Transcript Where Do Cells Come From?

Where Do Cells Come From?
“All cells come from pre-existing
cells” -Cell Theory
 3 types of cell divisions:
 Mitosis-nuclear cell division
in somatic cells, asexual
reproduction
 Meiosis-nuclear cell division
in germ cells, sexual
reproduction
 Prokaryotic Fission-cell
division in bacteria cells,
asexual reproduction
Review of Terms used in Mitosis/Meiosis
 Somatic cells-all cells except sex
cells
 Germ cells-sex cells, sperm and
eggs
 Diploid-2 of every chromosome
 Haploid-1 of each chromosome
 Chromosome-a linear
arrangement of genes, composed
of DNA
 How many chromosomes are
found in humans?
 Which cells are diploid and
haploid in humans?
Review of Terms used in
Mitosis/Meiosis
 Chromatid-1 arm of
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duplicated chromosome, sister
chromatids
Centromere-area on
chromosome that holds
chromatids together
Histones-proteins associated
with chromosomes, organize
structure
Nucleosome-1 unit of DNA +
8 histones
Chromatin-all DNA +
histones + other proteins
Eukaryotic Cell Cycle
 Interphase-3 phases
 G1-initial growth, G0 resting phase, permanently arrested
 S-synthesis, DNA is duplicated
 G2-final preparations before mitosis, microtubule formation
 Mitosis-4 phases: Prophase, Metaphase, Anaphase, Telophase
 Cytokinesis-division of cytoplasm
Most adult cells are in
what phase of the
cell cycle?
Control of the Cell Cycle
 Tightly regulated, require signals
 Cyclins required for cells to move from
G1S, G2M
 In mammalian cells p53 stops cycle if
DNA is damaged, hasn’t finished
replicating, or if chromosomes are not
attached to spindle
 High levels result in apoptosis 
programmed cell death through
caspases
Mitosis
 Produces 2 identical diploid daughter cells from 1
parent cell
 Have the same DNA  clones
 Used for growth and repair
 Asexual reproduction used by some members of fungi,
plants, animals, protists
Mitosis-PMAT
Prophase
 Chromosomes
condense
 Nucleolus disappears,
nuclear envelope
breaks apart
 Centrioles duplicate,
move to opposite poles
 Microtubules grab
chromosomes in order
to move them
 Longest phase
Mitosis-PMAT
 Metaphase-
microtubules align
chromosomes at the
equator of a cell,
“metaphase plate”
 Kinetochore spindle
fibers attached to
sister chromatids
come from poles
Mitosis-PMAT
 Anaphase-pulling apart of
chromatids/centromeres,
microtubules contract,
moving chromatids to
opposite poles, “spindle
apparatus” is clearly visible
 Shortest phase
 Telophase-chromosomes
decondense, nuclear
envelope reforms, nucleolus
reappears
Cytokinesis
 Division of cytoplasm
 Occurring simultaneously
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with telophase
Occurs differently in plant
and animal cells
Cell plate formationPlant cells
Vesicles from golgi align at
equator and fuse to form
cell wall
Cleavage FurrowingAnimal Cells
Actin filaments align at
equator (contratile
ring)and contract until
separate cell into two
Stem Cells and Cloning
 Stem cells adult cells that retain ability to divide
 Can differentiate into different types of cells
 Therapeutic cloning  produces human tissues
 Reproductive cloning  new individual can be made
Cloning and Embryonic Stem Cells
 Embryonic Stem Cells (ES)-cells from an early embryo;
these cells have not received the genetic instructions to
become a specialized cell yet
 These cells can be transferred into a organ and become that
type of tissue. Example: ES cells  defective pancreas,
become pancreas cells and start producing insulin
Stem Cell Lines
 100s have already been created that are heart, liver,
pancreas, etc. cell lines
 Eventually, transplant into humans; mice studies are
very promising
Problems:
 immune reaction
 Getting the cells to defective tissue
 Ethical issues (no fertilized egg required)
Properties of Cancer Cells: loss of cell cycle control
(When Compared to Normal Cells)
 Additional chromosomes,
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genes
Grow and divide
abnormally (faster)
Less adhesive, don’t stick
to each other
Metastasize-migrate to
other locations
Don’t communicate with
each other
Don’t apoptose (die)
Cancer
 Unregulated and
uncontrolled cellular
growth
 Form tumors
 Metastasize
Cancer: Loss of Genetic Controls
over Cells
 Cell growth and repair is
tightly regulated by genes;
when these genes fail 
Cancer
 Proto-oncogene
(accelerator) normal
growth gene becomes
mutated  oncogene,
BRCA1
 Tumor suppressor genes
(brakes) -control cell
death, ex. p53 gene
Causes of Cancer
 UV, X-ray, gamma
radiation, chemicals in
work places, smoking
 Viruses  Hepatitis C, 
liver cancer, HPV 
genital warts cervical
cancer
 Chromosome
translocation leukemia
 Carcinogens-cancer
causing agents, ex.
Compounds found in
cigarettes
Cancer : Tumors and Treatment
 Benign-slow growth, no metastasis, not
lethal unless size becomes large
 Malignant-rapid growth, metastasize,
destroy tissue around them
Treatment
 Chemotherapy-targets quickly dividing cells,
both cancer and healthy
 Radiation Therapy-high energy radiation
targets only tumor
Prokaryotic Cell Division
 Binary fission
 Asexual reproduction
 No nucleus, only
nucleoid region
 Single circular
chromosome
 Cell wall