Mitosis Honors Biology. Cell Reproduction 2 types 1. Asexual 2. Sexual.

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

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