Cell Cycle
Does an animal get larger because each cell
increases in size or because it produces more of
them?
Cell Growth
• As you might have guessed, living things grow by
producing more cells.
• The koalas have the same size cells, just one has
more then the other.
Cell Growth
Mature red blood cells are not capable of dividing, as they do not possess nuclei.
Therefore, it is not possible that red blood cells will divide as they travel along our
blood vessels. New red blood cells are produced in the red bone marrow of long
bones in adults, not from the cell division of mature red blood cells.
"RBCs are terminally differentiated; that is, they can never divide. They live about
120 days and then are ingested by phagocytic cells in the liver and spleen."
Why DO Cell’s Divide ..
The reason cells divide is because as
volume increases:
•
•
•
•
More demand is placed on cell’s DNA (DNA
Overload)
More difficult to bring in enough nutrients
and get rid of waste (material exchange)
Ratio of surface area to volume
Overtime many of the cells die and need to
be replaced.
Chromosomes
• In eukaryotic cells, the genetic
information that is passed on from one
generation of cells to the next is carried
by chromosomes.
• The cells of every organism have a
specific number of chromosomes.
• Chromosomes contain both DNA and
protein tightly packed together to form
chromatin.
• Right before cell division each
chromosome is replicated, Each
chromosome consists of two identical
“sister” chromatids.
• When the cell divides, the “sister”
chromatids separate and go to each of
the new cells.
Chromosome
• Each pair of chromatids is attached at an area
called a centromere.
• Centromeres are usually located near the middle
of the chromatids, although sometimes can be
found at each end.
CELL CYCLE
• The process by which a cell reproduces to
create two identical copies is known as
mitosis.
• Cells formed by mitosis are known as daughter
cells.
• The cell division process occurs in several
different stages, known collectively as the 'cell
cycle'.
Cell Cycle
• The cell cycle consists of four stages  G1, S, G2, and
M and then cytokenesis.
• G1 and G2 are 'gap' phases.
• G1 (gap 1) phase (primary growth phase) –cell gets
bigger
• S phase is the synthesis phase in which the chromatin
(DNA) is copied (replicated).
• G2 (gap 2) –cell prepares to divide, organelles replicate
• M is the mitotic phase in which the cell physically
divides into two daughter cells. Has 4 sub-phases!
• Most cells are NOT actively dividing. These cells are in a
resting state (G).
• Mitosis (M phase) steps which include the
process for asexual cell division.
• Biologists divide the events of mitosis into
four phases:
- Prophase
- Metaphase
- Anaphase
- Telophase
Depending on the type of cell, the four phases
may last anywhere from a few minutes to
several days.
•
•
•
•
•
PROPHASE
The first and the longest phase of mitosis, prophase can take as much as 50 to 60
percent of the total time required to complete mitosis.
centrioles form and move to opposite ends
spindle fibers form
Chromosomes condense and become visible
nuclear membrane breaks down
METAPHASE
• chromosomes line up in
the middle of the cell
• Chromosomes attach to
spindle fibers
• The kinetochore is the
protein structure on
chromosomes where the
spindle fibers attach
during cell division to pull
the chromosomes apart.
• The kinetochore forms in
eukaryotes, assembles on
the centromere and links
the chromosome to
microtubule polymers
from the mitotic spindle
during mitosis and
meiosis.
ANAPHASE
• Sister chromatids separate and move toward opposite poles
• Each new chromatid is now called a
chromosome.
• (Hint if there is a centromere, it is a chromosome)
TELOPHASE
• Chromosomes gather at
opposite ends and start
to unwind
• Spindles break down
• Nuclear envelopes reform at the two poles
• New cell membranes
begin to form to create
two independent cells
CYTOKINESIS
the division of the cytoplasm to make two complete daughter cells
• ANIMAL CELLS
– Cell membrane pinches apart
into two equal parts with one
nucleus in each daughter cell
• PLANT CELLS
– Cell plate forms between two
nuclei
– Cell plate develops into a cell
wall
Animations
http://www.youtube.com/watch?feature=player_detailpage&v=VlN7K19QB0
http://www.johnkyrk.com/mitosis.html
http://www.hybridmedicalanimation.com/anim_mitosis.
html
Activity
• Pass out white boards to students (groups of
2-3)
• Flip through the following slides and have
students either draw or label the picture
PROPHASE
METAPHASE
CYTOKINESIS
ANAPHASE
Cell Cycle Regulators
• Scientists discovered that
cells in mitosis contain a
protein called cyclin when
injected in a non-dividing
cell, would cause a miotic
spindle to form.
• Cyclins regulate the timing
of the cell cycle in
eukaryotic cells.
• Many of the abnormal
traits of cancer cells are
due to defects in genes
that control cell division.
Uncontrolled Cell Growth
• Why is cell growth regulated so carefully?
• Cancer- a disorder in which some of the body’s
own cells lose the ability to control division.
Cancer cells do not respond to the signals that
regulate the division of most cells.