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Mitosis Powered By Docstoc
					Cell Growth and Reproduction

  How a Parent cell divides to form
       2 new Daughter cells
                                Cell Growth
• As an organism grows, do its cells increase in
  size OR do cells divide to produce new
  daughter cells?
• 2 limits to Cell Growth (increase in size)
   – More demands cell places on its DNA (to
     produce enough proteins in adequate
     amounts at right place at right time)
   – More difficulty controlling the trafficking of
     nutrients/wastes into and out of cells
                     DNA “Overload”
• When cell is small, information stored
  within DNA able to meet its needs
• As cell increases in size, no extra copies
  of DNA produced
• Therefore, if cell grows without limits, a
  “information crisis” would result
           Trafficking of Materials
• Rate of exchange of materials is
  affected by surface area of cell (or total
  area of its cell membrane)
• YET, Rate at which nutrients
  used/waste products produced
  dependent upon cell’s volume
           Trafficking of Materials
• Thought experiment:
    • Cell is shaped like a cube
    • If length = 1 cm; SA = 6 cm2 (L x W x # sides)
    • THEREFORE, volume = 1 cm3 (L x W x H/D)
    • RATIO SA/V = 6:1

    • If length = 2 cm; SA = 24 cm2
    • Volume = 8 cm3
    • Ratio SA/V = 3:1
              Trafficking of Nutrients
• NOW, Length = 3 cm; SA = ? cm
• Volume = ?
• Ratio SA/V = ?

• Length = 4 cm; SA ? Volume ? Ratio ?

• TREND is: Volume is increasing at a faster rate, as
  compared to the Surface Area of the cell (ratio is
  decreasing); SOLUTION?
Surface Area:Volume Ratio
Graphic Representation-Ratio
                          Final Problem
• If cell size doubles (from 1 cm in size to 2
  cm), the cell requires 8x more nutrients and
  would have 8x more waste to excrete
• YET, only have a 4x increase in SA; the
  plasma membrane does not have enough SA
  through which materials can diffuse
• Cells either starve to death or become
  poisoned from buildup of waste products
                              Cell Division
• Before cell becomes too large, it MUST divide
  to form 2 “daughter cells”
• Before cell division occurs, the cell
  replicates/copies its DNA.
• WHY? (2 reasons)
• Goal: to produce 2 daughter cells identical to
  the parent cell
• Direction: to grow in size AND to replace
  dead/old/worn out/damaged cells
• DNA is carried within
  chromosomes (DNA + proteins)
• Each organism has a specific
  number of chromosomes in
  each cell (Fruit fly = 8, Human
  = 46, Cat = 38 and Mouse = 40)
• Chromosomes only become
  visible at the beginning of cell
            Chromosomes (cont’d)
• Terminology:
    • At the start of cell division, each chromosome
      doubles to form TWO SISTER CHROMATIDS
    • Each pair of sister chromatids are attached at
      an area referred to as a CENTROMERE; usually
      attachment site is near the center of the sister
      chromatid pair
    • Therefore, each human cell is composed of 46
      chromosomes, each of which consists of a pair
      of sister chromatids
                       The Cell Cycle
• A series of events cells proceed through
  as they grow and develop
• Interphase- the “in-between” period of
  growth from round of mitosis to the
• During the cell cycle, cell grows,
  prepares for cell division and divides to
  form two daughter cells
The Cell Cycle
                         The Cell Cycle
• 4 phases of cell division:
  – M phase- Mitosis/Cytokinesis (shortest
  – G1 Phase = Gap 1; all the events that
    occur as a cell prepares to copy its
  – S phase- Chromosome copying
  – G2 = Gap 2; all the preparation for
    Mitosis/Cytokinesis + Centrioles double
      Student Review Questions

• What is a chromosome?
• What is a centromere?
• What are sister chromatids?

