Download Chromosomes

Chapter 10
Cell Growth &
Division
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10 –1 Cell Growth
• Which has larger cells: an
adult elephant or a baby
elephant?
• Neither! They are the same
size. The adult just has more
cells.
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Division of the Cell
• Cell divides into 2 new daughter
cells.
• DNA replication occurs before division
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10–2 Cell Division
• Every cell must first copy its genetic
information before cell division begins.
– Each daughter cell then gets a complete copy
of that information.
• Eukaryotes are more complex than
Prokaryotes. In Eukaryotes:
– The first stage, division of the cell nucleus, is
called mitosis.
– The second stage, division of the cytoplasm,
is called cytokinesis.
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Chromosomes
• Genetic information is passed on from one
generation of cells to the next
• Chromosomes – made up of DNA and
proteins
• Every organism has a specific number of
chromosomes
– fruit flies = 8 chromosomes
– humans = 46 chromosomes
– carrot = 18 chromosomes
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Chromosomes (cont.)
• Chromosomes not visible except during
cell division…otherwise the DNA and
proteins are spread throughout the
nucleus.
• At beginning of cell division, chromosomes
condense and are visible.
• Before cell division, each chromosome is
duplicated.
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Parts of the Chromosome
• chromatids – sister chromatids: each
chromosome consists of 2 identical sister
chromatids. (separated during cell division)
• centromere – where each pair of
chromatids is attached near center
• Entering cell division in humans = 46
chromosomes each with sister chromatids.
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The Cell Cycle
• Recurring events in the life of the
cell.
• The series of events that cells go
through as they grow and divide
• During the cell cycle, a cell grows,
prepares for division, and divides to
form two daughter cells, each of
which then begins the cycle again.
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The Cell Cycle
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4 Phases of the Cell Cycle
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•
•
•
G1  S  G2  M
G1 = intense growth and activity
S = Chromosome replication
G2 = intense growth and activity
[Interphase = G1, S, G2 ]
M = Mitosis (nucleus division) and
cytokinesis (cytoplasm division)
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The Cell Cycle Animation
• http://www.cellsalive.com/cell_cycle.htm
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Events of the Cell Cycle
• G1 = cells do most of their growing.
• During this phase, cells increase in size and
synthesize new proteins and organelles.
• S = chromosomes are replicated
• synthesis of DNA molecules
• Key proteins associated with the chromosomes are
also synthesized
• G2 = shortest phase of interphase
• organelles and molecules required for cell division
are produced
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Mitosis
• 4 phases: [P M A T]
– Prophase
– Metaphase
– Anaphase
– Telophase
• Lasts from a few minutes to several days
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Prophase
• Longest phase of mitosis (50 to 60 percent
of the total time of Mitosis)
• Chromosomes become visible
• Centrioles separate – go to opposite ends
of the cell
• Condensed chromosomes become
attached to fibers in the spindle at a point
near the centromere of each chromatid
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Prophase (cont.)
• Nucleolus disappears
• Nuclear envelope breaks down
• Chromosomes coil more tightly
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Early prophase
Mid prophase
Late prophase
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Metaphase
• Lasts only a few minutes
• The chromosomes line up across the
center of the cell
• Microtubules (spindle fibers) connect the
centromere of each chromosome to the
two poles of the spindle
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Anaphase
• The centromeres split
• Sister chromatids separate  become
individual chromosomes
• Chromosomes continue until they have
separated into two groups near the poles
of the spindle
• Anaphase ends when the chromosomes
stop moving
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Telophase
• Chromosomes begin to uncoil into a
tangle of dense material
• A nuclear envelope re-forms around
each cluster of chromosomes
• The spindle begins to break apart
• A nucleolus becomes visible in each
daughter nucleus
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Mitosis Animation
• http://www.cellsalive.com/mitosis.htm
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Cytokinesis
• Two nuclei — each with a full set of
chromosomes — are formed, within the
cytoplasm of a single cell
• The division of the cytoplasm itself
• Occurs at the same time as telophase
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Animal Cells vs. Plant Cells
• animal cells = cell membrane is drawn inward
until the cytoplasm is pinched into two nearly
equal parts
• plants = the cell plate forms midway between
the divided nuclei
– The cell plate gradually develops into a separating
membrane.
– A cell wall then begins to appear in the cell plate.
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10-3 Regulating the Cell Cycle
• Controls on Cell Division
– When cells come into contact with each other,
cells respond by stopping growth (petri dish)
– when put with space between cells, cells
begin growing once again.
– controls on cell growth can be turned on and
off
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Contact Inhibition
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In the body
Cut the skin or break a bone
• Cells at the edges of the injury are
stimulated to divide rapidly.
• Produce new cells
• When the healing process nears
completion, the rate of cell division slows
down
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Uncontrolled Cell Growth
• Cancer cells do not respond to the
signals that regulate the growth of most
cells
• Divide uncontrollably
• Form masses of cells called tumors
• May break loose from tumors and spread
throughout the body
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Causes of cancer
• smoking tobacco
• radiation exposure
• even viral infection
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Why does cancer occur?
Many cancers have a defect in a gene called
p53
• p53 normally halts the cell cycle until all
chromosomes have been properly
replicated
• Damaged or defective p53 genes cause
the cells to lose the information needed to
respond to signals that would normally
control their growth
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