• Cell Cycle: is a highly regulated series of events for the growth and reproduction of eukaryotic cells
    • Three stages: Interphase, Mitosis, & Cytokinesis
  • Smaller cells better because easier to coordinate chromosomes and microtubules with less ATP
  • DNA content doubles during Interphase (S phase) and halves during mitosis

Cell Cycle: Summary


  • Majority of cell cycle, split into 3 phases
    • All have metabolic activity & growth                                                                   

G1 Phase

  • Metabolic activity and growth; one chromatid

S Phase

  • DNA replication; two chromatids

G2 Phase

  • Prepares for cell division

M phase

  • Mitosis and cytokinesis

The G0 Cycle

  • If the cell does not receive the go ahead signal, it will exit the cycle, switching to a nondividing state called the G0 phase.
    • Can re-enter the cell cycle in response to appropriate cues.
  • Nondividing cells may exit the cell cycle or be held at a particular stage in it

How Does Mitosis Produce 2 Identical Daughter Cells

  • DNA Replication (Interphase) and separation of chromatids (Anaphase)                                                                     
  • Once duplicated, a chromosome consists of two sister chromatids, connected along their entire length
    • Before a cell divides, sister chromatids become individual chromosomes → ensure that daughter cells get a complete/identical set of chromosomes
  • Sister chromatids attached by cohesins and held most tightly by centromere: region of repetitive DNA sequences and proteins
    • Count chromosomes by number of centromeres but chromatids are double


  • Consists of mitotic fibers, centrosomes, and asters
    • Fibers made up of microtubules and proteins: control chromosome movement
      • Elongate by adding tubulin
    • Asters: microtubules that hold together two centrioles to make a centrosome
      • Spindle is complete when asters elongate and touch membrane
    • Two kinds of microtubules:
      • Kinetochore Microtubules: attach to kinetochores → move chromosomes to metaphase plate → jerk chromosomes back and form
      • Non-kinetochore microtubules: interact/overlap → elongate the cell as motor proteins push them from opposite poles using ATP