• What are the 4 parts of the Cell Cycle?
• What occurs in each step?
Mitosis-(Nuclear Division) -
            • Each chromosome
              doubles to form 2 sister
            • Each centriole doubles
              as well
            • Chromatin- DNA
              wrapped around
              proteins; Diffuse
              material within nucleus
            • Cell increases in size
            • Cellular activities for life
              occur here
        • 50-60% of total time
        • Chromosomes
        • Nuclear membrane

        • Centrioles separate
          to opposite
          poles/ends of cell
        • Microtubules extend
          from the centrioles
          to form ASTER-
          structure located at
          poles of cell

        • Other Microtubule
          fibers go from
          pole to pole
          forming a
          structure =
         • Chromosomes line
           up across the
           Metaphase plate
         • Microtubules/spindle
           fibers connect the
           centromeres of each
           chromatid pair to
           the centrioles at the
           “poles” of the cell
        • Sister chromatids
          separate to opposite
          poles of the cell
        • The centromere of each
          pair of chromatids
          divides, separating into
          individual chromosomes
        • Centrioles “reel in” each
          member of the sister
          chromatid pair by
          shortening the spindle
         • Nuclear membrane
           reforms around
         • Chromosomes de-
           condense forming
         • Spindle fibers
           disappear; nucleolus
Cytokinesis-Cytoplasm Division

               • Cell membrane
                 invaginates (drawn
                 inward) until the
                 cytoplasm is pinched
                 into 2 equal parts
               • Each part contains a
                 nucleus and organelles
               • Plant cells: cell plate
                 forms; midway between
                 dividing nuclei
                  Results of Mitosis

• In both animal and plant cells, Mitosis
  results in the formation of two daughter
  cells identical to each other and to the
  parent cell which they came from
• The resulting daughter cells enter
      Student Review Questions

• What is the goal of Mitosis?
• Briefly describe the events that occur
  during each step of Mitosis:
  – Interphase            Anaphase
  – Prophase              Telophase
  – Metaphase             Cytokinesis
      Length of Time for Mitosis

• Length of time needed for cell to divide
  completely depends on:
  – the kind of cell
  – the environmental conditions under which
    it exists
  – Most cells complete mitosis in 1-2 hours
  – Mammalian cells grown in a laboratory may
    require 24 hours to complete one cell
 • Cell prepares for
   division by:
          replicating
           DNA and
          increasing
           cell size
• Nuclear membrane
  /nucleolus disappears
• Chromatin/
  chromosomes condense
• Spindle fibers/MT
  elongate from migrating
  “anchor proteins”
 • aligning
   chromosomes at cell
 • attaching spindle
   fibers from each
   new daughter cell
   pole to each
   chromosome at the
• spindle fibers pull
  chromosomes apart
• one-half of each
  (chromatid) moves
  to a new daughter
 • DNA decondenses
   and two nuclei form
 • new cell wall (cell
   plate) appears
   between the two
   nuclei to form two
   new daughter cells
  • Cell plate forms
    midway between
    divided nuclei
  • Cell plate gradually
    develops into
  • Cell wall forms
    within cell plate
                  Cell Cycle Regulation
• Different cell types grow and divide at varying rates
  (muscle and nerve cells infrequently vs. skin and
  digestive tract constantly throughout life)
• Controls : contact inhibition
   – Cyclin proteins-regulate timing of cell cycle
   – Cyclin-dependent Kinases (cdk) (adds phosphate
     to a protein), along with cyclins, are major control
     switches for the cell cycle, causing the cell to
     move from G1 to S or G2 to M.
   – cdk inhibitors(cdk-I)- remove phosphate
     group/switch off cell cycle progression
 Cell Cycle Regulators (cont’d)

• Internal regulators- proteins that
  respond to internal/within cell signals
• External - respond to external/outside
  cell signals; speed up or slow down rate
  of mitosis (oncogenes/tumor suppressor
  genes-the “accelerators and brakes” )
Cell Cycle Regulators
                  Cell Cycle Regulation

