Cell division Occurs in the nucleus of eukaryotic cells by mitosis and meiosis Replacement of the entire lining of your small intestine Liver cells only divide for repairing Nerve cells do not divide Chromosomes Long and thin for replication and decoding Become short and fat prior mitosis → easier to separate due to compact form Meiosis (reduction division) During the production of sex cells (gametes) in animals In spore formation which precedes gamete production in plants Haploid gametes (sperm ovum) - sexual reproduction DNA in a cell replicates only once, but cell divides twice The Cell Cycle Interphase G1: Protein synthesis and growth (10 hours) Preparation for DNA replication (e.g. growths of mitochondria) Differentiation, only selected genes are used to perform different functions in each cell S: DNA Replication (9 hours) G2: short gap before mitosis, organelles and proteins for mitosis are made (4 hours) G0: Resting phase (nerve cells) M-phase Mitotic division of the nucleus (Prophase, Metaphase, Anaphase, Telophase) Cytokinesis (division of the cytoplasm) Interphase Phase with highest metabolism (mitochondria have a high activity) Muscles never complete the whole cycle Mitosis Process of producing 2 diploid daughter cells with the same DNA by copying their chromosomes (clones) Chromosomes can be grouped into homologous pairs Mitosis occurs in Growth Repair Replacement of cells with limiting life span (red blood, skin cells) Asexual replacement Controlled process, cancers result from uncontrolled mitosis of abnormal cells Division of the nucleus (karyokinesis) and the cytoplasm (cytokinesis) are two processes of mitosis Division of cytoplasm after nucleus. Delayed if cells have more than one nucleus (muscle) Active process that requires ATP Prophase Chromosomes become shorter and thicker by coiling themselves (condensation) This prevents tangling with other chromosomes Nuclear envelope disappears/breaks down Protein fibres (spindle microtubules) form Centrioles are moving toward opposite poles forming the spindle apparatus of microtubule Metaphase Centrioles at opposite poles Chromosomes line up on the equator of the spindle Centromeres (kinetochores) attach to spindle fibres Kinetochores consist of microtubules and "motor" proteins which utilise ATP to pull on the spindle Anaphase Spindle fibres pull copies of chromatids to spindle poles to separate them Mitochondria around spindle provide energy for movement Telophase Chromatid at the pole Sets of chromosomes form new nuclei Chromosomes become long and thin, uncoil! Nuclear envelopes form around the nucleus