Cell Cycle

Aka: Cell Cycle, Cellular Cycle, G0 Cell Phase, G1 Cell Phase, G2 Cell Phase, M Cell Phase, MItotic Phase, S Cell Phase, Mitotic S phase, Anaphase, Mitotic Anaphase, Metaphase, Mitotic Metaphase, Telophase, Mitotic Telophase, Mitosis, Interphase, Prophase, Mitotic Prophase, Cyclin-Dependent Kinase

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II. Definitions

  1. Cyclin-Dependent Kinase (CDK)
    1. Group of Protein kinase enzymes (Serine/Threonine kinase) that regulate Cell Cycle phases
    2. CDKs are composed of subunits including a catalytic subunit and an activating cyclin subunit

III. Physiology: Cell Cycle

  1. Interphase
    1. General
      1. Interval between cell divisions (includes G1, G0 and G2 Phases, as well as S Phase)
      2. Cell readies for Mitosis during Interphase, performing DNA Replication (S Phase)
      3. Chromosomes cannot be individually recognized during Interphase
    2. G1 Phase (Gap 1)
      1. Preparation for DNA synthesis (S-Phase) and Mitosis (M-Phase)
      2. Cells grow larger with increased cytoplasm, and organelles are duplicated
      3. Regulated by the availability of nutrients and growth factors, and suppressed by inhibitors
      4. Composed of 4 subphases
        1. Competence (response to growth factors)
        2. Entry (G1a)
        3. Progression (G1b)
        4. Assembly (G1c)
    3. G0 Phase (Gap 0)
      1. Following G1 phase, cells may further differentiate and not divide
      2. Cells may remain in G0 Phase for long periods of time
    4. Synthesis Phase (S-Phase)
      1. See DNA Replication
      2. Preparation for Mitosis and cell division
        1. Entire nuclear DNA content is replicated
        2. Centrioles (microtubule organizing structure) are duplicated
    5. G2 Phase (Gap 2)
      1. Gap following DNA synthesis (S-Phase) and preceding Mitosis (M-Phase)
      2. Chromosomes are tetraploid in G2 phase (four of each of 23 Chromosomes)
        1. Humans are otherwise diploid (pairs of Chromosomes known as 2N, totaling 46)
  2. Mitosis (M-Phase)
    1. General
      1. Cell Cycle phase in which nuclear division occurs
      2. Mitosis is in turn composed of 4 phases: Prophase, Metaphase, Anaphase and Telophase
    2. Phase 1: Prophase
      1. Chromosomes condense into individually differentiated structures
      2. Centrioles migrate toward the cellular poles
    3. Phase 2: Metaphase
      1. Chromosomes line up across the equatorial plane of the spindle, before separation
    4. Phase 3: Anaphase
      1. Chromosomes separate and migrate towards the poles of the spindle
    5. Phase 4: Telophase
      1. Chromosomes arrive at the poles of the cell
      2. Also marks the start of cytoplasm division

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