Chapter
8: Cell Growth and Division
Section 8-1: Cell Growth
Ø
In most
instances, a living thing grows because it produces more and more cells.
o
The cells in a
human being are very similar in size to those in an ant.
§
Does growth
have to occur in this way?
·
Can an organism
get larger just by increasing the size of its cells?
Ø
Recall Chapter
5: Cell membranes allow food, waste, and other chemicals into
and out of the cell.
o
Cell function
depends on the cell membrane.
See
Figure 8-2 Page 160
o Volume increases quicker than surface area.
· After a certain point, the volume of the cell becomes too large for the surface area to function.
o Compare this volume/surface area problem to an office building.
§ A cell can undergo an “information crisis” due to size.
o DNA is copied to mRNA to accomplish tasks.
§ DNA is copied in finite and rated amounts.
· As a cell increases in size, the number of tasks increases.
§ Its like trying to run an accounting firm with one calculator.
Ø
The cell solves
the information crisis by dividing.
o
CELL DIVISION-
Is a process by which one cell divides into two daughter cells.
Ø
Cells can grow
and divide at astonishing rates.
o
Referred to as
J_CURVE growth or exponential growth.
Ø
E. coli can
double in volume and divide every ½ hour.
o
After 1 day one
E. coli bacterium can divide into 14-Kg worth
o
After 3 days
one E. coli cN divide into enough bacteria to outweigh to Earth.
Ø
These optimum
conditions can only be reached in short spans because they are always checked by
limits in food, space, and increasing waste.
Ø
One of the most
amazing aspects of cell life in multicellular organisms is how closely cell
growth and development are controlled.
o
Some cells
never divide or they divide rarely.
§
Cardiac muscle
and nervous tissue
o
Some cells
divide rapidly and constantly.
§
Skin cells and
digestive tract.
Ø
Scientists
observe controlled cell growth in culture dishes.
o
Culture dishes
with cells placed in it will have cells grow until the cells take up all space.
§
Cells will stop
growing when they come into contact with each other.
Ø
Controls on
cell growth can be turned on and off.
o
During injury
cells @ the site of the problem are stimulated to grow and divide.
§
Starts the
healing process.
o
When healing
process is near completion, the process slows down.
Uncontrolled
Cell Growth
Ø
The
consequences of uncontrolled cell growth is severe.
o
Cancer is a
disorder in which cells have lost their ability to control their growth.
§
Cancer cells
placed in a culture dish will grow and grown until all space and food is
depleted.
·
Cells then die
due to lack of necessities.
Section 8-2: Cell Division: Mitosis
and Cytokinesis
Ø
Division of
eukaryotic cells occurs in two stagres.
o
Mitosis and
cytokinesis
Ø
MITOSIS is the
process by which the nucleus of the cell is divided into two nuclei.
o
Each has the
same # and type of chromosomes as the parent cell.
Ø
CYTOKINESIS is
the process by which the cytoplasm divides, thus forming two distinct cells.
Ø
These processes
are complex due to the cells complexity.
o
DNA is a
complex molecule therefore the copying process will be complex.
§
Copying of DNA
must be perfect of daughters cells will die or be cancerous.
Chromosomes
Ø
Recall chapter
5: CHROMOSOMES are structures that contain the genetic
information.
o
Chromosome
means “colored body”
§
Chromosomes
contain genetic information in the form of DNA.
§
Prokaryotic
cells have long circular chromosomes.
§
Eukaryotic
cells have chromosomes of distinct lengths of DNA.
·
Humans have 46
chromosomes.
Composition of Chromatin
Ø
Chromosomes are
made up of a material called CHROMATIN.
o
Between cell
divisions, chromatin is dispersed in condensed regions throughout the cell.
o
During cell
division, the chromatin condenses and the chromosomes become visible.
Ø
Chromatin is
composed of DNA and protein.
o
The protein is
used to coil the DNA so that it fits inside the nucleus.
§
The DNA unwound
is 10,000X longer than the chromosome!
o
Protein is
HISTONE.
§
Discovered by
Don and ADA Olins and Christopher Woodcock.
o
Together the
DNA and HISTONES form bead-like structures called NUCLEOSOMES.
§
Nucleosomes
coil around each other to form chromosomes.
CHROMOSOME
STRUCTURE
o
After DNA
replication, the chromosome becomes visible.
§
This is the
beginning of MITOSIS.
o
The chromosome
contains two CHROMATIDS, or identical parts.
§
Sister
chromatids.
o
Joined together
at a sight called CENTROMERE.
§
Usually near
the center of the chromatids.
o
Each human cell
contains contains 46 chromosomes each of which consists two chromatids.
CHROMOSOME
STRUCTURE
o
After DNA
replication, the chromosome becomes visible.
§
This is the
beginning of MITOSIS.
o
The chromosome
contains two CHROMATIDS, or identical parts.
§
Sister
chromatids.
o
Joined together
at a sight called CENTROMERE.
§
Usually near
the center of the chromatids.
Each
human cell contains contains 46 chromosomes each of which consists two
chromatids.