Chapter 10: Cell Growth and
Division
Honors Biology/Chemistry
2013
Limits to Cell Growth
• As a cell grows larger:
– More demands are put onto the cell’s DNA.
– The cell has more trouble moving enough
nutrients and wastes across the cell
membrane.
• A cell’s functions are controlled by its
DNA.
• As a cell grows, it usually does not make
more DNA.
• If the cell were to grow continuously, it
would become too large for the DNA to
control...this is called “DNA Overload”.
• Materials such as food, oxygen, waste
and water pass in and out of a cell
through the cell membrane.
• The rate at which materials can pass
through the membrane depends on the
cell’s surface area.
• The rate at which food and oxygen are
used and waste is produced depends on
the cell’s volume.
• To maintain high efficiency, cells maintain a large
surface area to volume ratio.
• Imagining that cells are cube-shaped, look at the
example below:
Which value
increases most
rapidy?
How does the SA:V
ratio change as the
cell grows in size?
Division of the Cell
• Before a cell gets too large, it divides
forming two daughter cells.
• The process that forms two daughter
cells is called cell division.
Learning Check
• Give 2 reasons why cells divide.
• As a cell increases in size, which
increases more rapidly: its surface area
or its volume?
• Calculate the surface area to volume
ratio of a cube with 3 inch sides.
Cell Division
• Occurs differently in different organisms.
Prokaryotes
• Lack a nucleus and have a single
chromosome
• Reproduce using binary fission:
– Cells increase their cell mass slightly.
– DNA and cell components are replicated.
– Each cell divides into 2 new daughter cells.
Eukaryotes
• Go through a much more detailed cell
cycle, and divide using a process called
mitosis.
The Cell Cycle
• The time period during which a cell grows,
prepares for cell division, and divides to form
two daughter cells, each of which then begins
the cycle again.
• The cell cycle is broken into 2 large phases:
– Interphase: Period of growth and preparation for
division.
– M Phase (Cell Division): Mitosis and Cytokinesis
Interphase
• Prepares the cell to divide.
• Consists of 3 smaller phases:
– G1 : Cells increase in size and synthesize
new proteins and organelles.
– S: Chromosomes are replicated
– G2: Many organelles and molecules required
for division are produced.
• Once interphase is complete, the cell is
ready to enter cell division (M Phase).
M Phase
(Cell Division)
Mitosis
• Mitosis consists of 4 smaller phases:
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
Prophase
• First and longest phase of
Mitosis.
Spindle
forming
• Chromosomes condense and
become visible.
• Centrioles move to opposite
sides of the nucleus.
• Spindle appears.
• Nucleolus disappears.
• Nuclear envelope breaks down.
Centromere
Chromosomes
(paired
chromatids)
• Chromosomes are made up of DNA and protein.
• Before prophase, they are not visible because
their thin strands are spread throughout the
nucleus.
• During S phase, the chromosomes are
replicated.
– Once replication has occurred, each chromosome
consists of 2 “sister” chromatids, which are held
together at a centromere.
Metaphase
• Second phase of
mitosis.
• Chromosomes line up
across the center of
the cell.
• Spindles attach to the
centromere of each
chromosome, connecting
them to the centrioles
and holding them in
place.
Centriole
Spindle
Anaphase
• Third phase of mitosis.
• The centromeres split
allowing the sister
chromatids to
separate.
• Spindles pull the sister
chromatids to opposite
sides of the cell.
Individual
chromosomes
Telophase
• Final phase of Mitosis.
• Chromosomes unravel
• Nuclear envelopes
reform
• Nucleolus reappears
• Spindle begins to
break apart.
Cytokinesis
• Mitosis is considered to be the division
of the nucleus.
• After mitosis, two nuclei with identical
sets of chromosomes are present within
the cytoplasm of a single cell.
• Cytokinesis is the division of the
cytoplasm, which completes M Phase of
the cell cycle.
Cytokinesis
• Usually occurs simultaneously with telophase.
• In animal cells:
– The cell membrane is pulled inward until the
cytoplasm is pinched in equal parts.
• In plant cells:
– A “cell plate” forms midway between the two new
nuclei. The plate will eventually develop into a cell
wall dividing the two cells.
Learning Check
• Name the main events of the cell cycle.
• What happens during each stage of
interphase?
• What are chromosomes made of?
• At the completion of M Phase (Mitosis and
Cytokinesis), two identical daughter cells have
formed.
• These two daughter cells restart the cell cycle
at G1 of interphase.
Regulating the Cell Cycle
•Experiments show that normal cells will
continue to grow until they come into contact
with other cells.
•When cell’s come into contact with other cells,
they stop growing. This is called contact
inhibition.
•This demonstrates that cell growth and
division can be turned on and off.
Contact Inhibition
Copyright Pearson Prentice Hall
• Proteins called cyclins regulate the timing of
the cell cycle.
• Internal regulators: allow the cell to proceed
to the next phase of the cell cycle only when
certain processes have occurred inside the
cell.
– Example: These proteins will not allow a cell to
continue into G2until all chromosomes have been
duplicated during S phase.
• External regulators: speed up or slow down
the cell cycle depending on events outside of
the cell.
– Example: Contact inhibition
Uncontrolled Cell Growth
• Cancer is a disorder in which the body’s
own cells lose their ability to respond to
signals from internal and external
regulators.
• These cells divide uncontrollably and
form tumors.