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Mitosis
The process of cell division occurs in a
series of stages or phases!!!
Limited cell size (reason they must divide)

DNA “overload”


Instructions found in the nucleus are
sufficient to meet all the cells’ needs
Exchanging Materials & Messages


All requirements must pass into the cell
through the membrane and all wastes must
pass out of the cell through the membrane
Surface Area-to-Volume Ratio


Want greater surface area compared to volume
Volume increases faster than does the surface area as
a cell gets larger
Cell division accounts for three
essential life processes:


Growth-happens because cells grow to a
maximum size, then divide
Repair-repairing tissues only happens
because of cell division


Repairing a tiny cut to regeneration of an arm
on a sea star
Reproduction- asexual and sexual
reproduction are dependent on cell division


Asexual, a whole new organism grows (mitosis)
Sexual, specialized cell division leads to
production of egg and sperm cells allowing this
to occur (meiosis)
Cell Cycle
These three
make up
Interphase
which is the
longest part of
the cell cycle





G1 = cell growth
S = (synthesis) DNA replication
G2 =some growth, preparation for
mitosis
M = mitosis (not a part of
interphase)
Cytokinesis
Interphase (G1, S, G2)

nucleolus
DNA starts as chromatin (long
threads), but then winds up into
chromosomes (coils) AFTER the copy
is made. Each chromosome and its copy
(sister) are attached and called sister
chromatids at the end of this phase.
-Area where the
sister chromatids
are joined.
Mitosis
Cell Division
 Prophase
 Metaphase
 Anaphase
 Telophase
Prophase




Centrioles appear and begin to move to
opposite ends of the cell.
Spindle fibers form between the centrioles.
Nuclear membrane starts to disappear.
Chromosomes condensed/nucleolus not
visible.
Centrioles
Spindle fibers
Metaphase



Chromatids (or pairs of chromosomes)
attach to the spindle fibers.
Centrioles are at poles.
Line up in middle
Anaphase

Chromatids separate and begin to be
pulled to opposite ends of the cell.
Telophase



Two new nuclei form
Chromosomes just begin to unwind
Cytoplasm pinches inward
Cytokinesis

In animal cells, the cell membrane pinches
inward to create two daughter cells – each
with its own nucleus
with identical
chromosomes.
• In plant cells, a structure known as the cell plate
forms midway between the divided nuclei
Mitosis in Actual cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
centrosome
has centrioles
Animal Cell
at Interphase
aster
duplicated
chromosome
20 µm
20 µm
MITOSIS
nuclear
envelope
fragments
spindle
pole
centromere
chromosomes at 20µm
metaphase plate
9 µm
daughter chromosome
20µm
kinetochore
cleavage furrow
16µm
nucleolus
chromatin
condenses
nucleolus
disappears
centrosome
kinetochore
spindle fiber
spindle
fibers forming
Early Prophase
Centrosomes have duplicated.
Chromatin is condensing into
chromosomes, and the nuclear
envelope is fragmenting.
polar spindle fiber
Prophase
Nucleolus has disappeared, and
duplicated chromosomes are visible.
Centrosomes begin moving apart,
and spindle is in process of forming.
Prophase
Nucleolus has disappeared, and
duplicated chromosomes are visible.
Centrosomes begin moving apart,
and spindle is in process of forming.
kinetochore
spindle fiber
Metaphase
Anaphase
Centromeres of duplicated chromosomes
are aligned at the metaphase plate (centerSister chromatids part and become daughter
chromosomes that move toward the spindle
of fully formed spindle). Kinetochore spindle
fibers attached to the sister chromatidspoles. In this way, each pole receives the same
come from opposite spindle poles.number and kinds of chromosomes as the parent cell.
Telophase
Daughter cells are forming
as nuclear envelopes and
nucleoli reappear. Chromosomes will
become indistinct chromatin.
lacks centrioles
Plant Cell
at Interphase
25µm
cell wall
chromosomes
6.2µm
spindle pole lacks
20µm
centrioles and aster
spindle fibers
6.2µm
6.2µm
cell plate
Animal cell(Early prophase, Prophase, Metaphase, Anaphase, Telophase): © Ed Reschke; Animal cell(Prometaphase): © Michael Abbey/Photo Researchers,
Inc.;
Plant cell(Early prophase, Prometaphse): © Ed Reschke; Plant cell(Prophase, Metaphase, Anaphase): © R. Calentine/Visuals Unlimited; Plant
cell(Telophase): © Jack M. Bostrack/Visuals Unlimited;
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6.6µm
Cell Cycle Control

Cells have very careful control over the cell
cycle:


To maintain quality of cells
Uncontrolled growth is Cancer
 Three environmental factors that cause
cancer are:
1.
cigarette smoke
2. air and water pollution
3. exposure to ultraviolet radiation from the
sun AND TANNING BEDS!!!
The Cell Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Interphase
G1 checkpoint
Cell cycle main checkpoint.
If DNA is damaged, apoptosis
will occur. Otherwise, the cell
is committed to divide when G
growth signals are present
0
and nutrients are available.
G
1
S
(growth and DNA
replication)
G1
(growth)
M
G2
(growth and final
preparations for
G
division)
2
M
M checkpoint
Spindle assembly
checkpoint. Mitosis
will not continue if
chromosomes are
not properly aligned.
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G2 checkpoint
Mitosis checkpoint.
Mitosis will occur
if DNA has
replicated properly.
Apoptosis will
occur if the DNA is
damaged and
cannot be repaired.
Apoptosis

