Cell Cycle

• Cell cycle


  The series of stages that a cell goes through in order to copy all of its genetic material and eventually divide into two daughter cells
• Prokaryotic life initially proliferated billions of years ago through cell division
• Cell division is how new cells in our bodies form to replace the old ones
• Genome


  The complete set of genetic information in a cell
• Eukaryotic cells have many different linear DNA molecules called chromosomes
• Humans have 46 chromosomes in all their somatic cells, a set of 23 from each parent
• Chromatin


  DNA molecule wrapped around proteins called histones to form nucleosomes
• Sister chromatids


  Two identical copies of a chromosome attached at the centromere, which separate during cell division
• Phases of the cell cycle

  • M phase (mitotic phase)
  • Interphase
  • G1 phase
  • S phase
  • G2 phase
• G1 phase


  Cell growth phase
• S phase


  DNA replication phase
• G2 phase


  Cell growth and preparation for cell division
• M phase


  Cell division phase
• Cell cycle is regulated by small signaling molecules in the cytoplasm
• Checkpoints


  Moments during or in between phases where the cell must receive a specific signal to move forward
• Protein kinases


  Enzymes that activate or deactivate other proteins by phosphorylation
• Cyclins


  Proteins with greatly varying concentrations in the cell, that bind to and activate protein kinases
• Cyclin-dependent kinases


  Protein kinases that must be bound to a cyclin to become activated
• MPF complexes


  Maturation-promoting factors, formed by the coordination of cyclins and kinases, that allow the cell cycle to pass the G2 checkpoint and perform tasks throughout mitosis
• Restriction point


  Checkpoint in the G1 phase that must be overridden by a signal in order to continue to the rest of the cell cycle
• Density-dependent inhibition


  Cells stop dividing once they have filled up their container, due to surface proteins binding to receptors on adjacent cells
• Cancer involves cells dividing out of control, leading to the development of a tumor
• Cancer cells do not follow the normal signals that regulate the cell cycle
• Genetic mutations can alter proteins crucial for regulating the cell cycle, leading to cancer
• Cancer treatment must address the fundamental biological level of cell division and cell cycle regulation
• Cell cycle


  The lifespan of a eukaryotic somatic cell
• Somatic cell


  Any cell in the body of an organism except for sex cells such as sperm and egg cells
• Cell cycle


  1. Cell growth

  2. Cell division
• Interphase


  The state a cell spends most of its life in
• Phases of interphase


  • G1
  • S
  • G2
• G1 phase


  Cell is busy growing and carrying out its function
• Some cells such as muscle and nerve cells exit the cell cycle after G1 because they do not divide again
• S phase


  Cell makes a copy of its DNA
• G2 phase


  Cell undergoes further preparations for cell division
• M phase


  1. Mitosis (nuclear division)

  2. Cytokinesis (division of the cytoplasm)
• At the end of M phase, you have two daughter cells identical to each other and identical to the original cell
• Most cell growth and function happen during G1
• The cell enters the S phase when it needs to divide
• In G2, the cell undergoes further preparations for cell division
• The M phase consists of mitosis and cytokinesis