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Cell Cycle & Mitosis Meiosis

Cell Cycle & Mitosis Meiosis. Context. All living things (cells) come from other living things (cells) Cell division is necessary for: Reproduction Growth and development Tissue renewal Cell cycle – describes the life cycle of a cell. Somatic Cells vs. Gametes. Somatic cells – body cells

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Cell Cycle & Mitosis Meiosis

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  1. Cell Cycle& MitosisMeiosis

  2. Context • All living things (cells) come from other living things (cells) • Cell division is necessary for: • Reproduction • Growth and development • Tissue renewal • Cell cycle – describes the life cycle of a cell

  3. Somatic Cells vs. Gametes • Somatic cells– body cells • Contain entire genome within nucleus (or two copies of every chromosome) • Gametes – sex cells (i.e. sperm or egg) • Contain only half (or one copy (from mom or dad) of every chromosome)

  4. Phases of the Cell Cycle • M (mitotic) phase: • When mitosis (cell division) occurs • Interphase: • G1(Gap 1) • Cell grows • S (Synthesis aka DNA replication) • Cell replicates DNA • G2 (Gap 2) • Cell grows and prepares for cell division

  5. Chromatin DNA + proteins (histones) in eukaryotic cells • Chromosome structures consisting of chromatin • Sister chromatid one half of a replicated chromosome

  6. Centromere point of connection between sister chromatids • Kinetochore protein complex found at centromere

  7. Centrosome organelle that organizes microtubules • Centriole animals cells only (function unknown)

  8. Phases of Mitosis (literal cell division) 1st- G2 of interphase • Nuclear envelope forms • Centrosomes (& centrioles in animal cells) appear 2nd- Prophase • Chromatin condenses into chromosomes • Mitotic spindle appears 3rd- Prometaphase • Nuclear envelope breaks up (fragments) • Microtubules attach to centromeres at kinetochore

  9. 4th – Metaphase • Chromosomes meet @ middle (metaphase plate) • Spindle fibers attached to each chromatid at kinetochore 5th – Anaphase • Two sister chromatids pull apart at centromere and move towards opposite end of cell (towards centrosomes)

  10. 6th – Telophase and Cytokinesis • Two daughter nuclei form from fragments of original nucleus • Chromatin becomes less condensed • Cytokinesis – division of cytoplasm and formation of two daughter cells • Animal cells  involves cleavage furrow • Plant cells  involves cell plate (formed by vesicles!)

  11. Reminder: Binary Fission (prokaryotic cell division)

  12. Cell Cycle Control • Frequency of cell division varies with cell type • RBCs every 24hr • Mature nerve cells never divide • Cell cycle checkpoints:

  13. Cyclin-dependent kinases (Cdk) • Kinase – an enzyme that activate or inactivate other proteins by phosphorylation • Cyclin – protein who’s concentration fluctuates cyclically

  14. Cancer • Cancer cells derive from normal cells gone wrong • Ex: Mutation in gene that regulates cell cycle checkpoint; now cell does not stop at that checkpoint but just keeps dividing. • Cancer cells also • Have no contact inhibition • Aren’t anchorage dependent (thus metastasize) • Express vascularization proteins (bring in blood vessels to feed tumor) • And so much more.

  15. Meiosis • Process whereby gametes (sex cells) are produced for sexual reproduction purposes • Eggs in female; sperm in male • Sexual reproduction  egg meets sperm = fertilization • Offspring have genetic variation • Asexual reproduction  mitotic cell division in single-celled eukaryotes (e.g. amoeba) • Clones (parent and offspring are identical)

  16. Diploid vs. Haploid • In humans, each somatic cell has 46 chromosomes(23 from mom & 23 from dad) or 23 homologous chromosomes (homologues) • Somatic cells are diploid (full set of chromosomes) or 2n • Gametes are haploid (half set) or n

  17. Steps of Meiosis • 2 rounds: • Meiosis I (4n to 2n) • Meiosis II (2n to n)

  18. Meiosis I • Interphase: • Diploid cell’s chromosomes duplicate during interphase (2n  4n) • Centrosomes replicate

  19. Prophase I • Chromosomes condense • Homologous pairs match up and become physically connected at synaptonemal complex via process called synapsis • CROSSING OVER  Genetic exchange of information between non-sister chromatids

  20. Metaphase I • Homologous pairs line up on metaphase plate in tetrads • Anaphase I • Homologous pairs split up BUT sister chromatids stay together! • Telophase I & Cytokinesis • 2 daughter cells, both 2n, which go on to divide again

  21. Meiosis II • Prophase II • Metaphase II • Chromosomes meet at metaphase plate; sister chromatids are NOT identical (due to crossing over) • Anaphase II • Centromeres of each chromosome separate (sister chromatids pull apart) • Telophase II and cytokinesis • 4 haploid non-identical daughter cells are produced

  22. End Result of Meiosis • 2n  4n  2n  n • Production of four haploid daughter cells all of which are genetically distinct from each other and the parent cell

  23. Genetic variation • Mutations in DNA • Crossing over during prophase I of meiosis followed by (hopefully) random sexual reproduction • Independent assortment of homologous pairs during metaphase I

  24. Independent Assortment

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