Download Chapter 10 - North Mac Schools

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 cell membrane
(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 paragraph
In prokaryotes (pro-k), cell division is
just the splitting of the cell into 2
parts.
In eukaryotes (eu-k), cell division is
complex & happens in 2 stages:
1. Mitosis
2. Cytokinesis
Prokaryotic Cell Division

Reproduction through mitosis
is considered asexual.
All the cells are
identical to the
parent cell.
What are the resulting cells
called?
Chromosomes



In eukaryotes, genetic info is carried by
chromosomes.
Chromosomes are made of DNA & proteins.
Every org. has a certain # of chromosomes:
Examples:
•
•
•
•
•
Fruit flies = 8
Carrot cells = 18
Human cells = 46
Dog = 78
Sweet potato = 90

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 TWO
identical “sister” chromatids.
See p. 244, 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
(sometimes referred to as 23 pairs)
• 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.
During each cell cycle:
A cell grows
Prepares for division
Divides to form 2 daughter cells
p. 245, fig. 10-4
The
Cell
Cycle
G1
Consists of
4 phases:
G1 Phase
S Phase
G2 Phase
M Phase
S
G2
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. a.k.a. = 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.
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
https://www.youtube.com/watch?v=
TlYqh5OfJFk
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
fig.10-7


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 1980’s, scientists discovered
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 all 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 the 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 (inoculation available)
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://www.pinterest.com/pin/24537
5879673392966/
http://www.pinterest.com/pin/24537
5879673389251/
http://nobelprize.org/educational_ga
mes/medicine/2001/cellcycle.html
Stem Cells