Programmed cell death

Like the cell is committing suicide
Characteristics of Cancer Cells

Lack differentiation



Have abnormal nuclei




May be enlarged
May have abnormal number of
chromosomes
Extra copies of genes
Form tumors

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Are nonspecialized
Are immortal (can enter cell cycle
repeatedly)

Mitosis controlled by contact with
neighboring cells – contact inhibition
Cancer cells have lost contact inhibition
Characteristics of Cancer Cells

Undergo metastasis



Original tumor easily fragments
New tumors appear in other organs
Undergo angiogenesis

Formation of new blood vessels

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Brings nutrient and oxygen to tumor
Progression of Cancer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
New mutations arise, and one cell (brown) has the ability to start a tumor.
primary tumor
lymphatic
vessel
blood
vessel
Cancer in situ. The tumor is at its place of origin. One cell (purple)
mutates further.
lymphatic
vessel
blood
vessel
Cancer cells now have the ability to invade lymphatic and blood vessels
and travel throughout the body.
New metastatic tumors are found some distance from the primary tumor.
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Origins of Cancer: Oncogenes

Mutations in DNA repair mechanisms

Oncogenes




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Proto-oncogenes (when they are healthy)
promote the cell cycle in various ways
Tumor suppressor genes inhibit the cell
cycle in various ways
Both normally regulated in coordination
with organism’s growth plan
If either mutates, may lose control and
become oncogene (either one).
Origins of Cancer: Telomerase

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Chromosomes normally have special
material at each end called telomeres
(end parts)
These get shorter each cell division
When they get very short




Telomerase is an enzyme that adds
telomeres
Mutations in telomerase gene:

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The cell will no longer divide
Almost like running out of division tickets

Keeps adding new telomeres
Allow cancer cells to continually divide
Causes of Cancer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Heredity
growth
factor
growth factor
Activates signaling
proteins in a stimulatory
pathway that extends
to the nucleus.
receptor
protein
P
Viruses
oncogene
a. Influences that cause mutated proto-oncogenes
(called oncogenes) and mutated tumor
suppressor genes
P
P
Pesticides
and
herbicides
Radiation
sources
activated
signaling
protein
signaling
protein
Stimulatory
pathway
phosphate
b. Effect of growth factor
gene product
promotes
cell cycle
Inhibitory
pathway
gene product
inhibits
cell cycle
proto-oncogene
Codes for a growth factor,
a receptor protein, or a
signaling protein in a
stimulatory pathway.
If a proto-oncogene
becomes an oncogene,
the end result can be
active cell division.
c. Stimulatory pathway and
inhibitory pathway
tumor suppressor gene
Codes for a signaling
protein in an inhibitory
pathway. If a tumor
suppressor gene mutates,
the end result can be
active cell division.
d. Cancerous skin cell
d: © Biophoto Associates/Photo Researchers, Inc.
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1,100X
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r.
Cyclin- any
gene
involved in
regulating
the cell
cycle.
Normal cells obey strict rules.
Divide only when told.
Die rather than misbehave.
~Dr. Andrew Murray
Harvard University
If only students were like “normal
cells”.
~Dr. Tracey Schneeman
Streetsboro High School
Stem Cells


ADULT STEM CELLS
Many mammalian organs contain
stem cells

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EMBRYONIC STEM CELLS

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Retain the ability to divide
Aren’t totally differentiated
(specialized)
bone marrow stem cells divide to
produce various types of blood cells

Have the ability to become ANY type of
cell
Currently controversial


Therapeutic cloning to produce
human tissues can begin with
either adult stem cells or
embryonic stem cells
Embryonic stem cells can be used
for reproductive cloning, the
production of a new individual
Prokaryotic Cell Division

Prokaryotic chromosome is a ring of
DNA

1,000 X length of cell

Replicated into two rings prior to division


Binary fission


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Replicate rings attach to plasma
membrane
Splitting in two between the two
replicate chromosomes
Produces two daughter cells identical to
original cell – Asexual Reproduction
Binary Fission of Prokaryotes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
chromosome
1. Attachment of chromosome to
a special plasma membrane
site indicates that this
bacterium is about to divide.
cell wall
plasma
membrane
cytoplasm
2. The cell is preparing for binary
fission by enlarging its cell wall,
plasma membrane, and overall
volume.
200 nm
3. DNA replication has produced
two identical chromosomes.
Cell wall and plasma membrane begin to grow inward.
200 nm
4. As the cell elongates, the
chromosomes are pulled apart.
Cytoplasm is being distributed
evenly..
5. New cell wall and plasma
membrane has divided the
daughter cells.
200 nm
(All): © Stanley C. Holt/Biological Photo Service.
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January 30, 2008

Do you think all cells continue to
cycle through mitosis throughout
the entire life of a person? Are
there any cells that you think do?
Name them. Are there any cells
that you think do not? Name them.
(4 points)