• MPF (Maturation Promoting Factor) includes the CdK
  and cyclins that triggers progression through the cell
• p27 is a protein that binds to cyclin and cdk blocking
  entry into S phase. Recent research ( Nature Medicine
  3, 152 (1997)) suggests that breast cancer prognosis
  is determined by p27 levels. Reduced levels of p27
  predict a poor outcome for breast cancer patients.
         P53-The “Guardian of the
• p53 is a protein that functions to block the cell cycle
  if the DNA is damaged. If the damage is severe this
  protein can cause apoptosis (cell death).
          – p53 levels are increased in damaged cells.
            This allows time to repair DNA by blocking
            the cell cycle.
          – A p53 mutation is the most frequent
            mutation leading to cancer. An extreme
            case of this is Li Fraumeni syndrome, where
            a genetic defect in p53 leads to a high
            frequency of cancer in affected individuals
     Normal Cell Characteristics

        Reproduce themselves exactly
 Stop reproducing at the right time
 Stick together in the right place
 Self destruct if they are damaged
 Become specialized or 'mature'
• Uncontrolled cell growth
• Gene- segment of DNA
  that controls the
  production of a protein
• Changes in one or more
  genes that produce
  enzymes (proteins!)
  involved in control of
  cell cycle
How Cancer Cells are different
         They carry on reproducing
 They don't obey signals from other
  neighboring cells
 They don't stick together
 They don't become specialized, but stay
 They don't die if they move to another part of
  the body
They don’t stop reproducing
                     Cancer (cont’d)

• Characteristics include: lack of contact
  inhibition, “pile on”/cell growth and
  ability to grow in suspension
• Cancer cells do not respond to signals
  regulating cell growth; tumor formation
  results (masses of cells that damage
  surrounding tissues; deprive normal
  cells of nutrients)
Cancer cells do not stick together
                     Cancer (cont’d)

• Tumor types: benign vs. malignant
• Tumor metastasis
• Second leading cause of death in U.S.
  (behind Cardiovascular disease)
• Nearly half of all men and over one
  third of all women will develop cancer
  during their lifetime
Tumor Metastasis
                       Cancer (cont’d)
• Most prevalent: in females breast and ovarian
  vs. Males-prostate, testicular and colon;
• These abnormal and cancerous cells develop
  because of damage to DNA that cannot be
  repaired. Sometimes the cancer is inherited
  through the DNA but more often the damage
  to the DNA is caused by exposure to
  something in the environment.
              Cancer -Risk Factors

• combination of genetics/family history
  and environmental exposure
• YOUR GENES- > 50% of all cancers have a
 defect in p53- a tumor suppressor protein
• radiation exposure (UV, X-rays,
  microwaves), viruses, tobacco, air and
  water pollution
• THINK: Domino Effect!
  Carcinogens/Risk Factors

• changes in the body which then leads
  to the development of cancer
• Hormone levels
• asbestos (and other fine particulate
  matter), nickel compounds, arsenic,
  benzene and solar radiation
 Common Risk Factors
 Growing older
 Tobacco
 Sunlight
 Ionizing radiation
 Certain chemicals and other substances
 Some viruses and bacteria
 Certain hormones
 Family history of cancer
 Alcohol
 Poor diet, lack of physical activity, or being overweight
                   Some Thoughts on Cancer

• Not everything causes cancer.
• Cancer is not caused by an injury, such as a bump or bruise.
  Cancer is not contagious.
• Although being infected with certain viruses or bacteria may
  increase the risk of some types of cancer, no one can "catch"
  cancer from another person.
• Having one or more risk factors does not mean that you will get
  cancer. Most people who have risk factors never develop
•   Some people are more sensitive than others to the known risk
Cancer in the Scalp
Chest X-Ray-Lung Cancer
• unexplained weight loss
• Developing a fever; disease or the treatment
  can affect the immune system and inhibit its
  ability to resist infection
• Fatigue
• unexplained pain
• Skin changes darkening, yellowing (jaundice),
  reddening, itching or even excessive hair
           Cancer-Early Detection

