Cell Growth and Division

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Cell Growth and Division

• Division or reproduction is a way of passing on
  the genetic code or DNA of a species from parent
  to offspring.

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Cell Reproduction

• Why do cells divide?
• Growth-increase in body size.
• Cell renewal and replacement,
• Ex cuts are healed, red blood cells replaced.
• New individual (clone) asexual reproduction

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Types of Cell Division

• Mitosis-
• Growth of an organism
• creation of a genetically identical offspring
  (Asexual)
• Meiosis- A new genetically different individual
  is created (sexual)

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The Cell Cycle (Eukaryotic)

• Cell Cycle
• Series of events the cell goes through as it
  grows, Replicates DNA and divides to produce two
  identical cells (daughter cells)
• Four main stages
• Gap 1
• Synthesis
• Gap 2
• Mitosis

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• Interphase (Gap 1, synthesis, Gap 2)
• Three phases cell spends most of its time in
• First growth phase G1
• - Cell growth and normal function, organelles
  increase in number.
• Cell spends most of its time in this phase,
  varies for different cells
• Divide if ready and given a signal to
  (checkpoint)
• Synthesis phase S
• - DNA is copied, (chromosome replication) forms a
  chromatid which is two chromosomes joined by the
  centromere

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• Second growth phase G2
• - Normal function
• - Preparation for the nucleus to divide
  (checkpoint)
• - Organelles such as microtubes are formed which
  are needed for division
• Mitosis (M)
• Mitosis
• Division of the Nucleus
• Nuclear envelope dissolves
• Cytokinesis
• Division of the cytoplasm
• Formation of two new genetically identical
  daughter cells

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• Cells divide at different rates
• Q. Which divide faster prokaryotic or eukaryotic
  cells?
• Rate is linked to need, Ex an embryos cell
  division rate is faster than an adult
• G1 varies the most
• Q. Why does the lining of your stomach get
  replaced every few days?
• G0 unlikely for a cell to divide Ex neurons,
  white blood cells
• Q. Do you think a skin cell would have a long or
  short G1 stage?

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Limits to Cell Growth

• Question Is the growth of an organism due to the
  size of its cells or the number of cells?
• Number
• 25 million cell divisions a second in the human
  body.
• Question Cells grow until they reach a certain
  size then divide, why?

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Answer Cell size is limited pg 136

• Surface area to volume ratio of a cell is
  important
• The volume can not get to large as the surface
  area of the cell will not be able to sustain the
  cells needs.
• Q. Look at the table which cell has the greatest
  surface area? Which cell has the greatest surface
  area to volume ratio?
• Exchange of materials
• If cell is too large not enough substances can
  enter and leave the cell to meet its needs

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• What is the volume/contents of the cell?
• Cytoplasm and all its organelles
• What is the surface area of the cell?
• Cell membrane
• What are the needs of the cell?
• Water, oxygen, glucose, wastes

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• Vocabulary
• Chromosome condensed DNA and proteins
• Histones proteins DNA wraps around
• Chromatin loose combination of DNA and proteins
• Chromatid one duplicate chromosome
• Sister Chromatid two duplicate chromosomes
• Centromere joins sister chromadids together
• Telomere ends of chromosomes that do not carry
  genes

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Regulation of the Cell Cycle

• External Regulators
• Respond to signals from outside the cell, from
  other near by cells or hormones from other parts
  of the body
• Physical cell to cell contact
• Growth factors many different proteins that
  stimulate cell growth in different cells
• Hormones Human growth hormone from the anterior
  pituitary gland stimulates cell division in bone
  cells

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• Internal Regulators
• Respond to what is going on inside the cell
• Ex proteins known as cyclins (activate kinases)
  and kinases (enzyme controls cell cycle)
• Makes sure all phase are completed before cell
  moves on to the next phase these are known as
  checkpoints
• Apoptosis programmed cell death

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• Cancer uncontrolled cell division
• Cells lose the ability to control their growth
  (cell cycle)
• Do not respond to signals from the cell
• Many of them have damaged genes p53 which help
  with stopping cell growth or oncogenes
  (accelerate growth)
• Damage surrounding tissues
• Tumor disorganized clump of cancer cells which
  do not perform the functions of the normal cells
  around them
• Benign usually a harmless clump that can be
  removed
• Malignant Cancer cells break away and go to
  other parts of the body (metastasize)

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• Causes (Vary)
• Known as Carcinogens
• Smoking and air pollutants, Ex lung cancer
• Virus, Ex cervical cancer
• Exposure to radiation and other harmful
  chemicals, Ex skin cancer UV light
• Inherited Some types of breast cancer

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