Cell Cycle
Limits to Cell Size
The Cell Cycle
Regulating the Cell Cycle
Limits to cell size
Why are cells so small? What advantage is
there to keep lots of small cells rather
than have one large cell?
• Specialization
• Protection and resistance to damage
• Efficiency (surface area:volume ratio)
Ratio of Surface Area to Volume in Cells
Cell Size
Surface Area (length
x width x 6)
Volume
(length x width x height)
Ratio of Surface Area
to Volume
• How far will food particles be able to diffuse into each cell?
• What factors effect transfer of material into/out of the cell?
• How is this used in the human body?
Johnson Exploration: Cell Size
• Cell Maintenance
– The work of cells is done by proteins. As a cell
gets larger, more proteins are required to maintain
its function.
– If the cell gets too large, DNA instructions cannot
be copied quickly enough to make the proteins that
the cell needs to support itself.
– Cell size is also limited by the cell’s DNA.
• Exchanging Materials (surface area:volume ratio)
– Oxygen, food, water and wastes all pass through
the cell membrane.
– How fast these can enter and exit depend on the
external surface area.
– How fast the cell uses food and oxygen depends
on the internal volume.
Summary
• The larger the cell becomes, the more
demands the cell places on its DNA
(DNA overload) and the more trouble the
cell has moving enough nutrients and
wastes across the cell membrane
(surface area:volume ratio).
• Solution: Small cells
Cell Cycle
Problem
solving: How
important is
the fist cell
division.
Reproduction
Importance link
Asexual- 1 parent
Sexual- 2 parents
Exploring Life CD
• Each time a cell reproduces, it divides
into two new cells. When each of the
new cells divide, the result is four new
cells. If this continues, how many cells
will be present after the cells
reproduce 6 times?
Binary Fission
bacteria
• Bacteria, cyanobacteria, and most
single celled organisms reproduce by
binary fission.
fission
DNA
cell membrane
M
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• Duplication of a eukaryotic somatic cell.
• Somatic Cell- body cell ex. Skin, liver etc.
Does not include: sperm or egg.
• All Somatic cells have the same number of
chromosomes.
Liver Cell
Liver Cell
2n=46
2n=46
2n=46
Results:
two
identical
daughter
cells
Liver Cell
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Interphase
Normal cell activities
Mitosis
Division of chromosomes
Cytokinesis
Division of cytoplasm
Cell cycle animation
G1 phase
Interphase
S phase
G2 phase
Prophase
C
Y
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E
G1 phase
Metaphase
Mitosis
Anaphase
S phase
Telophase
G2 phase
Cytokinesis
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N • Comprises about 90% of the cell life
cycle.
T
• What takes place at this time?
E
1. Cellular growth
R
2. protein synthesis
3. metabolic activities
P
4. DNA replication (synthesis)
H
Normal
Cell
activities
A
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E
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P
H
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1. G1 (gap) phase:
– Growth, protein synthesis and metabolic
activities. (normal activities)
G phase
– most cell exist in this phase.
phase
1
2. S (synthesis) phase:
– DNA replication
S phase
G2 phase
3. G2 (gap) phase:
– Cellular growth and preparation for
Mitosis.
Mitosis
Problem Solving- how does the cell cycle vary?
Interphase
• Nucleus and nucleolus visible.
chromatin
Nuclear
Envelope
cell
membrane
nucleolus
Question:
• What is a chromosome vs. chromatin?
• Chromosome is made up of a DNA - histone
protein complex. Chromosomes have their own
centromere.
• Chromatin is a long, thin DNA fiber before it is
coiled into a chromosome.
Nucleosome
Chromosome
Centromere
DNA
double
helix
Coils
Supercoils
Histones
What is a replicated chromosome?
• A replicated chromosome consist of two strands of
identical DNA called chromatids (sister chromatids)
chromatids
held together by a centromere.
chromosome
S phase: chromosomes replicate
chromatid
chromosome
chromatid
centromere
• When is a chromatid a chromatid?
Answer:
• A chromatid is a chromatid as long as it is
held in association with a sister chromatid at
the centromere.
centromere
centromere
chromatid
chromosome
chromatid
chromosome
P
R
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P
H
A
S
E
Longest phase of mitosis
• Centrioles move apart (not found in plants)
• Spindle fibers form and attach to centromeres
• Nuclear envelope breaks down, nucleolus disappears
C
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Mitosis: Interactive Java Tutorial
Click to animate the image.
D
A
Prophase
early prophase
late prophase
centrioles
spindle fibers
aster
fibers
nuclear envelope
disappearing
centromere
Question:
• What attaches the spindle fibers to the
centromeres?
Answer: Kinetochores
aster
fibers
centromere
centriole
spindle fiber
sister
chromatid
kinetochores
sister
chromatid
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• Shortest phase
• Centrioles travel to the
poles of the cell and
anchor with aster
fibers.
fibers
• Chromosomes move to
the metaphase plate
(equatorial plate center of cell).
Aster fibers
Spindle fibers
Metaphase plate
Metaphase
centrioles
aster
fibers
spindle fibers
metaphase plate
A
N
A
P
H
A
S
E
Problem
solving: How
does a
chromosome
move.
Centromeres separate
and spindle fibers
contract.
Sister chromatids
separate and move
apart.
After separation,
chromatids are now
considered
chromosomes.
chromosomes
A
N
A
P
H
A
S
E
Anaphase
No longer sister chromatids,
chromatids now chromosomes
aster
fibers
spindle fibers
centrioles
A
N
A
P
H
A
S
E
T
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L
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• Nuclear membrane and
nucleolus reappear.
• Chromosomes uncoil to
chromatin.
• In the end, two genetically
identical nuclei are present
• Cleavage furrow develops
in animal cells. Cell plate
develops in plants.
cell plate
T
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nuclear membrane reforming
nucleolus reappears
cleavage furrow (cytokinesis)
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Cytokinesis- after Mitosis
• Cytoplasmic division
• Cell plate complete in plants
• In the end, two separate daughter cells
produced with single nucleus.
cell plate
What phase is show in each micrograph above?
• If a plant cell undergoes mitosis, but no cell
plate if formed, what would be the result?
• Corn cells have 20 chromosomes. If it is
dividing mitotically, how many
chromosomes will be present at prophase,
metaphase and anaphase?
• A biologist studying corn roots (normally
20 chromosomes) locates one in late
telophase with only 19 chromosomes. How
might this have occurred?
Knowing When to Start/Stop
• Suppose you had a paper cut on your finger.
Although the cut may have bled and stung a
little, after a few days, it will have
disappeared, and your finger would be as good
as new.
1. How do you think the body repairs an injury, such as a
cut on a finger?
2. How long do you think this repair process continues?
3. What do you think causes the cells to stop the repair
process?
PROBLEM SOLVING
• Contact Inhibition
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.
Knowing
when to
stop
• Phases
• Check Points• What does G0
mean?
• What does this
mean for the
cell?
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PROBLEM SOLVING
Stem Cells
• http://www.sumanasinc.com/webcontent/
animations/generalscience.html
• http://www.dnalc.org/ddnalc/resources/st
em_cells.html
PROBLEM SOLVING
Stem Cells-
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PROBLEM SOLVING
PROBLEM SOLVING
PROBLEM SOLVING