Topic 2: Regulating the cell cycle Unit 5

2 G1 checkpoint: if conditions are not appropriate (missing essential nutrients, not enough space, etc), the cell will not move into S phase. Growth factors: proteins secreted by "control" cells to regulate the cycles of other cells. There are 50 known growth factors. G2 checkpoint: "proofreading" and repair of replicated DNA. When done, signals a “go-ahead” into mitosis. M checkpoint: occurs during metaphase; checks to see that all sister chromatids are attached to the appropriate centrosomes.

Density Dependent Growth Inhibition Section Figure 8.8, p133 Cells will stop dividing when the run out of space! Other factors that affect cell division: 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)

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 lymphMetastasizes Look different than normal cells Grow more quickly (weeks/months) 5

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Why are tumors harmful? Mutated cells… Can’t carry out normal functions Crowd out normal cells Steal nutrients from normal cells 7

Carcinogens - chemical, physical, or biological agents that cause cancer by mutating genes UV radiation Tobacco Some viruses Some chemicals Cancer is always a genetic disease. Why? Mutations can be inherited or environmentally caused.

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