Mitosis The process of cell division occurs in a series of stages or phases!!!
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Transcript of Mitosis The process of cell division occurs in a series of stages or phases!!!
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Mitosis
The process of cell division occurs in a series of stages or phases!!!
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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
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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)
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Cell Cycle
G1 = cell growth S = (synthesis) DNA replication G2 =some growth, preparation for
mitosis M = mitosis (not a part of
interphase) Cytokinesis
These three make up Interphase which is the longest part of the cell cycle
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Interphase (G1, S, G2)
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.
nucleolus
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MitosisCell Division
ProphaseMetaphaseAnaphaseTelophase
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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
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Metaphase
Chromatids (or pairs of chromosomes) attach to the spindle fibers.
Centrioles are at poles. Line up in middle
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Anaphase
Chromatids separate and begin to be pulled to opposite ends of the cell.
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Telophase Two new nuclei form Chromosomes just begin to unwind Cytoplasm pinches inward
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Cytokinesis
• In plant cells, a structure known as the cell plate forms midway between the divided nuclei
In animal cells, the cell membrane pinches inward to create two daughter cells – each
with its own nucleus with identical chromosomes.
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Mitosis in Actual cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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;
Plant Cellat Interphase
centromere
aster
kinetochore
polar spindle fiber
chromosomescell wall25µm
centrosome
lacks centrioles
MIT
OS
IS
centrosomehas centrioles
Animal Cellat Interphase
nuclearenvelopefragments
chromatincondenses
nucleolusdisappears
Early ProphaseCentrosomes have duplicated.Chromatin is condensing into
chromosomes, and the nuclearenvelope is fragmenting.
ProphaseNucleolus has disappeared, and
duplicated chromosomes are visible.Centrosomes begin moving apart,
and spindle is in process of forming.
ProphaseNucleolus has disappeared, and
duplicated chromosomes are visible.Centrosomes begin moving apart,
and spindle is in process of forming.
20 µm duplicatedchromosome
20 µm
spindlefibers forming
spindlepole
9 µm
kinetochorespindle fiber
cleavage furrow
spindle fibers
20µm 16µm
kinetochorespindle fiber
AnaphaseSister chromatids part and become daughterchromosomes that move toward the spindle
poles. In this way, each pole receives the samenumber and kinds of chromosomes as the parent cell.
MetaphaseCentromeres of duplicated chromosomes
are aligned at the metaphase plate (centerof fully formed spindle). Kinetochore spindle
fibers attached to the sister chromatidscome from opposite spindle poles.
chromosomes atmetaphase plate
6.2µm6.2µm20µm6.2µmspindle pole lackscentrioles and aster
TelophaseDaughter cells are formingas nuclear envelopes and
nucleoli reappear. Chromosomes willbecome indistinct chromatin.
daughter chromosome 20µm
nucleolus
cell plate 6.6µm
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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 smoke2. air and water pollution3. exposure to ultraviolet radiation from
the sun AND TANNING BEDS!!!
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The Cell Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
G1
(growth)G0
G2 checkpointMitosis checkpoint.Mitosis will occurif DNA hasreplicated properly.Apoptosis willoccur if the DNA isdamaged andcannot be repaired.
S(growth and DNA
replication)
M
Cytoki
nesis
Telo
phase
An
ap
hase
Meta
ph
ase
Late
pro
phas
e
Prophase
Interphase
G1 checkpointCell cycle main checkpoint.If DNA is damaged, apoptosiswill occur. Otherwise, the cellis committed to divide whengrowth signals are presentand nutrients are available.
M checkpointSpindle assemblycheckpoint. Mitosiswill not continue ifchromosomes arenot properly aligned.
