Transcript Cell Division

Cell Division and
the Cell Cycle
Importance of Cell Division
• Replace dead or damaged cells
• It is much easier to transport nutrients
to smaller cells than larger cells
• Growth (bones etc.)
• Reproduction (meiosis)
• Chromatid – 1 strand of duplicated
chromosome
• Centromere – structure that holds
chromatids together
• Spindle fiber – protein structures that
guide chromosomes toward centrioles
during cell division
• Chromatin – a combination of protein and
DNA
Cell Division
• Despite great differences in the forms
and structures of living things, most
cells show remarkable similarities in
the manner in which they divide. Cell
division occurs in very primitive
organisms, like bacteria, to extremely
complex multi-cellular organisms, like
humans.
• Mitosis – is a type of cell division in
which daughter cells receive the
same number of chromosomes as
the parent cell.
Stages of Cell Division
• Cell division is a continual process that goes
through 2 distinctive stages to create two
identical cells. The first stage is the division of
the cell’s nucleus, this is called mitosis. The
second stage is the division of the cytoplasm,
which is called cytokinesis.
Mitosis
• Mitosis is divided into 4 phases; prophase,
metaphase, anaphase, and telophase.
• The length of time each phase takes
depends on the type of cell that is dividing.
• Mitosis may take a few minutes up to
several days.
Prophase
• The nuclear membrane
dissolves and the
chromosomes become visible
as they shorten and thicken.
• The centrioles separate and the
pieces move to the opposite
poles.
• Spindle fibers begin to grow
from the centrioles and attach to
the centromere of the
chromatin.
• The two sister strands of
chromatin are held together by
the centromere.
Metaphase
• The chromosomes
move towards the
center of the cell and
are then pulled into a
straight line by the
spindle fibers.
Anaphase
• The centromeres divide and
the sister chromatids (or
chromosomes) move to
opposite poles of the cell.
• Anaphase is finished once
the chromosomes stop
moving.
• If mitosis proceeds correctly,
the same number of
chromosomes will be found
at each pole.
Telophase
• Chromosomes reach the poles
of the cell and once again begin
to lengthen and intertwine. The
spindle fibers dissolve and the
nuclear membrane begins to
form around each group of
chromosomes. Finally,
cytokinesis begins.
Cytokinesis
• Cytokinesis is the division of the
cytoplasm and all of its organelles.
• This generally takes place at the
same time as telophase.
• In plant cells, the separation is
accomplished by a cell plate that
forms between the two
chromosome masses. This cell
plate will develop into a new cell
wall.
• The more elastic animal cells
pinch off in the center as the
cytoplasm moves to opposite
poles.
The Cell Cycle
• The cell cycle is the series of events that
cells go through as they grow and divide.
• During the cell cycle, a cell grows,
prepares for division, and divides to form
two daughter cells, each of which then
begins the cycle again.
• The cell cycle is made up of 4 phases; M,
S, G1, and G2 phases.
Events of the Cell Cycle
• Mitosis and cytokinesis make up the M phase of
the cell cycle.
• The M phase occurs quite quickly, where as
interphase can be very long in comparison.
• Interphase is divided into 3 phases; G1, S, and
G2.
– G1phase – cells grow and make new proteins and
organelles.
– S phase – chromosomes replicate, DNA molecules
are synthesized, and proteins associated with DNA
are also made during this phase.
– G2 phase – organelles and molecules required for cell
division are made. Now the cell is ready to enter the
M phase and start the process of cell division.
• The Cell Cycle –
Prentice Hall
• Page 249
1. Most white blood cells are only needed
for a short period of time so they don’t
have to have a long life span.
2. Neither heart or nerve cells can divide so
injuries cannot heal through production of
new cells. Smooth muscle can divide so
injuries can heal through cell division.
3. As a result of mechanical and chemical
digestion the cells making up the digestive
tract are more apt to be damaged or
destroyed in these processes.
4. If cancer cells were on the table their life
span would be “long lived” and cell division
would be “seemingly unlimited.”