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Understanding Cell Division: Stages, Mistakes, and the Importance of Chromosomes

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Cell division is a crucial biological process that enables organisms to grow, repair damaged tissues, and reproduce. This process involves several stages: interphase, mitosis, and cytokinesis. During interphase, the cell prepares for division, replicating its DNA. Mitosis divides the nucleus into two sets of chromosomes, followed by cytokinesis, which divides the cytoplasm, forming two identical daughter cells. However, errors in this process can lead to uncontrolled growth and tumors, highlighting the importance of proper cell division in maintaining health.

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Understanding Cell Division: Stages, Mistakes, and the Importance of Chromosomes

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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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