Cell Growth and Division

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Cell Growth and Division

• Chapter 10(M)

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Limits to Cell Size

• Cells grow and increase in size
• Upper limit to the size of a single cell
• If cells keep growing
• More demands are placed on the DNA
• Cells becomes less efficient in moving nutrients
  and wastes
• Cells divide before it becomes too large

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Cell Size

• As a cell increases in size its volume increases
  faster than its surface area.
• Smaller objects have a greater ratio of surface
  area to volume.

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Purpose of Cell Division

• Cell division ? essential for life
• Repair? replacement of lost or damaged cells
• Skin cells are constantly being replaced
• Growth? cells divide and increase in size, so
  that organism can grow
• To maintain a favorable Surface area to volume
  ratio
• Infant? Baby? Child? Adult

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Cell Division and Reproduction

• Asexual Reproduction
• Sexual Reproduction

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Asexual Reproduction

• Production of offspring from a single parent
• Offspring is identical to parent
• Ex bacteria, yeast, unicellular organisms some
  multicellular organisms

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Binary Fission? Bacteria
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Budding? Yeast
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Sexual Reproduction

• Two parents are involved
• Genetic material from each parent combines
• Offspring is different from parent

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The Process of Cell Division

• Genetic material - packaged as DNA is distributed
  to two daughter cells

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Chromosomes and Cell Division

1. Chromatin? fibers of DNA and protein
2. Chromosomes? Chromatin fibers condense and become
   visible compact structures
3. Sister Chromatids? before the cell divides the
   DNA duplicates and forms identical copies

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Prokaryotes and Eukaryotes

• Prokaryotes, the genome is often a single long
  DNA molecule
• Eukaryotes, the genome consists of several DNA
  molecules
• DNA is passed from one generation to the next

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The Cell Cycle

• An orderly sequence of events that extends from
  the birth of a cell till the time it divides
  itself
• All Eukaryotic cells undergo this cycle
• Cycle is divided into
• Interphase
• Mitotic Phase

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The Cell Cycle
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Interphase? 90 of the Cell Cycle

• G1(gap)phase cell spends most of its functional
  life.
• Gap bet. DNA syn cell div
• Cell grows, protein organelles synthesized

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Interphase? 90 of the Cell Cycle

• G1(gap)phase cell spends most of its functional
  life.
• Gap bet. DNA syn cell div
• Cell grows, protein organelles synthesized

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Interphase contd.

• S-Phase ?the DNA synthesis phase.
• DNA molecules are copied or replicated, single
  stranded DNA in G1 phase to double stranded DNA
  in G2.
• G2 Phase? completion of DNA syn. onset of cell
  division

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Mitotic Phase

• Division of the nucleus plus cytokinesis, ?
  produces two identical daughter cells
• Interphase is not part of mitosis, it encompasses
  stages G1, S, and G2 of the cell cycle.

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Interphase

• Chromatin not visible
• DNA replicated
• New organelles are formed
• Cell grows by producing proteins and cytoplasmic
  organelles
• Prepares for cell division.

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Mitosis

• Division of the Nucleus
• Stages
• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase

• Chromosomes condensed and visible with sister
  chromatids joined together
• The nucleoli disappear
• Centrioles at opposite poles of cell
• The mitotic spindle begins to form
• Phase ends with the breakdown of the nuclear
  membrane

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Metaphase

• The second stage
• Chromosomes gather in the a plate across the
  middle of the cell
• Mitotic spindle is fully formed
• All chromosomes are attached to the spindle
  microtubules

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Anaphase

• The third stage of mitosis
• The sister chromatids suddenly separate from
  their partners.
• Each chromatid ? daughter chromosomes move toward
  the poles
• Microtubules shorten, bringing the chromosomes
  closer to the poles.

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Telophase

• The final stage of mitosis
• The chromosomes reach the poles of the spindle.
• The reverse of prophase? spindle disappears,
  nuclear envelopes reform, the chromosomes uncoil
  and lengthen, and nucleoli reappear.
• Two genetically identical daughter nuclei are
  formed
• Cytokinesis follows

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Cytokinesis

• Division of the cytoplasm
• Occurs along with telophase
• Two daughter cells separate
• Difference in animal and plant cells
• Animal Cell ?cell membrane pinches off to form a
  cleavage furrow
• Plant Cell ?Cell plate is formed to divide cell
  into two

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Animal Cell
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Plant Cell
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Regulating the Cell Cycle

• Cell division is affected by
• Cell Density
• Anchorage
• Regulatory Proteins

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Density dependent inhibition

• Cultured cells normally divide until they form
  a single layer on the inner surface of the
  culture container
• If a gap is created, the cells will grow to fill
  the gap.

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Anchorage dependence

• Cells must be anchored to a substratum, typically
  the extracellular matrix of a tissue.
• Cancer cells are free of both density-dependent
  inhibition and anchorage dependence.

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Regulatory Proteins

• Cyclins? timing of the cell cycle
• Regulatory proteins
• Internal
• External ? growth factors
• Fluctuates during cell cycle

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Growth Factors

• Coordination between cells
• protein signals released by body cells that
  stimulate other cells to divide
• Body has many different types
• Each stimulates only cells with that type of
  receptor

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Apoptosis

• Programmed cell death
• Apoptotic cells shrink in size, break into
  smaller pieces called apoptotic bodies that other
  body cells recognize and eat.

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What Causes Cancer?

• Cells do not have a properly functioning cell
  cycle control system
• Cells divide excessively and result in an
  abnormal mass of cells
• tumor-suppressor genes ? gene p53
• inhibits cell division
• if switched OFF can cause cancer

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Growth Factors and Cancer

• Growth factors can create cancers
• proto-oncogenes
• normal growth factor genes that become oncogenes
  (cancer-causing) when mutated
• stimulates cell growth
• if switched ON can cause cancer
• example RAS (activates cyclins)
• tumor-suppressor genes
• inhibits cell division
• if switched OFF can cause cancer
• example p53

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Tumors and Cancer

• Benign? mass of normal cells
• Can be removed surgically
• Always remain at their original site
• Malignant
• Mass of cancer cells
• Spread to other tissues by entering the
  circulatory system
• Metastasis ? spread of cancer cells beyond site

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Types of Cancer

• Carcinoma ? external or internal coverings of the
  body-skin, intestinal linings
• Sarcoma? bone and muscle
• Leukemia and Lymphoma- blood forming tissues

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Treatment of Cancer

• Surgery
• Radiation therapy? high energy radiation disrupts
  cell division
• Chemotherapy? drugs that inhibit cell division
• Side effects
• Radiation can lead to sterility
• Chemotherapy can cause nausea, hair loss