Why cant organisms just be one giant cell''

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Why cant organisms just be one giant cell?..

• 1. Diffusion cannot occur quickly and efficiently
  if the distances involved become too large.
• wastes would collect inside the cell and
  poison it
• nutrients could not reach organelles in
  time, so cells would die
• 2. Information overload would occur
• DNA does not make copies as a cell grows
  what it starts with is all that it has
• Must be enough DNA blueprint to
  allow for protein production

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Functions of Cell Division

• Reproduction of cells
• all cells come from pre-existing cells
• results in two identical cells except for
  size
• Growth and Development
• cells grow in size just like tadpoles become
  frogs
• Tissue renewal
• skin cells are being replaced, cuts and
  bruises heal

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Figure 12.1a The functions of cell division
Reproduction
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Figure 12.1b The functions of cell division
Growth and development
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Figure 12.1c The functions of cell division
Tissue renewal
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Key to cell division is the copying and equal
separation of chromosomes.

• Chromosomes carriers of the genetic material
  that is copied and passed from generation to
  generation
• made up of DNA and protein
• cells of every org have a specific number of
  chromosomes
• not visible in cells except during cell
  division

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Figure 12.0 Mitosis
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Figure 12.2 Eukaryotic chomosomes
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Chromosomes

• Spend most of their time as Chromatin long
  strands of DNA that are wrapped around proteins
  and appear hazy and unorganized through the
  microscope this loose arrangement is necessary
  for copying to occur.
• When get ready to divide, the chromatin coils and
  condenses into what we call Chromosomes.
• When visible, consist of two identical sister
• Chromatids that are joined in the center at
  the
• Centromere

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Figure 12.3 Chromosome duplication and
distribution during mitosis
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The Cell Cycle

• The sequence of growth and division of a cell.
• During this time, a cells grows, prepares for
  division, and divides to form two daughter cells.
• The cell cycle consists of 4 phases
• G1 phase, S phase, G2 phase, M phase

Interphase
Mitosis
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Figure 12.4 The cell cycle
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Concept Map of all events of Cell Cycle
Section 10-2
Cell Cycle
includes
is divided into
is divided into
Go to Section
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Interphase G1, S, and G2

• Interphase is very long (cells spend most of time
  here)
• G1 phase cell growth cells increase in size
  and synthesize new proteins and organelles
• S phase chromosomes are replicated and the
  synthesis of DNA molecules takes place key
  proteins associated with the chromosomes are
  synthesized during this time
• G2 phase shortest of 3 phases many of the
  organelles and molecules required for cell
  division are produced

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Interphase
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M phase MitosisPMAT

• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase -- 1st and longest phase

• chromosomes become visible (coil and condense)
• centrioles separate and take up positions on
  opposite sides of the nucleus
• chromosomes become attached to spindle fibers
• nucleolus disappears, nuclear membrane breaks down

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Chromatin condenses into chromosomes
Homologous pairs of chromosomes separate into
chromatids
2 identical daughter cells form when sister
chromatids separate
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Mitosis
Prophase
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Metaphase shortest phase

• Chromosomes line up in center of cell along
  equator on their spindles

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Figure 12.6 The mitotic spindle at metaphase
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Mitosis
Metaphase
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Anaphase

• Centromeres that join the sister chromatids
  separate
• NOW EACH CHROMATID IS A SEPARATE CHROMOSOME.
• Chromosomes continue to move until they have
  separated into two groups near the poles of the
  spindle
• Over when the chromosomes stop moving

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Mitosis
Anaphase
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Telophase final phase of mitosis

• Chromosomes begin to relax back down into
  chromatin
• Nuclear envelope re-forms around each cluster of
  chromosomes
• Spindle begins to break apart and nucleolus
  reappears in each daughter cell
• MITOSIS IS NOW COMPLETE, BUT NOT CELL DIVISION..

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Figure 12.5x Mitosis
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Mitosis
Telophase
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Cytokinesis

• Division of the cytoplasm itself
• Can take place in a number of ways
• in animal cells draw-string effect
• in plant cells cell plate forms from inside
  out, and cell wall begins to appear

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Figure 12.8 Cytokinesis in animal and plant cells
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How do cells know when to divide?

• Closeness of neighboring cells
• Presence of proteins called CYCLINS
• 2 types internal regulators
• external regulators

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Mitosis
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When cells come into contact with other cells,
they stop growing..
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Cyclins

• Regulate the timing of the cell cycle in
  eukaryotic cells
• TYPES
• Internal regulators respond to events inside
  the cell Ex. Dont begin mitosis until all
  chromos are copied
• External regulators respond to events outside
  the cell direct cells to speed up or slow down
  the cell cycle. Ex. Growth factors that
  stimulate the growth and division of cells are
  external regulators

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Uncontrolled Cell Growth

• If growth is not controlled, then crowding and
  even tissue damage may result
• Ex. Cancer disorder where bodys own cells lose
  the ability to control growth can crowd and even
  damage tissue in surrounding area forms tumor
• Benign vs. malignant tumors benign are
  localized and not spreading malignancies are
  capable of breaking off and starting up in
  another location -- metastasis

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Figure 12-17x1 Breast cancer cell
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Figure 12.17 The growth and metastasis of a
malignant breast tumor
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Figure 12-17x2 Mammogram normal (left) and
cancerous (right)