Transcript Chapter 8 Cellular Transport and the Cell Cycle

Chapter 9 Cellular
Reproduction
9.1 Cellular Growth
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Cells Come in Different Sizes
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Red Blood Cell 8
um in diameter
Nerve Cell 1 m in
length with very
small diameter
Yolk of ostrich egg
8 cm
Most cells are 2200 um
1000 um = 1 mm
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Limits to Cell Size
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2.
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Diffusion
DNA
Surface to volume ratio
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Diffusion Limits Cell Size
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Within the cell nutrients must diffuse to all
parts
Diffusion is based on random movement
of particles
Diffusion is too slow for a large cell
When cells reach maximum size they die
or divide
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DNA Limits Cell Size
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DNA contains all the instructions for
synthesizing proteins (including enzymes)
Large cells would need more proteins
More copies of the DNA instructions would
be needed for a large cell
Most cells contain only one set of DNA
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Surface Area to Volume Ratio
Limits Cell Size
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As the size of a cell increases the volume
increases faster than the surface area
If the cell size is doubled then need eight
times more nutrients but plasma
membrane is only four times larger
Cells divide before they become too large
to function properly
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Volume Increases Faster than
Surface Area
What are the surface area to volume ratios?
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The Cell Cycle
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Sequence of growth and division of a cell
Two main periods
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Growth also called interphase
Division also called mitosis and cytokinesis
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Cell Cycle
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Interphase
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NOT part of mitosis, rather the time
between one mitosis and the next
Stages of interphase
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G1 phase: rapid growth and metabolic activity
S phase: synthesis of DNA (additional copy is
made)
G2 phase: centrioles and other organelles
replicate; cell prepares for division
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Chromosomes and Chromatin
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Both are DNA
Chromosomes are the condensed form of
DNA that is visible as individual strands.
Chromatin is the “relaxed” very thin form
of DNA that is not visible as individual
strands.
During interphase DNA is in the chromatin
form.
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Chromosomes and Chromatin
Chromatin DNA form
Chromosome DNA form
Chromatin DNA form
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Cell Reproduction
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Process of producing
new cells from
preexisting cells
Three Types
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Fission: bacteria
Meiosis: sex cells
Mitosis: body cells
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Needed for growth
Needed for repair
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Bacteria Reproduce by Fission
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Prokaryotes do not
have a nucleus
They divide the cell
contents then divide
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Chapter 9 Cellular
Reproduction
9.2 Mitosis and Cytokinesis
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Eukaryote Cell Reproduction is
Mitosis and Cytokinesis
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Mitosis is division of the
nucleus producing two
genetically identical
daughter cells from one
parent cells
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Needed for growth
Needed for repair
Cytokinesis is division of
the cell contents
Usually they happen
simultaneously
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Phases of Mitosis
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Prophase
Metaphase
Anaphase
Telophase
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Chromosome Structure
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Chromosome is two sister chromatids connected by a
centromere
Chromosomes are made of DNA and contain genes
(hereditary units)
Chromosomes are the condensed form of chromatin
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Prophase
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Chromatin coils into
visible chromosomes
Nuclear membrane
disintegrates
Nucleus disappears
Centrioles migrate to
opposite ends of cell
Spindle fibers form
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Prophase
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Metaphase
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Much shorter amount
of time than prophase
Spindle fibers attach
to centromere
Chromatids line up at
the cell’s equator
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Metaphase
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Anaphase
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Centromeres split
Spindle fibers shorten
to pull chromatids to
each end of cell
Sister chromatids
separate
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Anaphase
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Telophase
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Starts when
chromatids get to
opposite poles
Chromosome uncoil
and become
chromatin
Spindles breakdown
Nuclear membrane
reforms
Nucleus becomes
visible
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Telophase
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Cytokinesis
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Division of the
cytoplasm
Plants form a cell
plate, the beginning
of a cell wall
Animals have
cleavage furrow
where the plasma
membrane pinches in
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Animal and Plant Cytokinesis
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Results of Mitosis
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Mitosis allows for
genetic continuity in
each generation of
daughter cells
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Same chromosomes
Same genes
Same exact DNA
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Levels of Organization
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In unicellular organisms one organism undergoes mitosis to make
two organisms
In multicellular organisms one cell undergoes mitosis to make two
cells that form tissues
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Tissues of different types functioning together form organs
Organs functioning together form systems
Systems functioning together form organisms
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Chapter 9 Cellular
Reproduction
9.3 Cell Cycle Regulation
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Length of Cell Cycle
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Each cell type has a specific growth and
reproduction time table
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Frog embryo cell cycle of less than one hour
Cells lining your intestine 24-48 hours
Mature nerve cells do not divide
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Normal Control of the Cell Cycle
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Much that science does not fully
understand
Enzymes control the cell cycle
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Many enzymes needed
Most enzymes are used at just one point in
the cycle
Loss of a functional enzyme can cause the cell
cycle to be “out of control”
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Normal Control of the Cell Cycle
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Signaling molecules made
of a cyclin bound to a
CDK kick off the cell cycle
and drive it through
mitosis.
Checkpoints monitor the
cell cycle for errors and
can stop the cycle if an
error occurs
CDK are enzymes, cyclins are proteins
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Genes and Proteins
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Genes located on DNA are responsible for
giving direction about what proteins
(enzymes) to produce
A defective gene would produce a faculty
enzyme that would not function correctly
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Key Time for Control of the Cell
Cycle
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Key control of the cell
cycle is just prior to S
phase during
interphase
If new DNA is
synthesized then the
cell will continue on
with mitosis
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Cancer
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A cell “out of control” of the cell cycle
Mistake in the Cell Cycle
Too fast rate of mitosis
Result of changes in one or more genes
that produce enzymes that are involved in
controlling the cell cycle
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Cancer Cells
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Cancer Cells
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Cancer cells form tumors
Tumors are masses of
cells that interfere with
normal functioning
Metastasis: cancer cells
break off the tumor and
travel to other locations
to form tumors
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Causes of Cancer
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Both genetic and environmental
When people move from one country to
another their rate of cancer is that of the
country they are now living
Example: Rate of breast cancer is high in
US and low in Japan; when people move
from Japan to US their rate of breast
cancer increases
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Environmental Causes of Cancer
Smoking
UV Light
Diet
Air Pollution
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Environmental Causes of Cancer
Water Pollution
Viruses
Cervical Cancer
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Cancer Prevention
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Clear link between healthy lifestyles and
incidence of cancer
Low fat, high fiber diet reduces risk
Daily exercise reduces risk
No tobacco in any form reduces risk
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Apoptosis
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Programmed cell death
All animal cells have a “death program”
Fetal human tail cells have undergone
apoptosis; programmed cell death at the
appropriate time
Plant leaves undergo apoptosis in autumn
when the leaves are falling
Apoptosis can help protect organisms from
developing cancerous growths.
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Stem Cells
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Stem cells are
unspecialized cells
that can develop into
specialized cells under
the right conditions
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Embryonic Stem Cells
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After a sperm fertilizes an egg the cell
divides until there is 100-150 cells
Each of these cells can develop into a
wide variety of specialized cells
Much controversy exists due to the
ethical concerns about the source of these
embryonic stem cells
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Adult Stem Cells
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Present in adults (and newborns) to
produce the same type of cell
Not pluripotent (can’t become any cell
type)
In 2000 adult stem cells ere used to
restore lost brain tissue in mice
Less controversy exists to the use of adult
stem cells
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