Cell Growth

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Cell Growth Division

• Ch. 10

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• Cells divide to maintain a workable ratio of
  volume to surface area.  The original cell is
  called the parent cell and the offspring are
  called daughter cells.  The offspring receive a
  portion of the cytoplasm, organelles, and
  hereditary information from the parent. 
• Cell size

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Limits to Cell Growth

• 1.  DNA overload - more demands are placed on the
  cells DNA2.  Material Exchange - the rate at
  which food oxygen are used up waste products
  are produced become too much for the cell3. 
  Ratio of Surface Area to Volume - volume
  increases more rapidly that surface area4.  Cell
  Division - 2 new daughter cells form

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Diploid Cells

• Diploid cells are also known as 2n because they
  have the full set of chromosomes.  Somatic cells
  are diploid.  The diploid number for humans is
  46.

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Haploid Cells

• Haploid cells are also known as n because they
  have half of the cells found in a typical somatic
  cell.  The haploid number for humans is 23.  An
  example of a haploid cell in humans would be
  sperm or eggs. 

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Diploid vs. Haploid Division

• Diploid cells undergo cell division known as
  mitosis while haploid cells undergo cell division
  known as meiosis.  All cells that undergo mitosis
  have daughter cells with the same number of
  chromosomes as the parent cell, while cells that
  undergo meiosis have half the number of
  chromosomes as the parent cell. 

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Homologous Chromosomes

• Every body cell contains 2 chromosomes bearing
  genes for the same set of characteristics, the
  2 members usually have the same size shape. 
  The members of a pair are called homologous
  chromosomes one from the mother one from the
  father.
• A locus is a particular site on a chromosome.

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Chromosome drawing
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Human Karyotype
Autosomes 1st 22 pairs of chromosomes Sex
chromosomes last pair determines sex samples
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Karyotype

• Nondisjunction - failure of chromosomes to
  separate properly in cell division responsible
  for Klinefelter Syndrome (XXY) , Turner Syndrome
  (XO), Trisomy-21 (Down Syndrome)

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Cell Division

• Some cells divide once a day, others are not as
  frequent. Brain cells and other highly
  specialized cells (mature muscle cells) dont
  divide at all.

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THE CELL CYCLE

• 1. Interphase - time in between divisions cell
  carries on its usual life activities- metabolism
  is very high in this stage
• 3 Stages of Interphase  1) G1 - growth phase
  the cell decides if it will divide again
  cellular differentiation occurs2) S - DNA
  replication occurs chromosomes go from being
  single to being double (2 sister chromatids)3)
  G2 - another growth phase organelles reproduce
  prepares for division.

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The Cell Cycle
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Cell Cycle

• 1) Interphase 90 of cells life
• 2) Mitotic Stage broken up into
• a) Mitosis splits nucleus contents
  consists of prophase, metaphase, anaphase,
  telophase
• b) Cytokinesis splits cytoplasm

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Prophase

• Prophase - EARLY centrioles begin to migrate
  to opposite sides of the nucleus, chromatin may
  become denser, MIDDLE nuclear membrane starts
  to break down, nucleolus begins to disasppear,
  chromosomes appear, centrioles migrate to poles
  produce the aster complex that makes the spindle
  arising from 2 centrosomes, LATE no nucleolus
  or nuclear membrane, chromosomes are floating
  within the cell, spindle apparatus has formed

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Metaphase

• Metaphase - chromosomes align themselves along
  the equator they are attached to the spindle
  fibers at the kinetochore.

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Anaphase

• Anaphase - splitting of the centromeres , spindle
  fibers contract chromatids are divided, these
  become chromosomes are pulled to the poles, the
  chromosomes are V-shaped in middle anaphase
  J-shaped in late anaphase, this stage is over
  when chromosomes reach the poles.

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Telophase

• Telophase - this is the reverse of prophase,
  MIDDLE begins the formation of the nuclear
  membrane, the nucleolus reappears, granular
  chromatin reappears, LATE there is a complete
  nuclear membrane, the aster complex disappears,
  centrioles disappear

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CYTOKINESIS

• The result of cell division is the production of
  2 identical daughter cells.  In animals a
  cleavage furrow occurs that pinches in the cell. 
  This begins during anaphase.  In plants a cell
  plate forms in the middle of the dividing cell
  this eventually forms the cell wall after
  migrating to the edges of the cell.

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Examples
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MEIOSIS

• Meiosis occurs in sex cells.  It is composed of 2
  stages  Meiosis I Meiosis II.  Meiosis
  consists of 2 nuclear divisions in which the
  chromosomes divide only once.  The result is that
  mature gametes have only 1 member of each
  homologous chromosome pair (haploid).  When the
  gametes unite, a zygote is formed. 

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MEIOSIS I

• 1.  Prophase I  -the 2 members of each pair of
  homologous chromosomes come into side-by-side
  contact .  Each chromosome has already replicated
  to form 2 chromatids, each of which will become a
  new chromosome.  The 2 chromatids are joined at 1
  point, the synapsis, so that each will become 4
  future chromosomes, is thus called a tetrad. 
  In this stage, crossing over occurs in which
  chromatids exchange segments (increases genetic
  variation).

