Download Chapter 18 Cell Cycle

Cell Replication
Today we are going to look at how
cells reproduce. Cell Theory tells
us that all cells came from preexisting cells. Without replication
for growth, replacing damaged
cells, or for cells that have just died
life could not exist.
Prokaryotes
Most Prokaryotes (single cell without a
nucleus) reproduce Asexually through a
process called Binary Fission. The
Prokaryote replicates it’s DNA ring and
organelles and just splits in half so that each
half gets a complete identical copy of the
DNA. Bacteria and many other single cell
Protist reproduce this way and huge number
of cells can be produced this way quickly.
Bacteria and Organelles
Binary Fission Bacteria
Binary Fission
Paramecium and Amoeba
Eukaryotes
Cell division is more
complicated than in
Prokaryotes. For a Eukaryotic
cell to divide it must go through
the cell cycle: mitosis for
somatic cells and meiosis for
sex cells.
Cell Cycle
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Interphase
G1 The normal growth time for a cell as it
progresses toward DNA replication.
S
This is the time that DNA is replicated prior
to going into mitosis. Once DNA is duplicated
growth continues for a short time.
G2 The cell continues to grow and prepare for
Mitosis to begin. DNA checked for errors. A
process called APOPTOSIS kills the cell if the
DNA is not reproduced correctly.
Interphase
85% to 90% of the cells life is
spent in interphase.
Nerve cells and muscle cells
spend their whole life in
interphase.
Liver cells rarely divide.
Mitosis
vs.
Meiosis
Mitosis uses asexual reproduction to create
new somatic cells (body cells) for growth,
replacement worn out or damaged cells, and
reproduces 2 identical daughter cells. The
resulting cell is diploid (46 chromosomes just
like the mother cell).
Meiosis uses sexual reproduction to create
new sex cells (sperm or egg). Used to create 4
haploid ( gametes) sex cells each having 23
chromosomes. This is where genetic variation
is introduced.
Mitosis
The process where somatic cells
actually split and create two
“identical daughter cells.” Creating
two daughter cells is the total
reason for a cell go through mitosis.
It has four steps: Prophase,
Metaphase, Anaphase, and
Telophase. PMAT
Prophase
Is the first step of mitosis.
1. The nuclear envelope begins to
disappear.
2. Chromosomes begin to
condense.
3. Centrioles begin to move to
opposite sides of the cell.
Metaphase
Is the second step of mitosis.
1.The chromosomes line up at the
center of the cell.
2.Spindle fibers form from the
centrioles and attach to the
chromosomes at the centromere.
3.Most easily recognized stage.
Anaphase
Is the third step in mitosis.
1. The centrioles begin to pull the
spindle fibers toward the
opposite sides of the cell.
2. Chromosomes split ensuring the
exact DNA on either side of the
cell.
Telophase
Is the fourth phase of mitosis.
1. The nuclear envelope begins to
reappear.
2. The cell begins to pinch in the
center in preparation for separation.
3. Chromosomes begin to unwind in
the nucleus.
Mitosis
Mitosis ends at the end of
Telophase.
Cytokinesis
The cells actually divide and
begin to function as two
completely identical cells
beginning the G1 step of the
Cell Cycle. Two identical cells
is the result of mitosis.
Cytokinesis
In animal cells the cell is basically
“pinched in half” where a cell
furrow is created by the dividing
cytoplasm.
In plant cells the cell is separated by
growth of a cell plate that separates
the dividing cytoplasm.
Cell plate vs Cell Furrow
Plant or Animal Cell?
Comparison of Divisions
Mitosis
Meiosis
2
Number of
divisions
1
Number of
reproduced cells
2
4
Yes
No
Same as parent
Half of parent
Where
Somatic cells
Sex cells
When
Throughout life
At sexual maturity
Growth and
repair
Sexual reproduction
Genetically
identical?
Chromosome #
Role
31
Tumor
The uncontrolled division of
a somatic cell. This is why
cancer is such a hard
disease for doctors to cure;
Uncontrolled cell division