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Chapter 10
Cell Growth & Division
Section 10-1
Cell Growth
Read 1st Paragraph
Fig. 10-1
Limits To Cell Growth

2 reasons why cells divide rather
than get larger.
1. They don’t have enough DNA.
2. They can’t move enough nutrients &
wastes across the cell membrane.
DNA “Overload”

Remember:
• DNA control’s cell function.
• DNA is stored in the nucleus.

When a cell is small, the info in DNA
is able to meet the cell’s needs.
• But, as a cell increases in size, it doesn’t
make more DNA.

If it were to keep growing, there
would be an “Information Crisis”.
Cellular
DNA

Compare the DNA in the nucleus to
that of a small library.
• Read P. 241

Middle paragraph
Exchanging Materials


Recall that food, H2O, & O2 pass
through CM’s easily by passive &
active transport.
Waste also leaves the cell through
the cell membrane.

The rate at which these exchanges take
place depends on the surface area of the
cell.
• Surface area =Total area of the CM.

However, the rate at which food & O2 are
taken in, & wastes produced depends on
the cell’s volume.
• Volume =How much space is in the cell.
Surface Area –Volume Ratio

Imagine a cell shaped like a cube.
• P. 243, fig. 10-2
• Follow along!

Important things to note:
• Volume increases much faster than surface
area.


This causes the surface area-volume ratio to
decrease.
This causes serious problems for the cell.

http://plaza.ufl.edu/alallen/pgl/modu
les/rio/stingarees/module/why.html
Surface Area to Volume Ratio
Cell Size
Surface Area
(length x width x 6)
Volume
(length x width x height)
Ratio of Surface Area
to Volume

Use the street –traffic analogy.
• Read P. 242, bottom paragraph.

If a cell got too big, it would have
trouble getting enough O2 &
nutrients in, & waste out.
Division of the Cell

Before cells get too big they divide.
• Division creates 2 “daughter cells”.


This is called cell division.
Before cell division occurs, the cell
copies its DNA.
• This solves the problem of info
shortages.

Cell division also solves the volume
problem.
• By reducing size, the cell reduces
volume.
Cell Division
Section 10-2
Cell Division



Read p. 244 top para.
In pro-k’s, cell division is just the
splitting of the cell into 2 parts.
In eu-k’s, cell division is complex &
happens in 2 stages:
• Mitosis
• Cytokinesis
Prokaryotic Cell
Division

Reproduction through mitosis is
considered asexual.
• All the cells are identical to the parent
cell.
Chromosomes




In eu-k’s, genetic info is carried by
chromosomes.
Chromosomes are made of DNA & proteins.
Every org. has a certain # of chromosomes:
Ex:
• Fruit flies = 8
• Human cells = 46
• Carrot cells = 18

Chromosomes are normally visible
only during cell division.
• The rest of the time they are in a form
known as chromatin.

Before cell division happens,
chromosomes are copied.
• For this reason, each chromosome
consists of 2 identical “sister” chromatids.

Fig. 10-3

When cells divide, the “sister”
chromatids separate from each
other.
• 1 chromatid goes to each of the 2
new cells.

Chromatids are held together by a
centromere.
• Normally located @ the middle of the
chromatid.


Some can lie near the ends.
A human cell contains 46
chromosomes.
• Each consisting of 2 chromatids.
The Cell Cycle


Cell cycle –series of events that cells
go through as they grow & divide.
Interphase –period b/t cell divisions.
G1
The
Cell
Cycle
S
G2

During each cell cycle:
• A cell grows
• Prepares for division
• Divides to form 2 daughter cells
• P. 245, fig. 10-4

The cell cycle consist of 4 phases:
• G1 Phase
• S Phase
• G2 Phase
• M Phase
Events of the Cell Cycle

Most of a cell’s life is spent in interphase.

Interphase is divided into 3 phases:
• G1


Cells do most of their growing.
New proteins & organelles are also made.
•S


Chromosomes are copied.
Synthesis of DNA molecules takes place.
• G2


Shortest of the 3 phases.
Organelles & molecules required for cell division are
made.

