4.5 Cell Cycle

Describe the events that occur in the cell cycle.

• The cell cycle is a highly regulated series of events that controls the growth and reproduction of eukaryotic cells.
  • i. The cell cycle consists of sequential stages of interphase (G1, S, G2), mitosis, and cytokinesis.
  • ii. G1 phase: The cell is metabolically active, duplicating organelles and cytosolic components.
  • iii. S phase: DNA is in the form of chromatin and replicates to form two sister chromatids connected at a centromere.
  • iv. G2 phase: Protein synthesis occurs, ATP is produced in large quantities, and centrosomes replicate.
  • v. A cell can enter a stage (G0) in which it no longer divides, but it can reenter the cell cycle in response to appropriate cues.
  • vi. Nondividing cells may exit the cell cycle or be held at a particular stage in the cell cycle.

Explain how mitosis results in the transmission of chromosomes from one generation of cells to the next.

• Mitosis is a process that ensures the transfer of a complete genome from a parent cell to two genetically identical daughter cells in eukaryotes.
  • i. Mitosis plays a role in growth, tissue repair, and asexual reproduction.
  • ii. Mitosis occurs in sequential steps (prophase, metaphase, anaphase, telophase) and alternates with interphase in the cell cycle.
  • iii. Prophase: Sister chromatids condense, mitotic spindle begins to form, and centrosomes move to opposite poles of the cell.
  • iv. Metaphase: Spindle fibers align chromosomes along the equator of the cell.
  • v. Anaphase: Paired sister chromatids separate as spindle fibers pull chromatids toward poles.
  • vi. Telophase: Mitotic spindle breaks down, a new nuclear envelope develops, and then the cytoplasm divides.
  • vii. Cytokinesis: A cleavage furrow forms in animal cells or a cell plate forms in plant cells, resulting in two new daughter cells. 90 Cell Communication and Cell Cycle UNIT 4