Genetics

Essay text:

chromatin condenses, visible as chromosome, becomes chromatid, fiber extend from the centromere 2. centrioles move to opposite poles of cell 3. Nucleolus disappear 4. Nuclear membrane breakdown aster is the beginning of the spindle Metaphase ? spindle fiber align chromosomes along the middle of cell ? helps to ensure chromosomes separate properly ? receive only 1 copy of each chromosome ? the chromosomes line up in the middle Kinetochore – the protein that connects the chromosomes to the spindle fiber track ? moves the chromosomes Anaphase – sister chromatids separate at kinectochores ? move to opposite poles ? pulled at centromeres ? pole move farther apart ? need ATP ? In anaphase protein holding together sister chromatids are inactived Telophase ? chromosomes arrive at opposite poles ? daughter nuclei form ? nucleoli form ? chromosomes disperse ? - no longer visible under microscope ? spindle fiber disperse ? cytokinesis begins, cell division Cytokinesis – physical separation of the cells into two daughter cells at the cleavage furrow In plant cells, they do not have a cleavage furrow, it forms a cell plate CELL DIVISION coordination of cell division ? timing of cell division ? rate of cell division are crucial for normal growth, development and maintenance frequency ? depend on cell type ? skin cells divide frequently throughout life ? liver cells retain ability to divide, bu keep it in reserve ? mature nerve cells and muscle cells do not divide at all after maturity cell cycle control -2 irreversible points in cell cycle ? - replication of genetic material ? - separation of sister chromatids ? cells can be put on hold at specific checkpoints checkpoint control system 3 major checkpoints- ? G1, most crucial, can DNA synthesis begin? ? G2 – has DNA synthesis been completed correctly? ? Anaphase – spindle checkpoint, can sister chromatids separate correctly? Activation of cell division ? cell communications – signals protein ? - activators ? -inhibitors internal signal promoting factor: ? cyclin ? - regulatory proteins ? - levels cycle in the cell ? CDKS ? - cycle dependent kinesis ? - enzyme activates cellular proteins ? Mpg – maturation (mitosis) promoting factor ? APC – anaphase promoting complex External signals Growth factor ? protein signals released by body cells that stimulate other cells to divide ? - density dependent inhibition ? -- crowded cells stop dividing ? -- mass of cells use up growth factor ? anchorage dependent ? - to divide cells must to be attached to a substitute Cancer what causes them: ? uv radiation ? chemical exposure ? radiation exposure ? heat ? smoking ? pollution ? age ? genetics Tumors ? Benign tumor, no threat ? Malignant tumors ? - cell leaves original site ? - lose attachment to near by cells ? - carried by blood and lymph system to other tissues ? - start more tumors – metastasis ? impair functions of organs throughout body chemotherapy kills rapidly dividing cells gleevec – targets enzyme proteins found only in tumor fells ? treatment for adult leukemia and stomach cancer ? first successful targeted drug