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Cell Growth and Division
Ch. 10
Cell Size and Limitation
• Cells come in a variety • What is diffusion?
of sizes.
– Diffusion limits cell
size
– DNA content limits
size
Diffusion and DNA limit cell size
because…
• Cells rely on diffusion
to carry on proper
functions
– Cells require a constant
supply of glucose and
oxygen
– Cells must constantly
get rid of waste.
• DNA is found in all
cells.
– The larger the cell, the
greater number of
enzymes
– DNA makes enzymes
needed for the cell
Is bigger better?
• Surface Area to
Volume Ratio
– As the cell size
increases, its volume
increases 2x
faster….why is this a
problem?
Other ways to solve
the problem
• If cell size doubled, it
would be an 8 fold
increase in volume, but
the surface area would
only increase 4 fold.
Therefore, there is not
enough membrane for
nutrients to flow through
to keep the cell alive.
How do cells overcome this
problem?
• What do you think?
– How will you get more
membrane to
compensate for the
volume?
• They divide into 2
cells allowing for
twice as much
membrane to be
formed.
1.7a Cell growth and division are caused by complex
interactions between the different kinds of molecules in
the cell.
3 purposes of cell division
1. Growth
• 1.8a All growth and
development within a
2. Repair
cell
is
a
consequence
3. Reproduction
of an increase in cell
a. Asexual- offspring
number, size and/or
produced only by one
products.
parent. (bacteria) Not much
variation.
b. Sexual- produces offspring
that have a combination of
genetic material from two
parent organisms. Lots of
variation.
Rate of Cell Division
• The Pituitary gland
secretes a growth
hormone that tells
cells when to divide
and how much. If you
lack this hormone,
dwarfism may occur.
1.7b Molecules from different parts of the cells, such
as hormones, can affect cell behavior.
Structure of eukaryotic
chromosomes
• Before cell division, each
chromosome is replicated.
• Each chromosome consists
of 2 identical sister
chromatids.
• Each sister chromatid will
separate from each other
during cell division and go
into its new cell.
• When chromatin coils
it becomes
______________?
1.1a All of the cells in your body come from a single cell
that differentiates into many different cells, but they all
essentially have the same genetic instructions.
• 1.11 All organisms
begin their life cycles
as a single cell, and in
multicellular
organisms, new
generations of
embryonic cells form
by cell division.
1.8b Cells differentiate from each other because of
gene expression and/or environmental influences.
• Certain genes can be
turned off or on at
certain time.
(Expresses or not
expressed).
• The environment can
influence what cells
are expressed or not.
This also causes cells
to differentiate.
The Cell Cycle
• The cell cycle is the
repeated sequence of
cell growth
(interphase) followed
by cell division
(mitosis)
• 5 phases
–
–
–
–
–
Interphase
Prophase
Metaphase
Anaphase
Telophase
Mitosis
Mitosis- process of nuclear division followed by cytoplasmic division.
Interphase…a busy time (90% of
cell cycle)
• Cell activities during
interphase:
–
–
–
–
–
–
–
–
–
Make ATP
Repairing themselves
Excreting wastes
Making proteins
Producing new organelles
Duplicating DNA
Chromatin duplicates
Metabolism
Cell growth in size
• 3 phases:
– G1: normal growth
phase (9 hours)
– S: DNA is replicating
(10 hours)
– G2: final growth in
preparation for mitosis
(2 hours)
Structure of the Chromosome
• Each chromosome has
two identical partssister chromatids that
are held together by a
centromere.
Other structures used..
• Centrioles are a pair of
cylindrical structures made of
microtubules that are only found
in animal cells and found just
outside the nucleus.
• Spindles are cagelike structures
that are made of microtubules
and used to separate sister
chromatids.
• Spindle fibers are the individual
microtubules of the spindle.
Prophase- the first phase
• Chromatin coils and
becomes chromosomes.
• The nucleus disappears.
• Centrioles migrate to
opposite poles of the cell.
• The spindle forms and
attaches to the centrioles
and centromere.
Metaphase- the
• Chromosomes line up
along the equator
• Spindle fibers attach
to the centromeres.
nd
2
phase
Anaphase- the
• Sister chromatids
separate and
centromeres split
apart.
rd
3
phase
Telophase- the
• The “reverse” of
prophase
– Chromosomes uncoil
to make chromatin
– Spindle fibers
disappear
– Nucleus forms
– Plasma membrane
begins to from between
2 nuclei.
th
4
phase
The final step
• Cytokinesis- the division of
the cytoplasm that results
in two new daughter cells.
• In plants, a cell plate forms
across the equator, so the
membrane doesn’t have to
pinch in.
• ** Centrioles are not found
in plant cells during cell
division.
Mitosis in motion
The result
• Each new daughter cell will have complete set of genetic
material.
Cell Cycle Regulators
• Cyclins are proteins that
regulate the timing of the cell
cycle in eukaryotic cells.
• Internal Regulators- proteins
that respond to events inside
the cell. Allow cell cycle to
proceed only when certain
processes have happened.
• External Regulators- direct
cells to speed up or slow
down cell cycle.
External or Internal?
– Make sure cell doesn’t
enter mitosis until all its
chromosomes have been
replicated.
– Growth factors.
– Prevents cell from entering
anaphase until all of its
chromosomes are attached
to mitotic spindle.
Enzymes control the cell
• Some control progression
from one phase to another.
• Come inhibit progression.
• If too much or not enough
is produced it can lead to
cell death or cancer.
• Genes control enzyme
production.
• Contact inhibition is
another way the cell
cycle is controlled.
Cells normally stop
dividing when they
come into contact with
each other.
1.7a Cell growth and division are caused by
complex interactions between the different
kinds of molecules in the cell.
Cancer..A Mistake in the Cycle
• Cancer is thought to be
due to changes in genes
that make enzymes
involved in the cell cycle.
• Cells divide when they
shouldn’t.
• Cancer cells do not
respond to the signals that
regulate the growth of
most cells.
• Cancer cells can break
away from a tumor (large
mass) and travel through
the blood to other areas in
the body.
• Gene p53 normally stops
the cell cycle until all
chromosomes have been
replicated, but if there is a
defect, growth is not
controlled.
Other causes of cancer
•
•
•
•
Cigarette smoke
Air and water pollution
UV radiation
Certain viruses
– Cervical cancer -HPV
– Mesothemioma
– Liver cancer- Hep B
• Some people may be born
with genetic mistakes
which may cause cancer.
– Gene p53.
• Cancer is the 2nd
leading cause of death
in the U.S. Heart
disease is #1.
Stem Cells
• Stem cells are unspecialized
• Neurons are noncells that have the potential to
replaceable.
differentiate to become
specialized in structure and
• Embryonic stem cell
function into a wide variety of
research is very
cell types.
controversial because the
• In early embryonic development,
cells are taken from a
stem cells produce every type of
human embryo.
tissue in the body.
• Transplants fail- different
• Stem cells in bone marrow can
genetic info.
make more than a dozen types of
blood cells.
3 kinds of stem cells
1. Totiopotent- the egg and the cells that result
from early cell division. Human fertilized egg
has the potential to form a whole organism.
2. Pluripotent- forms five days after fertlization
(blastocyst- outer layer of cells and inner cell
mass). Inner cells form tissue of human.
3. Mulitpotent- pluripotent cells specialize further
to give rise to specialized cells. Present in adults.
Which type of cells do you think are used for
medical therapies? Why?
Pluripotent
Cell Cycle Review
• Click on the following link, then click on
your book and go to Ch. 10 and take the
Self-Test and do the Active Art.
• Ch. 10 Review