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I. Background InfoA. Why Do Cells Divide?
1. Growth of organism2. Repair damaged cells3. Reproduction in microorganisms
B. Why are cells so tiny?1. To maximize the surface area to volume ratio.
What is the surface area and volume of a 4 cm cube?
h
w
d
Surface Area (SA) = (h) x (w) x (# of sides)
4 x 4 x 6 = cm2
Volume (V) = (h) x (w) x (d)
4 x 4 x 4 = cm3
SA/V =
96
64
3/2 or 1.5
What if we cut the cube into eight 2 cm cubes?
Volume 2 x 2 x 2 x 8 = cm3
Surface Area 2 x 2 x 6 x 8 = cm2
SA/VOL = 3
192
64
2. Having twice the surface area and the same volume allows for a more efficient exchange of materials (nutrients, wastes, O2, CO2 and H2O)
a) If a cell becomes too large it can’t transport materials across the membrane fast enough
3. DNA “Overload”a) Cell does not make more copies of DNA as
it grows; therefore the nucleus is limited in how much cell activity it can control
II. ChromosomesA. Chromosomes (DNA) carry all the genetic
information for the organism and are passed on from one generation to the next
B. Every species has a specific # of chromosomes (Human = 46, Chimp = 48, Mosquito = 6, Adder’s tongue fern = 1262)
C. Made up of chromatin1. Made of DNA twisted around histone
proteins.2. Compactly folded and coiled to form a
chromatid. Why?
Draw Fig. 10-3 pg. 244
D. Prior to division cells must duplicate their DNA Why?
E. Two identical “sister” chromatids are formeda) Attached by the
centromere
III. The Cell CycleB. Interphase
1. Cell’s nucleus and nucleolus are clearly visible.2. Chromosomes have not appeared.
3. Consists of 3 phases:a)G1 phase - cell growth right after cell divisionb)S phase - DNA replication c)G2 phase - replication of cell organelles (to
prepare for division) and synthesis of cell division structures
4. Cell spends ~90% of its time in interphase
C. Mitosis1. Prophase
a. Nuclear membrane, nucleus and nucleolus start to disappear
b. Chromosomes are clearly visible and are randomly arranged
c. Spindle fibers and centrioles appear (not in plants)
2. Metaphase
a. Chromosomes are lined up at the center of the cell (metaphase plate)
b. Done by attaching themselves to the visible spindle fibers
3. Anaphasea. The sister chromatids are pulled apart (at
the centromeres) to the opposite poles of the cell.
b. Each chromatid is a single chromosome.c. Each side gets an exact copy of each
chromosome.
4. Telophasea. Nuclear membrane, nucleus and nucleolus
reappears.
b. Chromosomes and spindle fibers start to disappear.
c. Mitosis is complete at this point.
D. Cytokinesis1. The completion of M phase where cell
organelles and cytoplasm are divided into two new cells.
2. In plant cells the Golgi bodies secrete a cell plate in the middle of the cell.
Mitosis Video Clip
Centrioles
Chromatin
Interphase
Nuclear envelope Chromosomes (paired
chromatids)
Prophase
Centromere
Spindle forming
Metaphase
Centriole
Spindle
Centriole
Anaphase
Individual chromosomes
Nuclear envelope reforming
Telophase
Cytokinesis
DRAW Fig. 10-5, pg. 246
IV. Regulating the Cell Cycle
A. Controls on Cell Division1. When cells come into contact with other cells
they respond by not growing (density dependent inhibition)
2. Controls on cell growth and cell division can be turned on and off
3. With an injury, cells at edge of injury are stimulated to divide rapidly to begin healing
B. Cell Cycle Regulators1. Cyclins are proteins that regulate the cell cycle
2. They signal when it is time for a cell to divide, duplicate their chromosomes, or enter another phase of the cycle
A sample of cytoplasm is removed from a cell in mitosis.
The sample is injected into a second cell in G2 of interphase.
As a result, the second cell enters mitosis.
C. Cancer1. Uncontrolled cell growth and division
2. Cells do not respond to regulatory signals
3. Malignant tumors are masses of cells that can damage surrounding tissue
4. When a cancer metastasizes, cells have broken off the tumor and traveled to other parts of the body
5. Known causes are smoking, tobacco, radiation exposure, and certain viruses
V. Stem CellsA. Three to five days after fertilization, a human
embryo is a mass of cells called stem cellsB. Stem cells are pluripotent, which means
they are not specialized and have the ability to differentiate (develop into any specialized cell, e.g. nerve cell)
C. Three current sources:1.Embryonic stem cells (discarded embryos
from fertility treatment)2.Umbilical cord blood3.Adult stem cells (bone marrow, heart, brain,
lungs)
D. Potential Treatments1.Alzheimer’s disease2.Heart disease3.Limb regeneration4.Organ transplants
http://www.pbs.org/wgbh/nova/sciencenow/3209/04.html