Cell Growth and Division

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Cell Growth and Division

• Chapter 10 page 240-259

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10-1 Cell Growth

• pp. 241-243

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Limits Cell Growth

• DNA overload
• Exchanging materials
• Surface area-to-volume ratio
• Examples of cells sizes
• Red blood cells measure only 8 micrometers in
  diameter
• Some animal cells reach up to 1 meter (nerve
  cells)

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DNA limits cell size

• Cells need proteins to survive
• There are limits to how quickly the blueprints
  for proteins can be copied in the nucleus and
  made into the proteins in the cytoplasm
• i.e. the speed of protein synthesis
• Examples
• Pelomyxa uses large amounts of DNA in many
  nuclei to ensure that cell activity is carried
  out quickly and efficiently

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Diffusion limits cell size

• Diffusion
• fast and efficient over short distances
• loses speed and efficiency as it moves over a
  longer distance.

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Surface area-to-volume ratio

• As a cell increases, its volume increases much
  faster than its surface area
• If the cells size doubles, then the cell would
  require 8x more nutrients and would have 8x more
  waste to excrete
• The cell would not have enough surface area
  through which O2, nutrients, and waste could
  diffuse
• Results in cell death

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Surface area-to-volume ratio
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Division of the Cell

• Cell division is when a cell divides into two new
  daughter cells.
• Before this occurs, the cell replicates (makes
  copies) of itself.
• Results
• Each daughter cell has its own genetic info

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10-2 Cell Division

• pp. 244-252

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Cell division

• Process by which new cells are produced from one
  cell
• Results in 2 cells that are identical to the
  parent cell
• Occurs in two main stages
• Mitosis division of the cell nucleus
• Cytokinesis division of the cytoplasm

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Chromosomes

• chroma colored soma body
• Scientist noticed chromosomes forming before cell
  division
• Chromosomes
• structures which contain DNA and become darkly
  colored when stained
• Carries the genetic material necessary for living
  organisms

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Chromosomes (continued)

• Chromosomes will exist as chromatin for much of
  the cells life
• It is only chromosomes during cell division
• Chromatin
• Long strands of DNA wrapped around proteins
• This unorganized arrangement is necessary for
  copying the protein blueprints (mRNA)

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Chromosomes (continued)

• Each chromosome consists of two identical sister
  chromatids which separate from each other when
  the cell divides.
• One chromatid goes to each new cell.
• The chromatids are attached to each other by an
  area known as the centromere.

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Cell Cycle

• It is a series of events that a cell undergoes as
  it grows and divides
• Three things occur during the cell cycle
• Growth
• Preparation to divide
• Divides to form two daughter cells

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Events of the Cell Cycle

• Interphase
• G1
• S
• G2

• Mitosis (PMAT)
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis

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Interphase

• Majority of the cells life
• Interval between mitotic divisions
• Cell is growing and preparing for mitosis
• Composed of 3 phases
• Absence of visible chromosomes
• chromatin

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Phases of Interphase

• G1
• Cell growth (in size)
• Matures (produces new proteins organelles)
• S
• DNA is synthesized
• Replicated
• Sister chromatids form
• G2
• Prepare for mitosis
• Centriole pair replicate
• mother cell

• G0
• Cells are not dividing
• Cell withdraws from cell cycle

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Mitosis

• Pg. 246-248

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Characteristics of Mitosis

• Process of growth
• Asexual reproduction
• Results in 2 identical cells
• Unicellular organisms remain single-celled
• Multicellular organisms results in groups of
  cells working together (pg. 193)
• Tissue ? Organ ? Organ system

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Steps of Mitosis

• Karyokinesis
• Nuclear division
• Genetic material is separated into 2 daughter
  cells
• Occurs during anaphase
• Cytokinesis
• Division of the cytoplasm
• Results in 2 cells being formed
• Different in plant and animal cells

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Phases of Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase
• PMAT

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Prophase

• First and longest phase of mitosis
• Chromatin condense into chromosomes
• Nuclear membrane and nucleolus disappear
• Animal cells - centrioles migrate to the poles
• Two tiny structures located in the cytoplasm near
  the nuclear envelop
• Spindles form
• Fanlike microtubule structures that help separate
  the chromosomes
• In plant cells they form without the centrioles

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Metaphase

• Short, second phase
• Chromosomes become attached to the spindle fibers
  via centromere
• Chromosomes line up at the metaphase plate
  (equatorial plate)

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Anaphase

• Third phase
• Karyokinesis
• separation of sister chromatids
• centromere split apart
• Sister chromatids are pulled toward the poles

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Telophase

• Final phase of mitosis
• Begins when sister chromatids reach the poles
• Reversal of prophase
• Nuclear membrane and nucleolus reappear
• Chromosomes unwrap into a tangle of dense
  material (chromatin)
• A new double membrane begins to form between the
  2 new nuclei

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Cytokinesis

• pp. 248-249

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Cytokinesis in Animal Cells

• The plasma membrane pinches in along the equator
• Cleavage furrow
• 2 new cells are separated

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Cytokinesis in Plant Cell

• Plasma membrane does not pinch off
• Cell plate is laid down across the equator
• Cell membrane is formed around each cell
• A new cell wall forms on each side of the cell
  plate

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10-3 Regulating the Cell Cycle

• pp. 250-252

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Controls on Cell Division Cell Cycle Regulators

• Cells will divide as long as there is space
  available.
• Cyclins regulate the timing of the cell cycle in
  eukaryotic cells.
• Internal Regulators
• Proteins responding to events inside the cell
• i.e., prevent entering mitosis prematurely or
  regulating when each phase should begin

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Controls on Cell Division Cell Cycle
Regulators (continued)

• External Regulators
• Proteins that respond to event outside the cell
• i.e., speed up or slow down the cell cycle
  (growth regulators)

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Checkpoints control the cell cycle

• G1 checkpoint
• Checks cell size and suitable environment
• G2 checkpoint
• Checks replicated DNA, if the cell is large
  enough, suitable environment
• Metaphase checkpoint
• Checks if chromosomes are aligned on spindles

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Cancer Uncontrolled Cell Growth
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Characteristics of Cancer

• Occurs when cells do not respond to the signals
  that regulate growth
• Form masses of tissue called tumors that deprive
  normal cells of nutrients
• 2nd leading cause of death in the USA

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Causes of Cancer

• Environmental factors
• Geographic location, cigarette smoke, air and
  water pollution, and exposure of UV light
• Viral infections
• Damaged genes
• p53

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Cancer prevention

• Diets low in fat and high in fiber
• Diets high in fat are linked to colon, breast,
  and prostate cancers
• Vitamins and minerals
• Carotenoids
• Vitamin A, C, E
• Calcium
• Daily exercise
• Not using tobacco products

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Cell Cycle Web Links

• http//www.cellsalive.com/cell_cycle.htm
• http//www.cellsalive.com/mitosis.htm