L42: Cell division, the cell cycle, and its controllers

• What is the state of interphase cells?

  They are NOT resting
• What happens to chromosomes during interphase?

  They become 'painted' and occupy territories
• Why is the structure of interphase chromosomes important?

  It allows access for transcription factors
• What begins to happen during early prophase?

  Centrosomes move to opposite poles
• What occurs to the chromosomes during late prophase?

  Chromosomes condense and become visible
• What happens to the nuclear membrane during late prophase?

  It completely breaks down
• What forms during metaphase?

  The metaphase plate is formed
• What is the significance of metaphase spreads?

  They are used for morphological studies
• What happens during anaphase?

  Sister chromatids separate into independent chromosomes
• What initiates cytokinesis?

  A cleavage furrow starts to form
• What occurs during telophase?

  Chromosomes uncoil and nuclear structure re-establishes
• What happens to spindle fibers during telophase?

  They depolymerise and become less distinct
• What happens after cytokinesis is complete?

  Each daughter cell enters a new interphase
• How do Interphase (G2) and Interphase (G1) differ?

  G2 prepares for mitosis, G1 is growth
• What are the phases of the cell cycle?

  • Interphase: G1, S, G2
  • Mitosis (M)
• What is the amount of DNA in a cell during G1, S, and G2 phases?

  G1: 2n, S: 4n, G2: 2n
• What is a characteristic of human reproduction?

  It is remarkably inefficient
• What can lead to mosaic aneuploidy in human embryos?

  Chromosome segregation errors
• What are the two parts of mitosis?

  1. Apportioning chromosomes equally
  2. Underlying control system (Cell Cycle)
• Who identified the first controller of the cell cycle?

  Sir Tim Hunt
• What is cyclin?

  A protein specified by maternal mRNA
• What happens to cyclin at each cleavage division?

  It is destroyed
• What is the pattern of protein expression in unfertilized eggs?

  • Characteristic pattern revealed over time
  • Radioactive proteins accumulate
• How do growing cells differ in protein expression from unfertilized eggs?

  They produce new proteins while others do not
• What happens to cyclin levels in fertilized eggs?

  • Cyclin levels rise and fall
  • Cycles with the cell cycle
• What is the role of cyclins in cell division?

  Cyclins control the timing of cell division
• When do cyclin levels peak in dividing cells?

  Just before cell division
• What happens to cyclin concentrations during the cell cycle?

  Cyclin concentrations rise and fall
• What is Tim Hunt's explanation regarding cyclins?

  Cyclins are continuously synthesized and destroyed
• What are the phases of the cell cycle?

  • G1 phase (first gap)
  • S phase (synthesis)
  • G2 phase (second gap)
  • M phase (mitosis)
• What is the function of cyclin-dependent kinases (CDKs)?

  CDKs partner with cyclins to regulate the cell cycle
• How many cyclins are known in Homo sapiens?

  At least 4 different cyclins
• How many CDKs are known in Homo sapiens?

  At least 4 different CDKs
• What is the role of cyclin/CDK heterodimers?

  • Regulate the cell cycle
  • Phosphorylate target proteins
  • Control progression through cell cycle phases
• What happens to activated cyclin/CDK complexes after their function?

  They are destroyed by proteolysis
• What do G1 cyclin-CDK complexes do?

  Prepare the cell for S phase
• What is the function of S phase cyclin-CDK complexes?

  Govern chromosome replication
• What do G2/M cyclin-CDK complexes do?

  Activate the mitotic apparatus
• What are the three sets of interphase cell cycle controllers?

  1. G1 phase complexes prepare for S phase
  2. S phase complex governs chromosome replication
  3. G2/M phase complexes activate the mitotic apparatus
• Who identified cyclins as controllers of the cell cycle?

  1. Beatriz Lagunas