The Process of Cell

Growth & Division

Prokaryotic vs Eukaryotic Cells Remember that prokaryotic cells are:Remember that prokaryotic cells are:

Smaller than Eukaryotic CellsSmaller than Eukaryotic Cells

Simpler than Eukaryotic CellsSimpler than Eukaryotic Cells

It turns out that their DNA is also:It turns out that their DNA is also:

Shorter than Eukaryotic CellsShorter than Eukaryotic Cells

3,000 vs 300,000 genes long3,000 vs 300,000 genes long

Organized into only 1 strand, while Eukaryotic Organized into only 1 strand, while Eukaryotic cells its organized into manycells its organized into many

1 chromosome in a bacterium vs 46 in a 1 chromosome in a bacterium vs 46 in a humanhuman

A closer look at Eukaryotic DNA A closer look at Eukaryotic DNA throughout the life of the cell…throughout the life of the cell…

Day-to-day the DNA is coiled around histone proteins Day-to-day the DNA is coiled around histone proteins into threads called into threads called chromatin. chromatin.

Before dividing the DNA replicates (makes an identical Before dividing the DNA replicates (makes an identical copy of itself). The copy attaches to the original forming copy of itself). The copy attaches to the original forming somewhat of an X like structure. These copies are called somewhat of an X like structure. These copies are called chromatids.chromatids.

When dividing the DNA coils even further into short When dividing the DNA coils even further into short rods called rods called chromosomeschromosomes. These are so dense they . These are so dense they can be easily seen through a microscope.can be easily seen through a microscope.

The Process of Cell

Growth & Division

Growth (Interphase)Growth (Interphase)

The period of cell growth is called The period of cell growth is called interphaseinterphase. .

Interphase is composed of 3 parts: G1, S, G2Interphase is composed of 3 parts: G1, S, G2

G1: Gap 1G1: Gap 1 Cell grows bigger and makes proteins Cell grows bigger and makes proteins

needed for life.needed for life.

Cells can live their entire life growing. Cells can live their entire life growing. An example of this is An example of this is nerve cells in humans.nerve cells in humans. They never progress past this part of They never progress past this part of the cell cycle. the cell cycle.

Most cells, though, will divide (reproduce) at some point. Most cells, though, will divide (reproduce) at some point. Why would cells divide?Why would cells divide? Survival (they have become too big)Survival (they have become too big)

DNA overloadDNA overload Cell Transport overloadCell Transport overload

Benefit of the larger organismBenefit of the larger organism GrowGrow HealHeal

If a cell is going to divide it will continue through this If a cell is going to divide it will continue through this sequence…sequence…

S Phase: DNA SynthesisS Phase: DNA Synthesis

During the S phase, the cell During the S phase, the cell replicates its DNA.replicates its DNA.

Remember the cell needs 2 Remember the cell needs 2 complete sets of DNA to divide into complete sets of DNA to divide into two daughter cells, each with a two daughter cells, each with a complete copy of DNA. complete copy of DNA.

G2: Gap 2G2: Gap 2 Cell grows even bigger and makes Cell grows even bigger and makes

proteins needed for two cells!proteins needed for two cells!

Once this is complete the cell is ready Once this is complete the cell is ready for division!for division!

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DivisionDivision

Division of the DNADivision of the DNA Prokaryotes divide in a process called Prokaryotes divide in a process called Binary Binary

Fission.Fission.

Eukaryotes divide in a process called Eukaryotes divide in a process called Mitosis.Mitosis.

Binary Fission (Prokaryotes)Binary Fission (Prokaryotes) DNA (chromosomes) segregate and DNA (chromosomes) segregate and

move to opposite sides of the cell.move to opposite sides of the cell.

Mitosis (Eukaryotes)Mitosis (Eukaryotes) More complicated – must divide the entire More complicated – must divide the entire

contents of the nucleus. For a human cell that contents of the nucleus. For a human cell that is 46 chromosomes! is 46 chromosomes!

The cell MUST make sure that the DNA is The cell MUST make sure that the DNA is divided evenly so that EACH new cell has the divided evenly so that EACH new cell has the correct instructions for life. correct instructions for life.