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Metaphase I

• 2.  Metaphase I - the chromosomes align on the
  equator of the cell

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Anaphase I

• 3.  Anaphase I - unlike mitosis, the centromeres
  holding the chromatids together do NOT divide
  each chromatid is pulled toward each pole (1st
  Reductive Division occurs)

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Telophase I

• 4. Telophase I - the daughter cells contain 1 of
  each of the homologous chromosomes  - total
  chromosome number is now 23 in humans.

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Meiosis I
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Meiosis II
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MEIOSIS II

• The second meiotic division more closely
  resembles the events in mitosis.  The chromosomes
  are split at the beginning of meiosis II by
  division of the centromeres, single-stranded
  chromosomes move toward each pole.  Each
  chromatid now exists in a separate cell.  The
  essential difference is that you start with
  haploid cells. 4 cells are now formed.  In the
  male, all 4 cells are functional sperm, but in
  the female, only 1 is functional the others
  become polar bodies. 

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Oogenesis
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Spermatogenesis
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Comparing Mitosis Meiosis

• Similarities Both are types of cell division
  Chromosomes duplicate only once
• Differences Mitosis used for somatic cells,
  meiosis used for sex cells Mitosis yields 2
  diploid genetically identical cells, meiosis
  yields 4 haploid genetically different cells
  Mitosis has 1 division of the nucleus, meiosis
  has 2

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Cell Differentiation

• All cells contain the same DNA.  In cell
  differentiation, some of the DNA is repressed and
  some is expressed.  This allows cells to have
  different functions. 

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Cell Differentiation Regulation

• Stem cells Unspecialized cells that can
  differentiate into any type of body cell 2
  types are embryonic adult
• Apoptosis programmed cellular death (all cells
  have a pre-determined life span)

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Cell cycle regulators

• 1.  Internal regulators - proteins respond to
  events inside the cell to determine when mitosis
  occurs cyclins bind to cyclin-dependent
  kinases that start stages in the cell cycle2. 
  External regulators - proteins respond to events
  outside the cell direct cell to speed up or
  slow down the cell cycle cells grow until they
  touch each other

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Types of Cell Regulation

• Density-dependent inhibition cells stop
  dividing when they touch each other based on
  cell surface proteins (will close wounds)
• Anchorage dependence cells must be in contact
  with a solid surface (matrix of tissue) to divide

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Cancerous Division

• Tumor abnormally growing mass of cells
• Benign stays enclosed in a wall remains at
  the original site
• Malignant spreads into neighboring tissues
  causes angiogenesis (lures new blood vessel
  formation)
• Metastasis spread of cancer through the body
  via the circulatory/lymphatic system

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Types of cancers

• Carcinomas in coverings of skin/lining of
  intestines
• Sarcomas in bone, muscle in areas that
  support the body
• Leukemias /lymphomas in blood-forming tissues
  (marrow, spleen, lymph nodes)
• Most chemotherapy agents work to freeze or
  prevent spindle formation.

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Cancer Development

• Hypertrophy - cells increase in sizeHyperplasia
  - cells increase in numberDysplasia - cells
  change their shape (atypical cells) Neoplasia -
  producing new cellsApoptosis - is programmed
  cellular death

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Asexual vs. sexual reproduction

• Asexual reproduction only takes one parent.
  Asexual reproduction is the primary form of
  reproduction for unicellular organisms. Asexual
  reproduction is relatively rare among
  multicellular organisms.

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• While asexual reproduction may have short term
  benefits when rapid population growth is
  important or in stable environments, sexual
  reproduction offers a net advantage by allowing
  more diversity, allowing adaptation to changing
  environments.

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Types of asexual reproduction

• 1. Budding - the formation of a new organism by
  the protrusion of part of another organism.
  This is very common in plants, bacteria, and
  fungi, but may be found in animal organisms, such
  as the hydra, as well.

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• 2. Binary fission - in single-celled organisms by
  which one cell divides into two cells of the same
  size, used by most bacteria. This process results
  in the reproduction of a living cell by division
  into two equal or near-equal parts.

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• 3. Vegetative propagation - Plants are produced
  using material from a single parent and as such
  there is no exchange of genetic material,
  therefore vegetative propagation methods almost
  always produce plants that are identical to the
  parent. Vegetative reproduction uses vegetative
  plants parts or roots, stems and leaves.

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• 4. Spore formation alternation of generations
  allows spore formation with meiosis (not true
  asexual method), some fungi algae, however, can
  form spores without meiosis

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• 5. Fragmentation new organism grows from a
  fragment of the parent (regeneration)

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• 6. Parthenogenesis - form of reproduction found
  in females where growth and development of an
  embryo or seed occurs without fertilization by
  males (plants, bees, aphids, wasps, some
  reptiles, some fish, some amphibians).

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Sexual reproduction

• 1. Conjugation - transmission of DNA without
  fusion of gametes (some bacteria protists)

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• 2. Fertilization - sperm egg (gametes) join to
  form embryo