Chapter 8
Difficult to transport
materials into, out of and
around the cell
Cell growth
Problems as the
cell gets bigger
As a cell grows its volume
increases at a faster rate than
surface area
Difficult for DNA
to direct the
function of the cell
Organisms grow by
increasing the number of
cells
Cell division replaces worn out
cells
Solution is cell division
Some organisms reproduce through cell
division
Cell division replaces damaged cells
Cells divide until they come into
contact with each other
Cell Growth and Division
Cells that continue to
grow even after contact
with each other is called
cancer
Can form a
mass of cells
called a tumor
Chapter 8
Chromosomes
Chromosome - structures in
the cell made of DNA and histones
which contains genetic information
Somatic cells - All of the cells in an
organism are somatic cells except
for the sperm and egg cells
Eukaryotic cells have
a nucleus which contains
the cell's DNA
Chromosome are distinct
lengths of DNA
Prokaryotic cells do
not contain a nucleus
One circular molecule of DNA
DNA is wrapped around
proteins called histones
Allows the DNA to fit
inside the nucleus
nucleosome - the combination of
DNA and a histone
Diploid (2n) - The total number
of chromosomes found in a
somatic cell
The number of chromosomes
varies from one species to another
Each pair of chromosomes
code for different traits
Humans have 23 pairs of chromosomes.
Therefore the diploid number for a human
is 46 chromosomes 2(23)
Cell Growth and Division
Homologous pair of chromosomes a pair of chromosomes which code
for the same traits
Chapter 8
Cell Division
The parent cell divides into
two daughter cells
The daughter cells are
exact duplicates of the parent
cell
Mitosis - When somatic cells
undergo cell division
The cell cycle
Interphase
G1
Cell grows and
functions normally
Cells such as nerve cells
are stuck in G1 and never
divide again.
DNA is replicated.
Two sister chromatids
attached at the centromere
S
Cell is committed
to completing mitosis
G2
Cell Growth and Division
Cell continues to grow.
Called G0
The centrosome in animal cells
have two centromeres
Organelles replicate
Found in plant and
animal cells
Centrosomes replicate
During cell division,
microtubules extend from the centrosome
Chapter 8
The cell cycle
The mitotic phase
Early prophase
Mitosis
Late prophase
Cytokinesis
Telophase
Metaphase
· Division of the
cytoplasm.
· Cleavage furrow for
· Nucleolus reforms.
animal cells
· Cell plate for plant · Nuclear envelope reforms.
· Chromosomes uncoil.
cells
Cell Growth and Division
Anaphase
· The nucleolus disappears
· The chromosomes begin to form into tight
coils.
· The mitotic spindle begins to form from
the centrosomes.
· The centrosomes begin to move away from
each other.
· The nuclear envelope breaks apart.
· The chromosomes continue to form tight
coils.
· The centrosomes move to opposite poles of
the cell and form a mitotic spindle.
· Some of the microtubules attach to the
chromosomes at the centromere.
· Some of the microtubules overlap with
microtubules from the opposite pole.
· The centromeres of the chromosomes
are lined up on the metaphase plate.
· The microtubules attached to the centromere
shorten separating the sister chromatids.
· The sister chromatids move to opposite poles
of the cell and are now considered individual
chromosomes.
· The microtubules that overlap move across
each other and lengthen the cell.