• The sooner the cancer is detected and
  treated, the better an individual’s
  chance of making a full recovery
• A person’s chance of detecting the
  cancer early is greatly improved if you
  incur regular physicals and undertake
  regular self examinations
               Cancer-Early Detection
• Self examinations for the breast
• Physical examinations by a doctor or other health
  professional for the breast, colon, thyroid and skin,
• Laboratory tests like a Pap test, prostate specific
  antigen (PSA) blood test and mammography
• Most effective strategy for early detection is to use a
  combination of two or more early detection
                Cancer -Prevention

• eating healthy and maintaining a
  nutritional diet by limiting your
  consumption of fried foods, alcohol, and
  refined carbohydrates
• choose white meat over red meat and
  eat whole grain foods rather than
  processed ones.
               Cancer -Prevention

• It also helps to be physically fit by
  exercising at least an hour a day and
  walking as much as you can or joining a
                 Cancer -Prevention

• exercise + healthy lifestyle (diet) + DO NOT
• Diet: low in fat and high in fiber content
  (fruits, vegetables, grain products)
• Vitamins and minerals (A, C, E, Calcium and
  carotenoids-in orange and yellow vegetables)
• Used to treat metastasized cancer cells
• Can be used to cure cancer, to prevent it
  from spreading, to slow the growth of the
  cancer, to destroy cancerous cells that have
  moved to other parts of the body and to help
  relieve some of the symptoms caused by the
• Purpose will actually serve all depends on
  the type of cancer you have and its stage of
                Radiation Treatment
• uses ionizing radiation to kill cancer cells and
  reduce the size of tumors.
• Works by destroying the cells in the area that
  is being targeting by injuring their genetic
  material, thereby making it impossible for
  them to grow and divide
• tries to damage as many, if not all, of the
  cancer cells as possible while limited the
  harm to the nearby healthy cells and tissue.
• Immune system (body’s natural defense mechanism)
  is an important element in the body’s response to
• Some forms of cancer develop when the immune
  system is not able to destroy the cancerous cells or
  inhibit their growth.
• work in a couple of ways such as interfering with the
  growth of the cancer cells, indirectly helping the
  healthy immune cells to control the cancer or
  repairing normal cells that were damaged by the
  cancer treatment.
                      Surgery Treatment
• It can cure the cancer if the cancer can be
  completely removed, if a border of healthy tissue that
  is cancer cell free can also be removed with the
  cancer and if the cancer has not spread before the
• During the surgery, the main lymphatic nodes and
  lymph nodes that are closest to the cancer or the
  organ where the cancer cells are allocated will be
  removed;these are the places where the cancer is
  most likely to have spread
• Post Chemo./Radiation usually prescribed
               Papilloma Virus and Cancer

 Two human papilloma viruses that infect the
  reproductive organs (sexually transmitted disease)
 “Pediatricians, gynecologists and even health insurers
  all call Gardasil (Merck and Co.), the first vaccine to
  prevent cervical cancer, a big medical advance.” Yet,
  “get state legislatures to require 11- and 12-year-old
  girls to get the three-dose vaccine as a requirement
  for school attendance?” AND “Promote sexual
 Vaccines mandated for school attendance “usually
  are for diseases easily spread through casual contact,
  such as measles and mumps.”
                      Viruses and Cancer
 Hepatitis B and Hepatitis C viruses, which infect
  the liver and are closely associated with liver cancer
  (probably because of the chronic inflammation they
 Some herpes viruses such as the Epstein-Barr
  virus (implicated in Burkitt's lymphoma) and KSHV
  that is associated with Kaposi's sarcoma (a
  malignancy frequently seen in the late stages of
 two human T-cell leukemia viruses, HTLV-1 and
• Remember: To get Cancer, many dominoes
  have to fall!
• Prevention is Key
   – Diet
   – Exercise
   – Yearly check-ups + self examination

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