Download Cell Growth Chapter 10 PPT

Limits to Cell Growth
 The 2 reasons cells divide rather than continue to
grow indefinitely are-
 The demands on the cells DNA become too great
and the DNA may “overload” (refer to the library
analogy)
 The rate of food/oxygen consumption and waste
production is directly related to the cells volume.
This exchange occurs through the cell membrane,
(surface area). The surface area of a cell does not
increase at the same rate as the volume does if the
cell simply continues to grow.
Ratio of Surface Area to Volume
 Cube 1cm x 1cm x 1cm has a Surface area of 6cm2
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and a volume of 1cm3. Ratio is 6:1
Cube 2cm x 2cm x 2cm: Surface area=24cm2,
Volume of 8cm3. Ratio is 3:1
Cube 3cm x 3cm x 3cm: Surface area = 54 cm2,
Volume of 27cm3. Ratio is 2:1
Bottom line: as the cube (cell) increases in volume,
the surface area does NOT keep up accordingly.
This causes a big problem when the cell relies on
the cell membrane for materials exchange.
Refer to the Town/highway analogy
Surface area to volume ratio
Cell Division
 When a cell divides into 2 cells, this is called cell
division and produces 2 “daughter” cells
 Before this happens, all of the DNA must be copied to
provide the new cell with information
 Cell division also solves another problem. That it
keeps the surface area/volume ratio to a reasonable
level.
Chromosomes
 Chromosomes are made up of DNA, and are
responsible for all of a cells genetic information
 The cells of every organism have a specific number of
chromosomes. (cells of fruit flies-8 chromosomes,
cells of carrots-18 chromosomes, cells of humans-46
chromosomes)
 Prior to cell division, each chromosome is replicated.
 During this process, the chromosomes become visible
and consist of 2 identical “sister” chromatids attached
to a centromere
Sister Chromatids attached to a
centromere
Cell Cycle-the series of events that a cell
goes through as they grow and divide
 During the cell cycle, the cell grows, prepares for
division, and divides to form 2 daughter cells, each of
which goes through the same steps.
Interphase
 G1 phase-the cells does most of it’s growing in G1
 In G1, cells increase in size and synthesize new
proteins and organelles
 Next is the S phase. In the S phase, chromosomes are
replicated and the synthesis of DNA occurs
 G2 phase follows after S phase is completed. G2 is the
shortest of the parts of Interphase.
 During G2, many organelles and molecules required
for cell division are produced.
Mitosis-divided into 4 phases
Phase 1-Prophase
 Prophase-first and longest phase of mitosis (50-60% of
the time of mitosis is spent here)
 Centrioles become visible
 Centrioles lie in a region called the centrosome that
helps in organizing the spindle. The spindle helps
separate choromsomes
 At the end of prophase, the chromosome become
more tightly coiled, the nucleolus disappears and the
nuclear membrane breaks down
nd
Metaphase-2
phase of mitosis
 Metaphase lasts only a few minutes
 Chromosomes line up across the center of the cell
 Microtubules connect the centromere of each
chromosome to the poles of the spindle
rd
Anaphase-3
phase of mitosis
 Centromeres that join sister chromatids separate,
allowing chromatids to separate and become
individual chromosomes
 Chromosomes continue to separate into 2 groups near
the poles of the spindle
 Anaphase is over when the chromosomes stop moving
th
Telophase-4
and final mitotic
phase
 Chromosomes begin to disperse
 Nuclear envelope re-forms around each chromosome
cluster
 Spindle begins to break apart
 Nucleolus becomes visible in each new daughter cell
nucleus
 Mitosis in complete, but cell division is not complete
Cytokinesis
 The cytoplasm of the cell must separate
 The cytoplasm is “pinched off” in 2 nearly equal parts
 In plant cells a cell plate forms midway between the 2
new nuclei
How long does cell division take?
 Sea urchin cells-2 hours
 Many plant & animal cells-8-10 hours
 Bean cells-19 hours
 Mouse cells-22 hours
 Human nerve and RBC never divide
How long do cells live?
 Lining of esophagus:2-3 days, (can divide)
 Lining of small intestine:1-2 days, (can divide)
 Lining of large intestne:6 days (can divide)
 RBC: Less than 120 days (cannot divide)
 WBC: 10 hours to decades (cannot divide)
 Smooth muscle: long lived (can divide)
 Cardiac (heart) muscle: long lived (cannot divide)
 Skeletal muscle: long lived (cannot divide)
 Neuron(nerve cell) long lived (most do not divide)
Controls of Cell Division
 Cyclins are proteins in cells that regulate the timing of
the cell cycle in eukaryotic cells
 Internal regulators are proteins that respond to events
inside the cell
 External regulators are proteins that respond to events
outside the cell
Uncontrolled cell growth
 Certain cells do not respond to the signals that
regulate cell growth.
 Tumors are masses of cells that can damage
surrounding tissue.
 Cancer may result when cells break loose from
tumors, spread throughout the body, disrupting
normal activities, causing serious problems
potentially.
Normal cells compared to cancer
cells
Stem Cells
 All cells in the human body come from one original cell
 The first few daughter cells can potentially
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differentiate into any type of body cell
Most cells become differentiated prior to birth
Once a cell becomes differentiated, it cannot change
what it is (skin cells remain skin cells, etc)
Non-specialized cells that can become other types of
cells are called stem cells
Stem cells can be used to grow other cells needed for
repair in the body
http://www.kqed.org/quest/television/view/326?gclid
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Stem Cells