Limits to Cell Growth
• The larger a cell becomes, the more
demands the cell places on its DNA
and more trouble the cell has
moving enough nutrients and
wastes across the cell membrane
Growing Cells
1µ
2µ
3µ
4µ
6
5µ
6µ
How are surface area and volume
affected by growth
Size
/ µm
1
2
3
4
5
6
Surface
area
/ µm2
6
24
54
96
150
216
Volume
/ µm3
1
8
27
61
125
216
SA/V
6
3
2
1.5
1.2
1
DNA “Overload”
• In Eukaryotic Cells, DNA is found in the
nucleus
• As a cell increases in size, it does not make
extra copies of DNA
• “Information Crisis” would occur if a cell was to
grow without limit
• In time, the cell’s DNA would no longer be able
to serve the increasing needs of the growing
cells
DNA “Overload”
• There is another reason why the size of cells are
limited.
• The rate of exchange depends on the surface
area of the cell.
• The total area of its Cells Membrane
• Rate at which food and oxygen are used and
waste products are produced depends on a cell’s
volume
DNA “Overload”
• Volume increases much more rapidly then
the surface area
• It would be more difficult for a larger cell to
get oxygen and nutrients in and waste
products out.
Cell Division
Process by which a cell divides into two daughter
cells
• Before it becomes too large, a growing cell
divides forming two “ Daughter” cells
• The cell replicates, or copies its DNA
• Each daughter cell receives its own genetic
“library”
Chromosomes
• Genetic information is passed on by
chromosomes
• Chromosomes are made up of DNA and
Proteins
• Cells of every organism have a specific number
of chromosomes
• Chromosomes are not visible except during
cells division
• Chromosomes condense at the beginning of
cell division
Chromosomes
• Each chromosome s is replicated before cell
division because of this, each chromosome
consists of two identical “Sister” chromatids
Chromatids
• Attach at the centromere located near the
middle of the chromatids
Cell Cycle
• A series of events that cells go through as
they grow and divide
• During the cell cycle, a cell grows, prepares
for division, and divides to form tow
daughter cells, each of which then begins
the cycle again
Mitosis
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• Biologists divide the events of mitosis into
phases:
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase
Mitosis in Action
Blue shows DNA, Green shows
spindle fibers
Interphase
• Has three phases: G1, S, & G2
• G1 – Cells do most of their growing
• S- Chromosomes are replicated and the
synthesis of DNA molecules take place
• G2 – shortest phase organelles and
molecules required for cell divisions are
produced
Prophase
• The longest and first phase
• Chromosomes becomes visible
• Centrioles separated and take up positions
on opposite sides of the nucleus
• Centrioles help organize the spindle:
– Fan like microtubule structure that helps
separate the chromosomes
Metaphase
• The second phase
• Chromosomes line up across the center of
the cell
Anaphase
• The third phase
• He centromeres separate allowing the sister
chromaids to separate
Telophase
• The final phase
• The chromosomes begin t disperse into a
tangle of dense material
• A nuclear envelope reforms
• Spindle begins to break apart
• Nucleolus becomes visible
• Mitosis is complete
Cytokinesis
• Division of the cytoplasm itself
• Occurs at the same time as telophase
Cell Cycle Regulators
• Cyclin
– Protein that regulates the cell cycle
– Regulate the timing of the cell cycle in
Eukaryotic cells
Internal Regulators
• Protein that respond to events inside the
cell are called Internal Regulators
External regulators
• Proteins that respond to events outside the
cell are called external regulators
• Direct cells to speed up or slow down the
cell cycle
Uncontrolled Cell Growth
• Cancer
– A disorder in which some the body’s own cells
lose the ability to control growth
– Cancers cells do not respond to the signals that
regulate the growth of most cells
– As a result, they form masses of cells called
Tumors that can damage for surrounding
tissues.
Cancerous Tumor