Download Cell Growth and Division

Why do cells divide rather than
continue to grow indefinitely?
Cell Growth and
Division
Chapter 10
Unicellular organisms
grow and then divide
into 2 organisms.
Multicellular organisms grow by division of
cells (increasing in number) rather than just
continually getting larger--Why?
1. DNA “Overload”- the number of
chromosomes (the amount of DNA) is
constant (there would not be enough
DNA to provide a really large cell with
enough new protein).
2. Laws of physics prevent cells from
growing too large
–
Diffusion rate
Limits to cell size – how basic
physics determines the rate of
diffusion in and out of a cell
1. Cell must be able to move materials in
and out of the cell
2. As cells increase in size
–
–
Volume increases faster than surface area
All exchanges occurs over the cell membrane
3. Decrease in surface area/volume ratio
–
Slows transport of materials
Section 10-1
Ratio of Surface Area to
Volume in Cells
Cell Size
Surface Area
(length x width x 6)
Volume
(length x width x height)
Ratio of Surface Area
to Volume
3X increase (side length) vs. 9X increase
(surface area) vs. 27X increase (volume)
Effect of cell size on diffusion
Small cell
Easy access to
the entire cell
for diffusion in
or out of the
cell.
Effect of cell size on diffusion
Even the
middle of the
small cell is still
accessed by
diffusion.
Effect of cell size on diffusion
large cell
Effect of cell size on diffusion
large cell – (with same
diffusion rate as small cell)
Related phenomena - As things get bigger
(whether it’s a single cell or a polar bear), volume
increases faster than surface area!
•
In zoology, Bergmann's Rule is a
principle that correlates
environmental temperature with
body mass in warm-blooded
animals. It asserts that within a
species, the body mass increases
with latitude and colder climate.
Among mammals and birds,
individuals of a particular species
in colder areas tend to have
greater body mass than
individuals in warmer areas. For
instance, White-tailed Deer are
larger in Canada than in the
Florida Keys. The rule is named
after a nineteenth-century
German biologist, Christian
Bergmann.
•
From Wikipedia
Related phenomena - Volume
increases faster than surface area!
•
Gigantothermy is a phenomenon with significance in biology and paleontology,
whereby large, bulky ectothermic (cold-blooded) animals are more easily able to
maintain a constant, relatively high body temperature than smaller animals by virtue of
their greater volume to surface area ratio. A bigger animal has proportionately less of
its body close to the outside environment than a smaller animal of otherwise similar
shape, and so it gains heat from, or loses heat to, the environment much more slowly.
•
The largest leatherback turtle ever found however was a little over three meters from
head to tail and weighed over 900 kilograms.
•
From Wikipedia
10 - 2
Cell Division
Cell Division
•The result of cell division is a pair
of identical “daughter” cells.
•Each daughter cell receives a full
set of genetic instructions (DNA).
Cell Division
Asexual
reproduction
Sexual
reproduction
• Three basic types
1) Binary fission
2) Mitosis
3) Meiosis
Prokaryotes
Eukaryotes
Reasons for Cell Division
1. To grow
• While keeping SA/V ratio high
2. Development
• Cell specialization
3. Repair and replace worn out cells
• homeostasis
4. Reproduction
• Continuity species/heredity
Cell Cycle
• Cell’s “life”
• Regulated by the organism
• Varies from:
– Species to species
– Cell types within an organism
• Divided into phases
– Interphase: period between divisions
– Mitosis: division of nucleus
– Cytokinesis: division of cell (cytoplasm)
C
Cell Cycle Outline
I. Interphase
A. G1 phase
B. S phase
C. G2 phase
II. Cell Division
A. Mitosis
1. prophase
2. metaphase
3. anaphase
4. telophase
B. Cytokinesis
mnemonic
Interphase
I___________
Prophase
P __________
Metaphase M __________
Anaphase
A __________
Telophase
T __________
Cytokinesis C _________
• A new cell grows G1
• It continues to grow as
it duplicates its
chromosomes S
• The cell grows more
G
2
and prepares for
mitosis
• The nucleus divides M
• The rest of the cell
divides (cytokinesis). C
• G0 is a cell not in the
cell cycle-a nondividing cell
G1 phase
S phase
G2 phase
Mitosis
Interphase
CELL CYCLE
Prophase
Metaphase
Anaphase
Telophase
Cell Division
Cytokinesis
How do cells make sure each daughter cell gets
a full and equivalent set of hereditary material?
• Chromosomes
– Chromosomes made of DNA and proteins
– Only visible as distinct (discrete) units during
cell division (they are in the chromatin form
for the rest of the cell cycle)
• All organisms have a specific number of
chromosomes
– Not related to complexity because of large
differences in size of chromosomes and other
factors.
DNA Architecture
• The DNA in a cell is
packed into an
elaborate, multilevel
system of coiling and
folding around proteins
• Chromatin is condensed
to form a chromosome
• A pair of replicated,
identical, and attached
chromosomes are called
sister chromatids
DNA double helix
Histones
“Beads
on a
string”
Nucleosome
Tight helical fiber
Supercoil
Sister
chromatids
Centromere
Figure 8.4
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Chromosomes
• Chromosomes are copied
in preparation of cell
division (S phase).
• The two halves are called
sister chromatids
• Held together by a
centromere
one chromosome
A chromatid
its sister chromatid
centromere
Sister chromatids
IDENTIFYING PHOTOGRAPHS OF
STAGES OF THE CELL CYCLE
Mitosis: division of the nucleus
interphase
metaphase
prophase
anaphase
metaphase
telophase
Interphase
chromatin
nucleus
Prophase:
chromosomes condense
nuclear envelope disappears
Spindle
fibers
Centriole
chromosomes
Figure 8.7x1c
Metaphase: chromosomes line up at the
equatorial plane
chromosomes
centriole
Spindle fibers
Figure 8.7x1d
Anaphase: sister chromatids separate and
are pulled to the poles
Figure 8.7x1e
Telophase: cytokinesis begins and ends,
nuclear envelope reappears
Cleavage furrow
New nucleus
Figure 8.7x1f
Cytokinesis
• Animals
• Cleavage furrow
• Plants
• Cell plate forms
between the new
nuclei
• New cell wall
• Cytokinesis
in animals
Cleavage
furrow
Cleavage furrow
Contracting ring of
microfilaments
(a) Animal cell cytokinesis
Daughter cells
Figure 8.8a
Wall of
parent cell
Cell plate
forming
Daughter
nucleus
• Cytokinesis
in plants
Vesicles containing
cell wall material
Cell plate
Cell wall
(b) Plant cell cytokinesis
New cell wall
Daughter cells
Figure 8.8b
Cytokinesis in plants
end