The Process of Cell
Growth & Division
Prokaryotic vs Eukaryotic Cells


Remember that prokaryotic cells are:

Smaller than Eukaryotic Cells

Simpler than Eukaryotic Cells
It turns out that their DNA is also:

Shorter than Eukaryotic Cells


3,000 vs 300,000 genes long
Organized into only 1 strand, while Eukaryotic
cells its organized into many

1 chromosome in a bacterium vs 46 in a
human
A closer look at Eukaryotic DNA
throughout the life of the cell…

Day-to-day the DNA is coiled around histone proteins into threads
called chromatin.

Before dividing the DNA replicates (makes an identical copy of itself).
The copy attaches to the original forming somewhat of an X like
structure. These copies are called chromatids.

When dividing the DNA coils even further into short rods called
chromosomes. These are so dense they can be easily seen through a
microscope.
The Process of Cell
Growth & Division
Growth (Interphase)

The period of cell growth is called interphase.

Interphase is composed of 3 parts: G1, S, G2
G1: Gap 1

Cell grows bigger and makes proteins needed
for life.

Cells can live their entire life growing. An example of this is
nerve cells in humans. They never progress past this part of
the cell cycle.

Most cells, though, will divide (reproduce) at some point.
Why would cells divide?
 Survival (they have become too big)
 DNA overload
 Cell Transport overload


Benefit of the larger organism
 Grow
 Heal
If a cell is going to divide it will continue through this
sequence…
S Phase: DNA Synthesis

During the S phase, the cell replicates its
DNA.

Remember the cell needs 2 complete sets
of DNA to divide into two daughter cells,
each with a complete copy of DNA.
G2: Gap 2

Cell grows even bigger and makes proteins
needed for two cells!

Once this is complete the cell is ready for
division!
4:30
Division

Division of the DNA

Prokaryotes divide in a process called Binary Fission.

Eukaryotes divide in a process called Mitosis.
Binary Fission (Prokaryotes)

DNA (chromosomes) segregate and move to
opposite sides of the cell.
Mitosis (Eukaryotes)

More complicated – must divide the entire contents of the
nucleus. For a human cell that is 46 chromosomes!

The cell MUST make sure that the DNA is divided evenly
so that EACH new cell has the correct instructions for life.

Because it is so important there are multiple steps…
The Four Steps of Mitosis
Mitosis is described as a series of
steps. The four steps are:
1.
Prophase
2. Metaphase
3. Anaphase
4. Telophase
The acronym
PMAT may help
you remember
the phases in
order!
Step 1 - Prophase

During prophase the nucleus prepares for division. There are 4 major events that occur in prophase. These events are
outlined below:

The DNA condenses and coils into chromosomes.

The nuclear membrane disappears.

Two organelles called centrioles move to opposite ends of the cell.

Threadlike spindle fibers stretch across the cell making a footballshaped network of fibers.
This is a picture of
a cell in prophase.
3:47
Step 2 - Metaphase

There are 2 major events that occur in metaphase. These events are
outlined below:

The replicated chromosomes line up at the center of the cell.

Each centromere becomes attached to a spindle fiber.
This is a picture of
a cell in
metaphase.
0:30
Step 3 - Anaphase

During anaphase the double stranded chromosomes in the center of the cell divide.
There are 3 major events that occur in anaphase. These events are outlined below:

Each centromere divides.

The sister chromatids separate.

Then, the separate chromatids begin to move away from each other
toward the opposite ends of the cell.
This is a picture of
a cell in
anaphase.
0:30
Step 4 - Telophase

Telophase is the last step in mitosis. There are 4 major events that occur in telophase.
These events are outlined below:

Centrioles and spindle fibers start to disappear.

The chromosomes stretch out and become harder to see.

A nuclear membrane forms around each mass of chromosomes.

A new nucleolus appears in each new nucleus.
This is a picture of
a cell in telophase.
Division of the Cell (Cytokinesis)
In both Prokaryotes and Eukaryotes it is called
cytokinesis.
Prokaryote
Eukaryote
Differs between
Animal
Plant
Cytokinesis in
Animal Cells
Cell’s membrane pinches
inward creating a cleavage
furrow. Eventually the two
sides touch resulting in two
separate daughter cells.
Cytokinesis in
Plant Cells
Cell’s membrane CAN NOT
pinch inward because of the
rigid cell wall. Instead, a cell
plate forms between the
two nuclei and slowly grows
into a new wall separating
the two daughter cells
1:13
The Cell Cycle
As you study, focus on learning
the steps of the Eukaryotic Cell
Cycle (right hand side)!
G1 phase
S phase
G2 phase
Cell Cycle in Onion Cells
interphase
prophase
anaphase
metaphase
Telophase / cytokinesis
Can You Find Cells in the Different
Phases of the Cell Cycle?
The End