Chapter 9 – The Cellular Basis of Inheritance College Prep Biology Mr. Martino

9.1 All cells come from cells. Repair and Growth The outer layer of skin is dead, new living cells underneath replace the dead layer that rubs off. Growth from infant to adult results in trillions of cell divisions. Reproduction Asexual reproduction = one cell splits into two new cells (bacteria); genetic clone Sexual reproduction = two parents contribute to the offspring (sperm and egg); increases genetic variation

9.2 Dividing Cells - Overview Before cells can reproduce – they must undergo nuclear division Mitosis: the division of regular body (somatic) cells Meiosis: the division of cells that form sex (gamete) cells or germ cells Chromosome: a DNA molecule and its proteins Chromatin: long, thin threads of DNA and protein that eventually coils to become chromosomes as the cell gets ready to divide Centromere: region that joins the sister chromatids

Ex. Humans have 46 chromo. in each somatic (body) cell Chromosome # varies depending upon organism Ex. Humans have 46 chromo. in each somatic (body) cell Diploid: (2n) cells have a pair of each chromosome – somatic cells Haploid: (n) cell with only 1 of each chromosome – gamete (sex) cells

9.2 Cell Cycle G1 – growth S – DNA replication Cell division replaces old, worn out cells, or damaged cells Millions of cells divide every second in humans (nerve and muscles do not) Cell cycle: sequence of events from when daughters cells are formed until they form new ones Interphase: 90% of cell cycle – chromo. duplicate & cell grows G1 – growth S – DNA replication G2 – growth & checking of chromo.

Chromo. are clearly visible Division of most cells involves 2 processes that make op the M phase: 1. Mitosis: nucleus and chromo. divide Chromo. are clearly visible 2. Cytokinesis: cytoplasm divides Mitosis is unique to eukaryotes and very accurate

9.3 Mitosis - Overview Mitosis is a continuous process, but consists of 4 main stages: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase Spindle apparatus: special microtublues that move chromosomes

Interphase By G2, most of contents has been doubled Interphase: period of growth when the cell synthesizes new molecules and organelles By G2, most of contents has been doubled Chromatin has been doubled At least 1 nucleolus is visible

Prophase Chromatin fibers become more tightly coiled and folded – becoming chromosomes Sister chromatids are joined at centromeres Nucleoli disappear Nuclear envelope disappears Microtubules attach to chromosomes Sisters are starting to move

Metaphase Mitotic spindle is fully formed Chromosomes aligned at metaphase plate with centromeres on plate

Anaphase Begins when two sisters come apart – becoming chromosomes ATP powers the pull of the chromosomes (centromeres first) toward opposite poles Spindles not attached to chromosomes lengthen – elongating the cell Ends when chromosomes reach poles

Telophase and Cytokenesis Reverse of prophase Cell elongation continues Nuclei appear at poles Chromosomes uncoil becoming chromatin Nucleoli reappear Mitotic spindle disappears 2 identical daughter nuclei have formed Cytokinesis follows forming 2 identical cells

Animal Cell Mitosis

Plant Cell Mitosis

Division of Animal Cell Cytoplasm Cytokinesis typically occurs in telophase, although it can begin in late anaphase In animals, it is referred to as cleavage Cleavage furrow: shallow groove on cell surface which is the first sign of cleavage A ring of microfilaments acts like drawstrings and gradually pinches the cell in two

Division of Plant Cell Cytoplasm Vesicles collect at center of cell and eventually fuse to form the cell plate Cell plate grows outwards until it fuses with the cell membrane

Cell Division Video’s Bacteria Animation Embryogenesis Neuron Division Plant and Animal Cell Division Movies

9.4 Cancer cell grow and divide out of control Tumors and Cancer Benign tumor – abnormal mass of normal cells Sometimes cause health problems but can usually be removed by surgery Malignant tumor – masses of cells that result from reproduction of cancer cells Cancer – disease caused by severe disruption of the cell cycle which may result in death Metastasis – the spread of cancer cells from their original point

Cancer Treatment Malignant tumors can be removed by surgery, difficult to remove all of the tumor. Radiation treatment exposes the tumor to high levels of radiation (light or ionizing waves) that destroy the abnormal cells. Side effects: damage to ovaries and testes Chemotherapy treats the tumor with drugs that interfere with the spindle apparatus of the cancerous cells disrupting division Side effects: damage to hair follicles and nausea.