Histology Cell Cycle and Cell Division
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19 terms
Terms | Definitions |
|---|---|
 Overview of the Cell Cycle | - G1, S, G2, M, G0 |
| G0 Phase | - nondividing cell or cell population - inactive cell or cell performing normal functions - used to include cells in G1, S, G2 because they appear structurally the same - after mitosis, can choose to go into G0 (differentiate)--some will never divide again (neurons) and some will stay in G0 but divide again later if necessary (hepatocyte) |
| G1 | - pre-replication phase - variable length of time - cell prepares for S phase (or differentiates to enter G0 phase) - 2N |
| S | - DNA replication ("synthesis") phase - usually 6-7 hours - 4N |
| G2 | - post-replication phase - usually 2-3 hours - preparation for cell division - 4N |
| Karyokinesis | - nuclear division in cells undergoing division - division of DNA |
| Cytokinesis | - cytoplasmic division in cells undergoing division |
| Cancer and the Cell Cycle | - average length of cell cycle for cancer cell is 2-4 days (comparable to cell cycle times for normal cells with high turnover rate such as hemapoietic progenitors and GI mucosal cells) - suggests cancer is typically a disease of persistant proliferation (rather than rapid proliferation) - related to aging |
| Initiating Cell Division | - external stimulation = growth factors (bind to receptors, second messenger system, activate early intermediate gene) - CYCLIN--increases before cell division (G1); turns on a cdc2+/CDC28 kinase component of maturation promoting factor MPF - cell division begins with metaphase, cyclin is rapidly degraded after cell division, MPF then decreases - MPF functions: 1) condense DNA (into chromosomes) 2) spindle apparatus 3) nuclear envelope breakdown (phosphorylation of lamins leads to nuclear breakdown; dephosphorylation of lamins leads to reformation) - checkpoints |
| Checkpoints | - cycle is halted temporarily to allow error free completion of the previous phase - G1--is cell big enough? is environment favorable? - G2--is all DNA replicated? (plus two G1 questions) - M--are all chromosomes aligned on spindle? - if errors noticed, either repaired or cell undergoes apoptosis (see SYLLABUS) |
| DNA Replication | - semiconservative - opening the double helix (helicase, helix-destabilizing proteins, DNA topoisomerase) - replication 5' to 3' - Okazaki fragments (leading vs lagging, RNA primer, ligase) |
| Prophase | - disappearance of nucleolus - dissolution of nuclear envelope (due to phosphorylation of nuclear lamins by MPF) - chromosomes first appear (microscopical) |
| Metaphase | - chromosomes line up along equator randomly |
| Anaphase | - separation of chromatids and centromere - movement of chromatids to opposite poles (karyokinesis complete) |
| Telophase | - nuclear envelope reforms - chromosomes decondense, nucleolus reappears - completion of cytokinesis |
| Meiosis | - proceeded by G1, S, G2 phases - Reduction Division and Maturation Division SEE SYLLABUS (know pretty well) |
| Sex Chromosome Pairing | - X and Y not homologous--normal pairing of X and Y in prophase I is made possible due to "pseudoautosomal" regions in X and Y chromosomes - forms synaptonemal complex between X and Y chromosomes - sex chromosome aneuploidy often due to nondisjunction of sex chromosomes--Kleinfelter's syndrome (47, XXY) and Turner's Syndrome (45, X) |
| Lyon Hypothesis | - X-inactivation - only one X chromosome is active, any extra are inactivated ("heteropyknosis")--randomly chosen early in life, can be seen in nucleus as Barr Body (darkly stained intranuclear mass) - females--single Barr Body - males--zero Barr Bodies |
| Terminating Cell Division | - growth inhibiting factors (e.g. TGF-beta, interferons and TNF) bind to membrane receptors to inhibit cell division 1) decreased cyclin levels 2) spindle (microtubules) function 3) other mechanisms? |
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