When the G2 phase is done, the cell
is ready to enter the M phase.
• Aka = cell division
Mitosis

Divided into 4 phases:
• Prophase
• Metaphase
• Anaphase
• Telophase


Depending on the cell, mitosis can
last from minutes to days.
PMAT
Prophase

1st & longest phase.

Chromosomes become visible.

Centrioles separate & take up positions on
opposite sides of the nucleus.
• Centrioles -2 tiny structures located near the
nuclear envelope.

Spindle –a fanlike microtubule
structure that helps separate
chromosomes.
• Plant cells don’t have centrioles.

Near the end of prophase:
• Chromosomes coil more tightly.
• The nucleolus disappears.
• The nuclear envelope breaks down.
Prophase
Metaphase

2nd phase

Often lasts only a few minutes.


Chromosomes line up at the midline or
equator of the cell.
The centromeres of each chromosome
connect to the spindle.
Anaphase

3rd phase

During anaphase:
• The centromeres joining the sister chromatids,
separate & become individual chromosomes.
• These chromosomes then move to opposite
ends of the cell called poles.
• Anaphase ends when the chromosomes stop
moving.
Telophase



The 4th & final phase.
Chromosomes begin to disperse into a tangle of
dense material.
The nuclear envelope reforms around the
chromosomes.

The spindle breaks apart.

The nucleolus becomes visible again.
Cell Cycle
includes
G1 phase
Interphase
M phase
(Mitosis)
is divided into
is divided into
S phase
G2 phase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Cytokinesis –the division of the
cytoplasm.
• Cytokinesis usually occurs at the same
time as telophase.

It occurs in primarily 2 ways:
• By pinching off b/t the 2 daughter cells
equally.

Done in animal cells.
• By building a cell plate b/t the 2 cells.

Done in plant cells.
Mitosis Video

http://www.johnkyrk.com/mitosis.ht
ml
Section 10-3
Regulating the Cell Cycle

Note!
• Not all cells move through the cell cycle
at same rate.

Ex:
• Muscle cells & nerve cells don’t divide at
all, once they are developed.
• Skin cells, digestive cells, & cells in bone
marrow that make blood cells, divide
rapidly throughout our life.
• Rapidly dividing cells can pass through a
cell cycle every few hrs.
Controls of Cell Division



Refer to fig. 10-7 on p. 250
This illustration shows that cell
division can be turned on & off.
The same thing happens when we
have a cut in the skin or a broken
bone.
• New cells are made until the wound is
healed, then they stop dividing.
Fig. 10-7

Cells in a petri dish will continue to
grow until they come into contact w/
other cells.
Cell Cycle Regulators

In the 80’s, scientists dicovered what
controls the cell cycle.
• The substance was a protein called
cyclin.
• Cyclin regulates the cell cycle.

Since this discovery, scientists have
found other proteins that are
involved in the cell cycle.
• They call these proteins cyclins.

P. 251, fig. 10-8
Fig. 10-8
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.

There are 2 types of regulatory
proteins:
• Internal Regulators
• External Regulators
Internal Regulators



Made up of proteins that respond to
events inside the cell.
Allows the cell to only proceed when
certain events have happened.
Ex:
• Cells wont move to the next phase in
mitosis until all the right steps have
been completed.
External Regulators



Made up of proteins that respond to
events outside the cell.
They direct cells to speed up or slow
down the cell cycle.
Important during wound healing &
embryonic development.
Uncontrolled Cell Division


Cancer –a disorder in which some of
the body's own cells lose ability to
control growth.
Cancer cells don’t respond to the
signals that regulate the growth of
most cells.
• As a result they divide uncontrollably &
form masses of cells called tumors.

Tumors can damage surrounding tissues.
• Cancer cells can also move throughout
the body & cause serious problems, or
even death.

What can cause cancer?
• Tobacco

Smokeless or smoked
• Radiation



X-ray
UV
Radioactive
• Viral infections


HPV-cervical cancer
Another cause is a damaged gene in
a chromosome called the p53 gene.
• Damage to the p53 gene causes the cell
to lose the info needed to respond to
signals that would normally control their
growth.
Cell Cycle Game

http://nobelprize.org/educational_ga
mes/medicine/2001/cellcycle.html