M
G2
G1 G2
(growth and finalpreparations for
division)
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Apoptosis
Programmed cell death Like the cell is committing suicide
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Characteristics of Cancer Cells Lack differentiation
Are nonspecialized Are immortal (can enter cell cycle repeatedly)
Have abnormal nuclei May be enlarged May have abnormal number of chromosomes Extra copies of genes
Form tumors Mitosis controlled by contact with neighboring
cells – contact inhibition Cancer cells have lost contact inhibition
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Characteristics of Cancer Cells
Undergo metastasis Original tumor easily fragments New tumors appear in other organs
Undergo angiogenesis Formation of new blood vessels
Brings nutrient and oxygen to tumor
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Progression of CancerCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
primary tumor
New mutations arise, and one cell (brown) has the ability to start a tumor.
Cancer in situ. The tumor is at its place of origin. One cell (purple)mutates further.
Cancer cells now have the ability to invade lymphatic and blood vesselsand travel throughout the body.
New metastatic tumors are found some distance from the primary tumor.
lymphaticvessel
bloodvessel
lymphaticvessel
bloodvessel
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Origins of Cancer: Oncogenes
Mutations in DNA repair mechanisms
Oncogenes 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).
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Origins of Cancer: Telomerase Chromosomes normally have special material
at each end called telomeres (end parts) These get shorter each cell division When they get very short
The cell will no longer divide Almost like running out of division tickets
Telomerase is an enzyme that adds telomeres Mutations in telomerase gene:
Keeps adding new telomeres Allow cancer cells to continually divide Like counterfeit tickets
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Causes of CancerCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
d: © Biophoto Associates/Photo Researchers, Inc.
activatedsignalingprotein
growthfactor
receptorprotein
signalingprotein
phosphate
b. Effect of growth factor
P
P
P
proto-oncogeneCodes for a growth factor,a receptor protein, or asignaling protein in astimulatory pathway.If a proto-oncogenebecomes an oncogene,the end result can beactive cell division.
tumor suppressor geneCodes for a signalingprotein in an inhibitorypathway. If a tumorsuppressor gene mutates,the end result can beactive cell division.
c. Stimulatory pathway andinhibitory pathway
1,100Xd. Cancerous skin cell
gene productpromotescell cycle
Stimulatorypathway
Inhibitorypathway
gene productinhibitscell cycle
growth factorActivates signalingproteins in a stimulatorypathway that extendsto the nucleus.
a. Influences that cause mutated proto-oncogenes(called oncogenes) and mutated tumorsuppressor genes
Heredity Radiationsources
Pesticides and
herbicides
Viruses
oncogene
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Animation
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Cyclin- any gene involved in regulating the cell cycle.
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Normal cells obey strict rules.Divide only when told. Die rather than misbehave.
~Dr. Andrew Murray Harvard University
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If only students were like “normal cells”.
~Dr. Tracey Schneeman Streetsboro High School
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Stem Cells ADULT STEM CELLS Many mammalian organs contain
stem cells Retain the ability to divide Aren’t totally differentiated
(specialized) bone marrow stem cells divide to
produce various types of blood cells EMBRYONIC STEM CELLS
Have the ability to become ANY type of cell
Currently controversial
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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
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Prokaryotic Cell Division Prokaryotic chromosome is a ring of DNA
1,000 X length of cell Replicated into two rings prior to division Replicate rings attach to plasma membrane
Binary fission Splitting in two between the two replicate
chromosomes Produces two daughter cells identical to
original cell – Asexual Reproduction
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Binary Fission of Prokaryotes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5. New cell wall and plasmamembrane has divided thedaughter cells.
1. Attachment of chromosome toa special plasma membranesite indicates that thisbacterium is about to divide.
2. The cell is preparing for binaryfission by enlarging its cell wall,plasma membrane, and overallvolume.
3. DNA replication has producedtwo identical chromosomes.Cell wall and plasma mem-brane begin to grow inward.
4. As the cell elongates, thechromosomes are pulled apart.Cytoplasm is being distributedevenly..
(All): © Stanley C. Holt/Biological Photo Service.
200 nm
200 nm
200 nm
chromosome
cell wall
plasmamembrane
cytoplasm
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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)