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The Cell Cycle and Cell Division

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  • Key roles of cell division
    Unicellular organisms: reproduction. Multicellular eukaryotes: development from fertilized egg, growth, and repair.
  • Difference between somatic cells and gametes
    Somatic cells are body cells with two sets of chromosomes. Gametes are reproductive cells with one set of chromosomes.
  • Sister chromatids and centromeres
    Sister chromatids are identical copies of a chromosome joined at a centromere by protein complexes called cohesins.
  • Phases of the cell cycle
    The cell cycle includes interphase (G1, S, G2 phases) and the mitotic phase (mitosis and cytokinesis).
  • What happens during S phase?
    DNA synthesis occurs, duplicating chromosomes to form sister chromatids.
  • Main events of mitosis
    Prophase, prometaphase, metaphase, anaphase, and telophase lead to equal chromosome separation into two daughter nuclei.
  • Role of the mitotic spindle
    The mitotic spindle, made of microtubules, organizes and separates chromosomes during mitosis.
  • How do kinetochore microtubules shorten during anaphase?
    They shorten at the kinetochore ends, pulling sister chromatids toward spindle poles.
  • Binary fission in bacteria
    Bacterial cell division where the chromosome replicates and the cell splits into two daughter cells.
  • Cell cycle checkpoints
    Control points (G1, G2, M) where the cell cycle can be paused to ensure proper division.
  • Molecular control at G2 checkpoint
    Cyclin-dependent kinases (Cdks) and cyclins regulate progression to mitosis by activating MPF.
  • G1 checkpoint function
    Determines if the cell will proceed to DNA synthesis or enter a resting state (G0).
  • M checkpoint function
    Ensures all chromosomes are properly attached to the spindle before anaphase proceeds.
  • Effect of platelet-derived growth factor (PDGF)
    PDGF stimulates cell division by signaling cells to pass the G1 checkpoint.
  • Density-dependent inhibition
    Normal cells stop dividing when crowded; cancer cells lose this control and divide uncontrollably.
  • Characteristics of cancer cells
    Cancer cells may produce their own growth factors, ignore growth signals, or have defective cell cycle controls.
  • Difference between benign and malignant tumors
    Benign tumors are localized; malignant tumors invade other tissues and can metastasize.
  • Chromosome sets in humans
    Humans have 23 pairs of chromosomes; diploid cells have two sets (2n), haploid gametes have one set (n).
  • Homologous chromosomes
    Pairs of chromosomes, one from each parent, that have the same genes but may have different alleles.
  • Three unique events in meiosis
    Synapsis and crossing over, homologous pairs align at metaphase plate, and separation of homologs during anaphase I.
  • Comparison of mitosis and meiosis
    Mitosis produces two identical diploid cells; meiosis produces four genetically diverse haploid cells.
  • Origins of genetic variation
    Independent assortment, crossing over, and random fertilization increase genetic diversity.
  • Independent assortment formula
    Number of chromosome combinations = \(2^n\), where n is haploid number.
  • Random fertilization
    Any sperm can fuse with any egg, creating about 70 trillion possible diploid combinations in humans.