BIOL 1st Edition Lecture 14 Outline of Last Lecture I Photosynthesis II Plants III How It Works IV The Circle of Life V Cell Cycle Outline of Current Lecture I Cell Division II Cytokinesis III Control of Cell Division IV Important Cell Cycle Control Points V Cell Control in Cancer Cells Current Lecture I Cell Division a 2 phases i Interphase a period of growth ii Mitosis Cytokinesis division of the nucleus and cytoplasm b Interphase i G1 cell grows and gets bigger ii S DNA replicated cell continues to grow iii G2 cell gets ready for mitosis and cytokinesis makes special proteins needed for that c Mitosis division of the nucleus d Prophase i Replicated chromosomes ii Nucleoli break down iii Spindle apparatus is formed serves to move chromosomes around e Prometaphase i Nuclear envelope breaks down ii Spindle apparatus attaches to replicated chromosome at the kinetochore protein complexes located at the centromere where sister chromatids are connected f Metaphase replicated chromosomes line up in single file in the center of the cell II III IV V g Anaphase sister chromatids separate and are pulled to opposite poles of the cell once the sister chromatids separate then they are bone fide chromosomes h Telophase i Chromosomes decondense chromatid ii Spindle apparatus disappears iii Nuclear envelope reforms Cytokinesis a Division of the cytoplasm b Animal cells i Cells are pinched apart ii First a cleavage furrow forms between 2 newly formed nuclei iii Microfilaments form a ring at the cleavage furrow and tighten to pinch 2 cells apart c Plant cells i Vesicles from golgi meet and fuse in center of the cell ii Forms 2 new membranes within single cell wall iii New cell wall forms between 2 new membranes Control of Cell Division a Important for a cell to know when to divide and when to stop dividing b Varies with cell type i Skin cells divide frequently throughout life ii Liver cells only divide for repair iii Nerve and muscle do not divide only get bigger c Mechanisms that control cell cycle are of intense interest i How normal cells regulate growth ii Understand how cancer cells escape the usual controls d Studied using tissue cultures grow cells in flask using artificial growth media i Normal cells in tissue culture grow and divide until they touch one another and then they stop growing contact inhibition ii Limited number of cell divisions normal cells divide 20 50 times then stop they age and die e Cancer Cells in tissue cultures behave differently from normal cells i Don t show contact inhibition ii Immortal they divide indefinitely Important cell cycle control points a Called checkpoints points in cycle where STOP and START signals are given b Molecular sensors check to see if all the right things have happened so far c Molecular brakes slow things down if things are going wrong d Apoptosis cell suicide if cell controls don t result in correction of a problem the cell may kill itself e 3 Checkpoints i G1 S checkpoint 1 Cell determines if its going to divide or not 2 Based on signals from environment and also on internal signals is cell big enough to divide 3 If cell passes the G1 S checkpoint then it is committed to divide it will go stepwise G1 S G2 M always completing each step before starting the next 4 If it decides not to divide it will exit the cell cycle and enter a non dividing stage G0 5 Most of the cells of the body are in G0 ii Checkpoints G2 and M are understood at some point at a molecular level Cancer Cell Checkpoints a Don t respond to cell cycle controls b If they do stop dividing it s often at the wrong pint c Results sometimes in cancer cell having wrong amount of DNA if they stop in the middle of S phase