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The Cell Cycle Cell Cycle = life of a cell from its formation until it divides Functions of cell division: Reproduction, growth, tissue repair Genome = all of a cell’s genetic info (DNA) Prokaryote: single, circular chromosomeEukaryote: more than one linear chromosome (ex: human, 46 chromosomes) Each chromosome must be duplicated before cell division-Duplicated chromosome = 2 sister chromatids attached by a centromere -Somatic cells: body cells. Diploid (2n), have 2 of each type of chromosome. Divide by mitosis. In humans, 2n = 46.-Gametes: sex cells (sperm/egg). Haploid (n), have 1 of each type of chromosome. Divide by meiosis. In humans n = 23. Phases of the Cell Cycle-the mitotic phase alternates with interphase: G1 à S à G2 à mitosis à cytokinesis-Interphase – 90% of the cell cycle -G1 Phase: cell grows and carries out normal functions -S Phase: duplicates chromosomes -G2 Phase: prepares for cell division-M Phase (mitotic phase) -mitosis: nucleus divides -cytokinesis: cytoplasm divides Mitosis: prophase à metaphase à anaphase à telophase-Happens as a continuous process with observable structural features:-prophase: chromosomes become visible-metaphase: alignment of chromosomes at the equator-anaphase: separation of sister chromatids-telophase and cytokinesis: formation of 2 daughter cells More detail…G2 of interphase: chromatin duplicatedProphase: early mitotic spindle forms from aster (centrosomes w centriole pairs), chromosome formation consisting of 2 sister chromatidsPrometaphase: nuclear envelope fragments apart, centrosomes move to spindle poles, nonkinetochore microtubules extend from the centrosomes, kinetochore microtubules (connect to chromosomes) extend from centrosomes.Metaphase: centrosomes at spindle poles, form spindle, chromosomes line up at metaphase plate (equator of the cell)Telophase: nuclear envelope and nucleolus form, cleavage furrow (or cell plate) starts to formCytokinesis: cytoplasm of cell divided, cleavage furrow forms in animal cells, cell plate forms in plant cells During anaphase:-chromosomes are walked to the poles by motor proteins-kinetochore microtubules shorten at ends as they depolymerize Bacterial cells divide by binary fission-chromosome replication begins at an origin of replication-replication continues-replication finishes-two daughter cells result Cell Cycle Control System-Checkpoint = control point where STOP/GO signals regulate the cell cycle-3 major checkpoints: G1 checkpoint, G2 checkpoint, M-spindle checkpoint 1. G1 checkpoint (most important): -controlled by cell size, growth factors, environment -“GO” à completes whole cell cycle -“STOP” à cell enters nondividing state (G0 phase) nerve, muscle cells stay at G0; liver cells get called back from G0 2. G2 chackpoint: -controlled by DNA replication completion, DNA mutations, cell size 3. M-spindle (metaphase) checkpoint: -check spindle fiber (microtubule) attachment. -kinetochore = proteins associated with DNA at centromere Internal Regulatory Molecules-Kinases (cyclin-dependent kinase, Cdk) – protein enzyme controls cell cycle. Active when connected to cyclin-Cyclins – proteins which attach to kinases to activate them. Levels fluctuate in the cell cycle-MPF = maturation-promoting factor specific cyclin-Cdk complex which allows cells to pass G2 and go to M phase External Regulatory Factors-Growth Factor: proteins released by other cells to stimulate cell division-Density-dependent inhibition: crowded cells normally stop dividing. Cell-surface protein binds to adjoining cell to inhibit growth-Anchorage Dependence: cells must be attached to another cell or ECM to divide Cancer Cells-Cancer = disorder in which cells lose the ability to control growth by not responding to regulation-multistep process of about 5-7 genetic changes (for a human) for a cell to transform-loses anchorage dependency and density-dependent regulation-tumors = mass of abnormal cells -benign tumor: lump of cells remain at original site -malignant tumor: invasive – impairs functions of 1+ organs (called cancer) -metastasis: cells separate from tumor and travel to other parts of the body Cancer Prevention-Anyone can get cancer but there are ways to minimize risk: -don’t smoke, legal/illegal (includes cigs, pipe, hookah, chew, 2nd hand, vape) -use sun protection -exercise/stay active and keep weight at optimal level (not over or under) -eat 5-7 servings of fruit/veg per day or predominantly plant based diet -use screening/preventative measures (breast/testicle/mole checks) -practice safe sex
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