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Unformatted text preview: Final Review Sheet – Week 10 Please Note: For Chapters 9, 14 and 15, we only skimmed the surface. You are responsible only for the material covered in the lecture. I suggest that you look through the Power Points and review sheets and if there are aspects that you don’t understand, read the relevant sections of the chapter. Lecture 25 Cell Cycle Regulation Main Points • In addition to motor proteins, there are many actin binding proteins, which may determine the state of polymerization of the actin, by sequestering monomers or capping polymers, or the shapes actin structures can form, by cross-linking actin filaments in a number of ways. • Non-muscle cells can move by a mechanism that involves only polymerization of actin, no motor protein. Migrating cells extend lamellopodia, extensions that project forward and contact the surface by forming focal adhesions. The extension of the lamellopodia is based on formation and extension • The cell cycle is now known to be divided into four phases, M, G1, S and G2. Based on light microscopy alone, the only distinctions that could be seen were between “interphase”, when nuclear membrane is intact and chromatin is dispersed, and M, when there is no nuclear membrane (in higher eukaryons) and chromosomes are condensed. • The first subdivision of interphase became clear with the use of radioactive thymidine to monitor the synthesis of DNA. An experiment was described in which cells were incubated with 3 H-thymidine for 30 minutes, then either fixed immediately or incubated longer in the presence of unlabeled thymidine. The only “labeled” DNA was the DNA synthesized in the 30 minute pulse. o Those cells fixed immediately showed label only over a subset of “interphase” cells. No mitotic cells were labeled, indicating that DNA synthesis does not occur during mitosis. o The fact that only a subset of interphase cells was labeled suggested that DNA synthesis does not occur throughout interphase, but only in a specific period of it. o With increasing “chase” periods, mitotic chromosomes became labeled. Using this sort of approach, researchers eventually identified and determined the lengths of G1, S and G2 • In another experiment, we discussed evidence that a cytoplasmic component in M cells stimulated condensation of chromosomes. In this experiment, cells at different phases of the cell cycle were fused together. When M cells were fused with cells of any other phase, the other cell’s chromosomes condensed (whether they had synthesized DNA or not) • Search for the cytoplasmic component was done using a bioassay involving frog oocytes that are arrested in meiosis. Injecting cytoplasmic extracts from cells at different phases of the cell cycle indicated that cells approaching mitosis contained a factor that could stimulate meiosis in this bioassay. The factor was called “MPF” for Maturation Promoting Factor. Final Review Sheet – Week 10 • Further studies showed that there is a protein that goes up and down with the cell...
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This test prep was uploaded on 04/08/2008 for the course BIOL 301 taught by Professor Tepperman during the Winter '08 term at University of Cincinnati.
- Winter '08