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Topic 2.5

Topic 2.5. Stages, mistakes, and products. Why do cells divide?. Maintain efficient SA:VOL ratio Growth and development Cell differentiation Replace dead, damaged, or infected cells. New cells need DNA copies Embryonic development Asexual reproduction. It’s all about the chromosomes!.

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Topic 2.5

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  1. Topic 2.5 Stages, mistakes, and products

  2. Why do cells divide? • Maintain efficient SA:VOL ratio • Growth and development • Cell differentiation • Replace dead, damaged, or infected cells • New cells need DNA copies • Embryonic development • Asexual reproduction

  3. It’s all about the chromosomes! • Genes on chromosomes stored in the nucleus • Every chromosomes has two copies (mom/dad) • Different species = different chromosome # • Following mitosis new cells are diploid (2n)

  4. more chromosomes… HUMANS OTHER SPECIES Frogs – 13 pairs Corn – 10 pairs Dogs – 39 pairs Flatworm – 8 pairs Potato – 24 pairs Yeast – 16 pairs • Haploid; 23 pairs of chromosomes; n=23 • Diploid; 2n=46 • Somatic cells (body cells) have a full (two) set of chromosomes • Gametes (sex cells) are haploid (n); have a half set of chromosomes • Pair up with other half during fertilization

  5. What are chromosomes? Double helix Packed around histone Grouped into nucleosomes Packed together in supercoil Supercoils create chromosomes (un-replicated single DNA molecule) Centromere is the point at which sister chromatids are connected

  6. Interphase • Longest phase • Composed of three phases: G1, S, and G2 • G1: Metabolic reactions (e.g. protein synthesis), more organelles (mitochondria/chloroplasts)are produced, and cell growth occurs • S: Synthesis phase; replication of DNA (before replication chromosomes are one DNA molecule) • G2: Cell grows more and preparation for division

  7. MITOSIS(division of the nucleus, not the cell) P-M-A-T • PROPHASE • METAPHASE • ANAPHASE • TELOPHASE

  8. Chromatin supercoils into sister chromatids • Nuclear envelope and nucleolus disappear • Centrioles form spindle microtubules and begin to move to opposite poles of the cell Prophase

  9. Centromeres of sister chromatids line up at the equator • Spindle attaches to centromeres • Centrioles now at opposite poles Metaphase

  10. Typically, shortest phase • Centromeres divide and the sister chromatids are now chromosomes • End of anaphase each pole has a complete, identical set of chromosomes Anaphase

  11. Chromosomes are at each pole • Nuclear membrane (envelope) begins to re-form • Nucleoli reappear • Spindle disappears • Elongated cell, ready for cytokinesis Telophase

  12. Cytokinesis • After nuclear division cytokines begins • Result is two genetically identical daughter cells Animal Cell - Plasma membrane forms cleavage furrows Plant Cell - Cell wall forms a cell plate

  13. Mitotic Division – A Summary • Interphase: Exact copies of DNA are made - Cell grows and prepares for division • Prophase: DNA is supercoiled • Spindle forms • Nuclear membrane disappears • Metaphase: sister chromatids line up at the equator - Spindle attaches to centromere • Anaphase: Chromatids pulled apart to form chromosomes • Telophase: Chromosomes at the poles • Nuclei reform • Cytokinesis: Cytoplasm is pinched in half forming two genetically identical daughter cells

  14. When mitosis goes wrong! • A tumor is the uncontrolled growth of cells • Tumors can grow in any organ or tissue • Tissues exposed to carcinogens (e.g. tobacco smoke) or relatively active tissues (e.g. breast, skin, and cervical tissue) are most often associated with tumors

  15. Mutations in a gene that tells the cell to stop dividing can lead to cancer

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