week 2 lecture 1: cell reproduction, senescence, and death 1

• give 3 external factors that control cell division

  1. population density
  2. cytokines (growth factors)
  3. substratum signals
• give 2 internal factors that control cell division

  1. activity of proliferation genes
  2. activity of anti-proliferation genes
• cell division is dependent on signals and sensors in the cell, such as receptors and enzymes
• If signals and/or sensors become damaged, cell division becomes unregulated
• what happens when unregulated dividing cells do not die?

  they form a tumour (swelling)
• what is tumorigenesis?

  the formation of a tumour in the body
• tumorigenesis will eventually involve all of the external and internal factors previously mentioned
• body cells resolve into three main types:

  1. cells that never divide during the lifetime of an organism (terminally differentiated)
  2. cells that retain the ability to divide, but ordinarily do not (in G0 phase)
  3. cells that routinely divide and can alter the rate of division (stem cells)
• in what phase does DNA replicate?


  the S (synthesis) phase
• what does G1 phase stand for?


  growth, or gap, phase
• what are the characteristics of the G1 phase?

  • high rate of metabolism
  • protein synthesis
  • vigorous growth
  • most organelles are duplicated
  • centriole replication begins
• what occurs in the S phase?

  • DNA replication
  • synthesis of new histones
  • assembly of new chromatin
• what occurs in the G2 phase?

  • synthesis of enzymes and proteins essential for cell division
  • transport of said enzymes and proteins to their final sites
  • the completion of the replication of centrioles
• what happens in the M phase?

  • mitosis
  • splitting of the genome
• extracellular mitogenic and growth-stimulatory factors usually provide the external signals for a cell to divide
• what does mitogenic mean?


  producing, or stimulating, mitosis
• growth factors bind to a membrane-receptor specific to it, which triggers a signalling cascade in the cytosol
• phosphorylation activates proteins and transfers a signal to the nucleus
• what happens when phosphorylation helps transfer a signal to the nucleus?


  in the nucleus, phosphorylation events activate transcription factors that bind to promoters and enhancers in the DNA
• what happens as a result of transcription factors binding to promoters and enhancers in the DNA?


  their associated genes are turned on
• some of the genes turned on by downstream transcription factors encode cyclins, which prepare the cell to undergo mitosis
• what are cyclins?

  a family of proteins that control the progression of a cell through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes, or a group of enzymes required for synthesis of cell cycle
• what does MAPK stand for?

  mitogen-activated protein kinase
• what do MAPKs do?

  convert extracellular stimuli into a wide range of cellular responses
• what kind of kinases are MAPKs?

  protein Ser/Thr kinases
• MAPK enzymes also attach phosphate groups to other proteins
• what is the order of the cell cycle?


  G1, S, G2, and M
• what is the order of the phases in the cell cycle?

  1. interphase (chromosomes are indistinguishable)
  2. prophase (chromatids pair up)
  3. metaphase (chromosomes move to the middle of the spindle)
  4. anaphase (chromosomes are pulled apart)
  5. telophase (two daughter chromosomes, twin nuclei created)
• which overall phase are the G1, S, and G2 phases a part of?


  interphase
• 1. interphase
  2. mitosis
  3. cytokinesis
• what are the 3 critical points for dividing cells?

  1. G1/S (start or restriction) checkpoint
  2. G2/M checkpoint
  3. M/G1 checkpoint
• what is another term for a checkpoint?

  boundary
• what is a chromatid?


  one of the two identical halves of a chromosome that has been replicated in preparation for cell division
• what is a chromosome?


  a DNA molecule that has all or part of the genetic material of an organism
• what is a chromatid?

  one half of a newly copied chromosome
• what does a chromosome consist of?

  a single, double-stranded DNA molecule
• at the G1 checkpoint, cells decide whether or not to proceed with division based on the following factors:

  • cell size
  • nutrients
  • growth factors
• G1/S boundary when the cell is committed to DNA synthesis
• G2/M boundary when the cell is committed to mitosis
• M/G1 boundary when the cell is commited to chromosome separation