations can be inherited or environmentally caused. Carcinogens - chemical, physical, or biological agents that cause cancer by mutating genes • • • • UV radiation Tobacco Some viruses Some chemicals What types of genes do carcinogens mutate? Proto-Oncogenes • Normally regulate the cell cycle and cell division • Mutation turns them into “oncogenes” • Oncogenes turn normal cells into malignant ones (uncontrolled growth and division) Tumor Suppressor Genes • Block cell growth and division • Mutation leads to inability to stop cell division • Gene p53 on chromosome 17 is an example 9 What does p53 do normally? 10 Malignant cancer cells Angiogenesis 11 Malignant cancer cells Are able to reproduce indefinitely (not density-dependent) Invade and metastasize 12 Normal versus Cancerous Fibroblast Cells Fibroblast cells are found in connective tissue