mitosis honors biology. cell reproduction 2 types 1. asexual 2. sexual
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Mitosis
Honors Biology
Cell Reproduction2 types
1. Asexual
2. Sexual
Asexual Reproduction• Duplication of all parts of the cell then splits into 2
• Cells are identical to each other
• Only 1 cell needed
• No genetic information exchanged
• Allows multicellular organisms to replace dead and dying cells pretty quickly
Sexual Reproduction• 2 parents
• genetic information exchanged
• Looks similar to parents llows maintenance of species and genetic variation
which is important for evolution.
Type of cell reproduction used depends on type of cell reproducing.
2 types of cells
1. Prokaryotic
2. Eukaryotic
Prokaryotic cells• Uses binary fission (asexual) reproduction
• Steps of binary fission:
• 1. DNA duplicated and moves to opposite side• 2. Cell elongates• 3. When cell reaches 2X its size, cell membrane
pinches inward, dividing cell into 2 daughter cells
Eukaryotic cellMore complexDNA is different in eukaryotic cells
• DNA comes in two formso Chromatin – DNA and protein masso Chromosome – linear strands of DNAo Each species has own # of chromosomes
o Ex. Humans – 46 chromosomeDogs – 78 chromosomesFruit fly – 3 chromosomes
Cell reproduction in eukaryotic cells can be asexual (Mitosis) or sexual (Meiosis)
Chromosome vs. chromatin• Add picture here
Mitosis (asexual reprod.)
• Cell Cycle = life cycle of a cell• Our body is made of trillions of cells that need to be
maintained and replaced.• To replace cells our current cells divide asexually
during a cell cycle
• Cell cycle consists of 3 phases1. Interphase2. Mitotic phase3. Cytokinesis
The Cell Cycle
Interphase
• 80 – 90 % of time spent here• cell doubles everything in cytoplasm and DNA
• 3 phases:
1. G1 phase – intense growth of cell2. S phase – DNA gets replicated3. G2 – final preparation for division and growth
Interphase
Mitotic phase (M phase)Mitosis - nuclear division of cell that results in 2
identical daughter cells.
5 stages1. prophase2. prometaphase3. metaphase4. anaphase5. telophase
Prophase“first phase”
• chromatin visible as sister chromosomes or dyads (paired homologous chromosomes)
• nucleoli disappears• centrioles separate and begin to form spindle fibers
• DYADS• Sister chromosomes (remember during Interphase DNA replicated so
now have 2 chromosomes)• Homologous chromosomes - carry same traits• Held together by centromere
Dyad / sister chromatid
Prophase
prophase
Prometaphase“before metaphase”• nuclear envelope breaks apart and disappears
• spindle fibers (microtubules) form from centrosome (at poles of cell)
• spindle fibers connect at kinetochore (part of centromere)
Metaphase• Centromeres of all chromosomes lined u in
middle of cell (equator or plate)
Metaphase
Metaphase in plants
Anaphase“apart phase”
• centromeres pulled apart into daughter chromosomes• cell elongates and furrow develops• daughter chromosomes pulled to opposite sides of
cell• spindle fibers shorten• complete when 1 set of chromosomes on opposite
side
Anaphase
Telophase“end phase”
• opposite of prophase• nuclear membrane forms around daughter
chromosome (46 in each human cell)• nucleoli reappears• spindle fibers disappear• 2 identical daughter cells• chromosomes uncoil and become less
distinguished
Telophase
Cytokinesis• occurs during end of telophase• equal division of cytoplasm• cell pinches into 2 cells
Mitosisplant vs. animal
• Instead of a furrow – a cell plate develops in plants
• Cell plate forms and grows outward eventually fusing with cell wall which splits cell into half, results in 2 daughter cells
• Remember plants lack centrioles, so don’t have spindle fibers either.
Control of cell cycle
• Some tissue undergo cell reproduction more frequently than others (skin and eye) and some not at all (nervous)
• Timing of cell division is different in different parts of the body
Ex. Hair goes through shedding and growth phases.
• Two things control the cell cycle1. Growth factors 2. Check points
Growth Factors (3)1. Anchorage dependence
• cells must be in contact with solid substance (extracellular matrix of tissue) to reproduce
2. Density dependent inhibition• when cells touch each other, they stop reproducing due to inhibition of
growth factor protein secretion
ex. Cutting skin frees up space and cells reproduce to replace skin cells lost
3. Growth Factor Proteins• proteins (cyclins) secreted by cells that stimulate other cells to grow. • When too crowded cells use up growth factor and stop growing
Check points• Check points check to make sure everything is going “as
planned”• Make sure cellular processes have been completed• Also receive messages from other cells to communicate
environmental conditions and give go ahead or stop growth.
3 check points1. G1 – if okay than enters S phase, if not goes to G0
(zero) and never divides2. G2 check point – if ok enters M phase if not G0 phase3. M check point – if Ok enters G1 phase
Mitosis and Cancer• Cancer cells don’t respond to cell cycle control system,
they just keep dividing uncontrollably.
• It only takes one cell to begin this process
• Our immune system normally recognizes abnormal cells and destroys them, but sometimes this doesn’t happen, then the cell divides out of control and forms a tumor.
2 Types of tumors2 types of tumors1. benign – non cancerous2. Malignant - cancerous (mal means bad)
If malignant, cells can break off the tumor, and spread throughout the system (via blood stream) and where ever the cancer cell settles, cancer sill also develop there. This process is called metastasizing.
• Cancer named according to the organ/tissue it originates
4 basic classifications of cancer
1. Carcinomas – external or internal coverings of the body
ex. Skin, intestines
2. Sarcomas – support tissues of bodyex. Bone, muscle, etc
3. Leukemiablood forming tissueex. Bone marrow
4. Lymphomalymph nodes, spleen (immune system)
Cancer cells continue to divide indefinitely as long as there is a nutrient supply unlike normal cells which are programmed to divide about 50 times.
Chemotherapy• Stops stages of mitosis, therefore stopping division of
not only cancer cells, but “normal cells” too
• Ex. Taxol, freezes spindle fibers so can’t divide,• Others stop spindle fibers from forming
• Side effects :• Nausea – due to fact that effecting intestinal cells• Hair loss – effects hair follicle cells, immune cells also
effected so can get sick very easily
Why undergo Mitosis?1. Replace old cells with same function and
structure
2. Growth of organisms
3. produce new identical organism (in less complex organisms)
When?• Human cells undergo mitosis on the
average of every 48 hours
Video links
• http://www.youtube.com/watch?v=VlN7K1-9QB0
• http://www.youtube.com/watch?v=nPG6480RQo0&feature=related
Mitosis out of control
• http://www.youtube.com/watch?v=_ZEysIhDsok&feature=PlayList&p=95B92DDF5E02DF3A&index=44
THE END
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