Mitosis

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Mitosis
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A little Vocabulary . . .

• Mitosis division of the nucleus in autosomal
  cells
• Autosomal Cells
• all cells except sex cells

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More Vocabulary

• Meiosis division of nucleus to
  produce gametes in sex cells
• Sex Cells cell that produce gametes
  Ex sperm/egg
• Chromotid one of the 2 parts of
  a duplicated chromosome.
• sister chromatids

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Vocab continued

• Chromatin granular substance
  in the nucleus
• contains DNA and proteins called histones
• Chromosome threadlike structure contains genetic
  information
• Condense to from X-shaped structures
• Centromere central part of chromosome where
  chromatids attach

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Genes and Proteins

• Proteins do the work of the cell
• growth, maintenance, response to the environment,
  reproduction, etc.
• Proteins are chains of amino acids.
• The sequence of amino acids in each protein is
  coded in the DNA as a specific sequence of A, C,
  G and T bases a gene.
• Each gene codes for a different protein.

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Genes and Proteins Continued

• Key points
• All cells in an organism have the same genes.
• What makes cells different from each other is
  that different genes are turned on and turned off
  in different cells.
• The DNA must be copied and then divided exactly
  so that each cell gets an identical copy.

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Mitosis

• Cells divide to make more cells. While all the
  other organelles can be randomly separated into
  the daughter cells, the chromosomes must be
  precisely divided so that each daughter cell gets
  exactly the same DNA.
• Humans have 46 chromosomes, 23 from each parent.
  Every cell has the same 46 chromosomes Each
  species has a characteristic number of
  chromosomes corn ahs 20, house flies have 10,
  chimpanzees have 48.

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Mitosis and Meiosis!

• Mitosis is normal cell division, which goes on
  throughout life in all parts of the body.
• Meiosis is the special cell division that creates
  the sperm and eggs, the gametes. We will discuss
  meiosis separately.
• Mitosis and meiosis occur in eukaryotes.
• Prokaryotes use a different methodnuclear
  fission to divide.

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Chromosomes

• Chromosomes are very long strands of DNA.
• contain genetic information
• Needed to create and run an organism.
• DNA takes 2 forms
• spread out like spaghetti in a bowl
• proteins cause the DNA to become tightly
  condensed into an X-shaped chromosome
• Each chromosome has a central constricted region
  called a centromere that serves as an attachment
  point for the machinery of mitosis.

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More Chromosomes

• Chromosomes exist in 2 different states
• Before DNA replication
• chromosomes have one chromatid.
• After DNA replication
• chromosomes have 2 sister chromatids, held
  together at the centromere.
• Each chromatid is one piece of DNA with its
  supporting proteins.

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• In mitosis, the two chromatids of each chromosome
  separate, with each chromatid going into a
  daughter cell.
• Remember! diploid cells have two copies of each
  chromosome, one from each parent. These pairs of
  chromosomes are NOT attached together.

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Cell Cycle

• Some cells divide constantly
• cells in the embryo, skin cells, gut lining
  cells, etc.
• Other cells divide rarely or never-only to
  replace themselves.
• Actively dividing cells go through a cycle of
  events that results in mitosis.
• Most of the cycle is called interphase.
• During interphase the cell increases in size, but
  the chromosomes are invisible.
• The 3 stages of interphase are called G1, S, and
  G2.

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Interphase

• G1 (Gap) is the period between mitosis and S,
  when each chromosome has 1 chromatid.
• Cells spend mot of their time in G1.
• Growth and normal funtion
• The S phase (Synthesis)
• DNA replication
• the chromosome goes from having one chromatid to
  having 2 chromatids held together at the
  centromere.
• G2 (Gap) is the period between S and mitosis.
• The chromosome have 2 chromatids, and the cell is
  getting ready to divide.

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Machinery of Mitosis

• Chromosomes are pulled apart by spindle fibers,
  which are made of microtubules.
• Spindle fibers are attached to each centromere (a
  part of the chromosome), and anchored on the
  other end to a centrosome
• 2. There are 2 centrosomes, one at each end of
  the cell.
• 3. The chromosomes are lined up in the middle
• 4. When the spindle fibers contract, the
  chromosomes are pulled to the opposing poles.

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Stages of Mitosis!

• Prophase
• Metaphase
• Anaphase
• Telophase
• Just remember PMAT!