Because it is so important there are multiple Because it is so important there are multiple steps…steps…

The Four Steps of MitosisThe Four Steps of Mitosis

11. Prophase. Prophase

2. Metaphase2. Metaphase

3. Anaphase3. Anaphase

4. Telophase4. Telophase

Mitosis is described as a series of steps. The four steps are:

The acronym PMAT may

help you remember the

phases in order!

Step 1 - ProphaseStep 1 - Prophase During prophase the nucleus prepares for division. There are 4 major events that occur in prophase. During prophase the nucleus prepares for division. There are 4 major events that occur in prophase.

These events are outlined below:These events are outlined below:

The The DNA condenses and coils into chromosomesDNA condenses and coils into chromosomes.. The The nuclear membrane disappearsnuclear membrane disappears.. Two organelles called Two organelles called centrioles centrioles move to opposite ends of move to opposite ends of

the cellthe cell. . Threadlike Threadlike spindle fibers stretch across the cellspindle fibers stretch across the cell making a making a

football-shaped network of fibers.football-shaped network of fibers.

This is a picture of a cell in prophase.

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Step 2 - MetaphaseStep 2 - Metaphase

There are 2 major events that occur in metaphase. These events There are 2 major events that occur in metaphase. These events are outlined below:are outlined below:

The The replicated chromosomes line up at the centerreplicated chromosomes line up at the center of of the cell. the cell.

Each Each centromere becomes attached to a spindle fibercentromere becomes attached to a spindle fiber..

This is a picture of a cell in metaphase.

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Step 3 - AnaphaseStep 3 - Anaphase During anaphase the double stranded chromosomes in the center of the cell 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 divide. There are 3 major events that occur in anaphase. These events are outlined below:outlined below:

Each centromere dividesEach centromere divides. .

The The sister chromatids separatesister chromatids separate. .

Then, the Then, the separate chromatids begin to move away from each otherseparate chromatids begin to move away from each other toward the opposite ends of the cell.toward the opposite ends of the cell.

This is a picture of a cell in anaphase.

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Step 4 - TelophaseStep 4 - Telophase Telophase is the last step in mitosis. There are 4 major events that occur in Telophase is the last step in mitosis. There are 4 major events that occur in

telophase. These events are outlined below:telophase. These events are outlined below:

Centrioles and spindle fibers start to disappearCentrioles and spindle fibers start to disappear. . The The chromosomes stretch out chromosomes stretch out and become harder to see. and become harder to see. A A nuclear membrane forms around each mass of nuclear membrane forms around each mass of

chromosomes.chromosomes. A new nucleolus appears in each new nucleus.A new nucleolus appears in each new nucleus.

This is a picture of a cell in telophase.

Division of the Cell (Cytokinesis)Division of the Cell (Cytokinesis)

In both Prokaryotes and Eukaryotes it is called In both Prokaryotes and Eukaryotes it is called cytokinesis.cytokinesis.

ProkaryoteProkaryote

Animal Plant

Eukaryote

Differs between

Cytokinesis Cytokinesis in Animal in Animal CellsCells

Cell’s membrane pinches Cell’s membrane pinches

inward creating a cleavage inward creating a cleavage

furrow. Eventually the two furrow. Eventually the two

sides touch resulting in two sides touch resulting in two

separate daughter cells.separate daughter cells.

Cytokinesis Cytokinesis in Plant in Plant CellsCellsCell’s membrane CAN NOT pinch Cell’s membrane CAN NOT pinch

inward because of the rigid cell inward because of the rigid cell

wall. Instead, a cell plate forms wall. Instead, a cell plate forms

between the two nuclei and between the two nuclei and

slowly grows into a new wall slowly grows into a new wall

separating the two daughter cellsseparating the two daughter cells

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The Cell CycleThe Cell Cycle

As you study, focus on As you study, focus on learning the steps of the learning the steps of the

Eukaryotic Cell Cycle Eukaryotic Cell Cycle (right hand side)!(right hand side)!

S phase

G1 phase

G2 phase

Cell Cycle in Onion CellsCell Cycle in Onion Cells

interphase prophase metaphase

anaphase Telophase / cytokinesis

Can You Find Cells in the Can You Find Cells in the Different Phases of the Cell Different Phases of the Cell Cycle?Cycle?

The End