Biology

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Biology

• Ch. 10
• Cell Growth and Division
• Core Content SC-HS-3.4.3

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101 Cell Growth

• A. Limits to Cell Growth
• 1. DNA Overload
• 2. Exchanging Materials
• 3. Ratio of Surface Area to Volume
• 4. Cell Division

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Limits to Cell Growth

• The larger a cell becomes, the more demands the
  cell places on its DNA.
• The cell has DNA overload, and the needs of the
  growing cell can no longer be met.
• The more trouble a cell has moving enough
  nutrients and wastes across the cell membrane.

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Surface area to Volume Ratio

• As a cell grows, the volume of the cell increases
  faster than the surface area.
• The resulting decrease in the cells ratio of
  surface area to volume makes it difficult for the
  cell to move needed materials in and waste
  products out.

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Ratio of Surface Area to Volume in Cells
Cell Size
Cell Size
Surface Area (length x width x 6)
Surface Area (l x w x 6)
Volume (l x w x h)
Surface area to Volume ratio
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102 Cell Division

• A. Chromosomes
• B. The Cell Cycle
• C. Events of the Cell Cycle
• D. Mitosis
• 1. Prophase
• 2. Metaphase
• 3. Anaphase
• 4. Telophase
• E. Cytokinesis

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Cell Division

• Before it becomes too large, a growing cell must
  divide into two daughter cells. This is cell
  division.
• Before cell division occurs, the cell copies its
  DNA. This ensures that each daughter cell gets a
  complete set of genetic information.
• Division increases the cells surface area to
  volume ratio.

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Chromosomes

• Chromosomes are made of DNA, which carries the
  cells coded genetic information, and proteins.
• Cells of each organisms have a specific number of
  chromosomes. Ex) humans have 46
• Chromosomes are not visible except during cell
  division.
• Each chromosome consists of two identical
  sister chromatids that are attached at the
  centromere.

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The Cell Cycle

• During the cell cycle, a cell grows, prepares
  for division, and divides to form two new
  daughter cells.
• Interphase is the period between divisions, and
  includes G1, S, and G2 phases.
• The M phase follows interphase, and includes
  mitosis and cytokinesis.

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Concept Map
Section 10-2
Cell Cycle
includes
is divided into
is divided into
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Interphase

• Interphase takes much longer than actual cell
  division.
• G1 Cells do most of their growing. Cells
  increase in size and synthesize new proteins and
  organelles.
• S DNA is copied
• G2 Cell prepares for mitosis, makes organelles
  and structures needed for cell division

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Figure 104 The Cell Cycle
Section 10-2
G1 phase
M phase
S phase
G2 phase
Go to Section
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Mitosis

• Following the events of Interphase, the cell will
  begin to divide. This is mitosis.
• Biologists divide mitosis into four phases
  prophase, metaphase, anaphase, and telophase

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Prophase

• The first and longest phase of mitosis is
  prophase.
• During prophase, the chromatin condenses to form
  chromosomes.
• The centrioles separate, and a spindle begins to
  form.
• The nuclear membrane breaks down.

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Metaphase

• The stage following prophase is metaphase.
• During metaphase, the chromosomes line up across
  the center of the cell.
• Each chromosome is connected to a spindle fiber
  at its centromere.

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Anaphase

• Following metaphase is anaphase.
• During anaphase, the sister chromatids separate
  into individual chromosomes and are moved apart.
• The chromosomes form groups near the poles of the
  spindle.
• Anaphase ends when the chromosomes stop moving.

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Telophase

• The fourth and final stage of mitosis is
  telophase.
• The chromosomes gather at opposite ends of the
  cell, and lose their distinct shapes.
• Two nuclear membranes begin to form.

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Cytokinesis

• Cell division is not complete until cytokinesis
  occurs. Cytokinesis is division of the
  cytoplasm.
• In animal cells, the cell membrane is drawn
  inward until the cytoplasm is pinched into two
  equal parts.
• In plants, a cell plate forms midway between the
  divided nuclei. The cell plate gradually
  develops into a separating membrane.

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Cleavage furrow in animal cells
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Cell plate forming in plant cell
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93 Regulating the Cell Cycle

• A. Controls on Cell Division
• B. Cell Cycle Regulators
• 1. Internal Regulators
• 2. External Regulators
• C. Uncontrolled Cell Growth

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Cell Cycle Regulators

• Cyclins regulate the timing of the cell cycle in
  eukaryotic cells.
• Proteins that respond to events inside the cell
  are called internal regulators.
• Proteins that respond to events outside the cell
  are called external regulators.
• Most cells grow until they come in contact with
  other cells, then they stop (contact inhibition).

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Control of Cell Division
Go to Section
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Section 10-3
Figure 108 Effect of Cyclins
A sample is injected into a second cell in G2 of
interphase.
A sample of cytoplasm is removed from a cell in
mitosis.
As a result, the second cell enters mitosis.
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Uncontrolled cell growth

• Cancer cells do not respond to the signals that
  regulate the growth of most cells.
• A defect in a gene called p53 has been found in
  many types of cancer cells.
• They continue to grow out of control, and can
  form masses of cells called tumors.
• Tumors can damage surrounding tissues.

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Benign vs. Malignant tumors

• If the abnormal cells remain at the original
  site, the tumor is BENIGN and can usually be
  surgically removed.
• If the tumor invades other organs and impairs
  their function, the tumor is MALIGNANT.
• The spreading of cancer cells is METASTASIS.

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BREAST CANCER
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BREAST CANCER CELL
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NORMAL MAMMOGRAM
CANCEROUS MASS
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• Apoptosis
• Programmed cell death.
• Usually shrink and shrivel in a controlled
  process.
• Example development of hands and feet. Your
  hands and feet have webbing between them in
  utero. But when a baby is born this webbing is
  gone because of apoptosis.
• Example leaves falling off trees and plants in
  autumn.

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• Stem Cells
• Unspecialized cells that can develop into
  specialized cells when under the right
  conditions.
• Two types Embryonic and adult stem cells.
• Embryonicafter fertilization the resulting mass
  of cells divides rapidly until there are about
  100-150 cells. These are cells that have not
  become specialized yet and can be used to repair
  damaged cells in others but is highly
  controversial.

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• Adult stem cellsfound in various tissues in the
  body and might be used to maintain and repair the
  SAME kind of tissue in which they are found.