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Prophase

• Division Begins!
• 1. The chromosomes condense.
• The proteins attached to the DNA cause the
  chromosomes to go from long thin structures to
  short fat one, which makes them easier to pull
  apart.
• The nuclear envelope disappears.
• The centrosomes move to opposite poles.
• During interphase, the pair of centrosomes were
  together just outside the nucleus. In prophase
  they separate and move to opposite ends of the
  cell.
• 4. The spindle starts to form, growing out of the
  centrosomes towards the chromosomes.

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Metaphase

• Chromosomes are lined up on the equator
• The centrosomes are at opposite ends and the
  spindle fibers attached to the centromeres.
• Everything is aligned for the rest of the
  division process to occur.

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Anaphase

• Centromeres divide.
• Each individual chromosome goes from
• 1 chromosome with 2 chromatids
• to
• 2 chromosomes with one chromatid each.
• Spindle fibers contract, and the chromosomes are
  pulled to opposite poles.

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Telophase

• In telophase the nucleus actually divides.
• The chromosomes are at the poles of the spindle.
• The spindle disintegrates
• The nuclear envelope re-forms around the two sets
  of chromosomes.

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Summary of Mitosis

• Prophase
• Chromosomes condense
• Nuclear envelope disappears
• centrosomes move to opposite sides of the cell
• Spindle forms and attaches to centromeres on the
  chromosomes
• Metaphase
• Chromosomes lined up on equator of spindle
• centrosomes at opposite ends of cell
• Anaphase
• Centromeres divide each 2-chromatid chromosome
  becomes two 1-chromatid chromosomes
• Chromosomes pulled to opposite poles by the
  spindle
• Telophase
• Chromosomes de-condense
• Nuclear envelope reappears
• Cytokinesis the cytoplasm is divided into 2 cells

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Cytokinesis

• Organelles division
• NOT a part of mitosis!!!!
• Different in plants and animals!
• In plant cells
• a new cell wall made of cellulose forms between
  the 2 new nuclei,
• Cell membranes form along the surfaces of this
  wall.
• When the new wall joins with the existing side
  wall, the 2 cells have become separate.
• In animal cells
• a ring of actin fibers forms around the cell
  equator and contacts, pinching the cell in half.

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Cancer

• uncontrolled cell division.
• It starts when a single cell that loses its
  control mechanisms due to a genetic mutation.
  That cell starts dividing without limit, and
  eventually kills the host.
• Normal cells are controlled by several factors.
• Normal cells stay in the G1 stage of the cell
  cycle until they are given a specific signal to
  enter the S phase, in which the DNA replicates
  and the cell prepares for division. Cancer cells
  enter the S phase without waiting for a signal.
• Normal cells are mortal. This means that they
  can divide about 50 times and then they lose the
  ability to divide, and eventually die. This
  clock gets re-set during the formation of the
  gametes. Cancer cells escape this process of
  mortality they are immortal and can divide
  endlessly.
• Normal cells that suffer significant chromosome
  damage destroy themselves due to the action of a
  gene called p53. Cancer cells either lose the
  p53 gene or ignore its message and fail to kill
  themselves.

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Cancer Progression

• There are many different forms of cancer
• Mutations in genes called ONCOGENS
• The normal oncogenes provide control mechanisms
  for the cell.
• mutations are caused by radiation, certain
  chemicals and various random events during DNA
  replication.
• Once a single cell starts growing uncontrollably,
  it forms a tumor, a small mass of cells.
• No further progress can occur unless the
  cancerous mass gets its own blood supply.
• Angiogenesis is the process of developing a
  system of small arteries and veins to supply the
  tumor. Most tumors dont reach this stage.
• A tumor with a blood supply will grow into a
  large mass.
• Eventually some of the cancer cells will
  metastasize- they break loose and move through
  the blood supply to other parts of the body,
  where they start to multiply.
• It occurs because tumor cells lose the proteins
  on their surface that hold them to other cells.

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Cancer Treatment

• Two basic treatments surgery to remove the
  tumor, and radiation or chemicals to kill
  actively dividing cells.
• It is hard to remove all the tumor cells. Tumors
  often lack sharp boundaries for easy removal, and
  metastatic tumors can be very small and anywhere
  in the body.
• Radiation and chemotherapy are aimed at killing
  actively dividing cells, but killing all dividing
  cells is lethal you must make new blood cells,
  skin cells, etc. So treatment must be carefully
  balanced to avoid killing the patient.
• Chemotherapy also has the problem of natural
  selection within the tumor. If any of the tumor
  cells are resistant to the chemical, they will
  survive and multiply. The cancer seems to have
  disappeared, but it comes back a few years later
  in a form that is resistant to chemotherapy.
  Using multiple drugs can decrease the risk of
  relapse its hard for a cell to develop
  resistance to several drugs at the same time.