Mitosis Honors Biology

Cell Reproduction 2 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 cell More complex DNA is different in eukaryotic cells DNA comes in two forms o Chromatin – DNA and protein mass o Chromosome – linear strands of DNA o Each species has own # of chromosomes o Ex. Humans – 46 chromosome Dogs – 78 chromosomes Fruit 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 phases 1. Interphase 2. Mitotic phase 3. 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 cell 2. S phase – DNA gets replicated 3. 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 stages 1. prophase 2. prometaphase 3. metaphase 4. anaphase 5. 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

Mitosis plant 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 cycle 1. 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 points 1. G1 – if okay than enters S phase, if not goes to G0 (zero) and never divides 2. G2 check point – if ok enters M phase if not G0 phase 3. 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 tumors 2 types of tumors 1. benign – non cancerous 2. 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 body ex. Bone, muscle, etc

3. Leukemia blood forming tissue ex. Bone marrow 4. Lymphoma lymph 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 K1-9QB0http:// K1-9QB RQo0&feature=relatedhttp:// 480RQo0&feature=related

Mitosis out of control sIhDsok&feature=PlayList&p=95B92DD F5E02DF3A&index=44http:// sIhDsok&feature=PlayList&p=95B92DD F5E02DF3A&index=44

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