Download Chapter 10 Roche Bio

Chapter 10
Cell Growth and Division
Cell division and mitosis
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10-1
 Why
Cell Size
do organisms have millions of
cells instead of just a few?
 Why are there limits to how big a
cell can become?
Cell Size

Cells use food, oxygen and water and
produce wastes from these processes
◦ The rate depends on the cell’s volume – the
amount inside the cell membrane

Cells move food, oxygen, water and wastes
in and out through the cell membrane.
◦ The rate depends on the cell’s surface area – the
measurement of the outside surface of the cell –
the cell membrane
Limits to Cell Growth

The larger a cell becomes,
◦ The more demands it places on its DNA
◦ It becomes more difficult to move enough
nutrients and wastes across the cell
membrane
◦ If there is more space between the cell’s
membrane and the center of the cell, it takes
longer to move materials in and out
Ratio of Surface Area to Volume
As the length of the cell increases, the
volume increases faster than the surface
area!
 The RATIO of surface area to volume
decreases!

*** This number needs to be large! ****
Now it is too difficult for cell to move
needed materials in & waste products out
quickly enough.
 At this point the growing cell divides into
two smaller “daughter” cells.

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10-2
 In
Cell Division
eukaryotic cells, cell division occurs
in two major stages:
1. mitosis: division of the cell nucleus
2. cytokinesis: division of the cell
cytoplasm
 Chromosomes: carry genetic
information
◦ Before cell division, each
chromosome is duplicated, or copied.
Chromosomes
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9
Chromosomes
◦ Each chromosome
consists of two
identical “sister”
chromatids.
◦ Each pair of chromatids
is attached at an area
called the
centromere.
◦ When the cell divides,
the chromatids
separate.
◦ Each new cell gets one
chromatid.
Sister chromatids
Centromere
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The Cell Cycle
A
series of events that cells go through
as they grow and divide
 Interphase is a period of growth that
occurs between cell divisions
The Cell Cycle has four phases
1.
◦
◦
2.
◦
◦
3.
◦
4.
◦
◦
G1 = First Gap Phase = growth phase
Cell increases in size
Cell synthesizes new proteins and organelles
S Phase = synthesis phase
Chromosomes replication
DNA synthesis
G2 = Second Gap Phase
Organelles and molecules needed for cell
division (mitosis) are produced
M Phase = Mitosis
Mitosis has four phases: prohase, metaphase,
anaphase and telophase.
Followed by cytokenisis.
Events of
the
Cell Cycle
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Phases of Cell Division





Prophase
◦ Centrioles and spindle forms
◦ Nuclear envelope breaks down
◦ Chromosomes become visible
Metaphase
◦ Chromosomes line up in the middle of the
cell
◦ Spindle connects to centromeres
Anaphase
◦ Chromosome pairs are separated
Telophase
◦ Chromosomes gather at either end
◦ Nuclear envelope re-forms
Cytokinesis
◦ Cytoplasm pinches
◦ Two daughter cells are made
Mitosis =
Division
of
Nucleus
10-2 Cell Division
Mitosis
Prophase
Spindle
forming
Prophase is the first
and longest phase of
mitosis.
The centrioles
separate and take up
positions on opposite
sides of the nucleus.
The spindle is a fanlike
microtubule structure
that helps separate the
chromosomes.
Centromere
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Chromosomes
(paired
chromatids)
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10-2 Cell Division
Mitosis
Spindle
forming
Chromatin condenses
into chromosomes.
The centrioles separate
and a spindle begins to
form.
The nuclear envelope
breaks down.
Centromere
Chromosomes
(paired
chromatids)
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10-2 Cell Division
Mitosis
Centriole
Metaphase
The second phase of
mitosis is metaphase.
The chromosomes line
up across the center of
the cell.
Microtubules connect
the centromere of each
chromosome to the
poles of the spindle.
Spindle
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10-2 Cell Division
Mitosis
Anaphase
Individual
chromosomes
Anaphase is the third
phase of mitosis.
The sister chromatids
separate into individual
chromosomes.
The chromosomes
continue to move until
they have separated into
two groups.
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10-2 Cell Division
Mitosis
Telophase
Telophase is the
fourth and final phase
of mitosis.
Chromosomes gather
at opposite ends of the
cell and lose their
distinct shape.
A new nuclear
envelope forms
around each cluster of
chromosomes.
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Slide
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10-2 Cell Division
Cytokinesis
Cytokinesis
During cytokinesis, the
cytoplasm pinches in
half.
Each daughter cell has
an identical set of
duplicate
chromosomes.
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10-2 Cell Division
Cytokinesis
In plants, a cell plate forms midway between the divided
nuclei, developing into a separating membrane. A cell wall
then appears in the cell plate.
Cell plate
Cell wall
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10-3
Controls on Cell Division
Experiments have shown that normal cells
will reproduce until they come into
contact with other cells.
 They respond by not growing.
 This demonstrates that controls on cell
growth and division can be turned on and
off.

10-3 Regulating the Cell Cycle
Controls on Cell Division
Contact Inhibition
Slide
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Cell Cycle Regulators - CYCLINS
Cyclins are proteins that regulate the timing
of the cell cycle in eukaryotic cells.
 The amount of cyclin in cells rises and falls in
time with the cell cycle

10-3 Regulating the Cell Cycle
Cell Cycle Regulators
Cyclins were discovered during a similar
experiment to this one.
A sample of cytoplasm
is removed from a cell
in mitosis.
The sample is injected
into a second cell in
G2 of interphase.
As a result, the
second
cell enters mitosis.
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10-3 Regulating the Cell Cycle
Cell Cycle Regulators
Cyclins were discovered during a similar
experiment to this one.
A sample of cytoplasm
is removed from a cell
in mitosis.
The sample is injected
into a second cell in
G2 of interphase.
As a result, the
second
cell enters mitosis.
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Internal and External Cell Regulators

Internal:
◦ Proteins that respond to events inside the cell
◦ Allow cell cycle to proceed only when certain
processes have occurred inside the cell

External:
◦ Proteins that respond to events outside the cell
◦ Direct cells to speed up or slow down the cell
cycle
Uncontrolled Cell Growth - Cancer
A disorder in which some of the body’s
cells lose the ability to control growth
 Cancer cells don’t respond to the signals
that regulate growth
 Cancer cells divide uncontrollably forming
masses of cells called tumors;

◦ Tumors can damage surrounding tissues
◦ Cancer cells can break loose from tumors and
spread throughout the body