Section 6-2Section 6-2

The Cell CycleThe Cell Cycle

The Cell Cycle Describes the Life The Cell Cycle Describes the Life of a Eukaryotic Cellof a Eukaryotic Cell

Cell division in eukaryotic cells is more Cell division in eukaryotic cells is more complex than in prokaryotic cells because complex than in prokaryotic cells because it involves dividing both the cytoplasm and it involves dividing both the cytoplasm and the chromosomes inside the nucleus.the chromosomes inside the nucleus.

Also have to correctly rearrange Also have to correctly rearrange organelles to form two properly functioning organelles to form two properly functioning cells.cells.

The Cell CycleThe Cell Cycle

The The cell cyclecell cycle is a repeating sequence of is a repeating sequence of cellular growth and division during the life cellular growth and division during the life of an organismof an organism

A cell spends 90% of its time in the first A cell spends 90% of its time in the first three phases of the cycle – called three phases of the cycle – called interphaseinterphase

The cell only enters the last two phases of The cell only enters the last two phases of the cell cycle if it is about to divide.the cell cycle if it is about to divide.

Five Phases of the Cell CycleFive Phases of the Cell Cycle

1.1. First Growth Phase or GFirst Growth Phase or G11

• During this phase, a cell grows rapidly and During this phase, a cell grows rapidly and carries out its routine functions. carries out its routine functions.

• This phase occupies the majority of most This phase occupies the majority of most cell’s life.cell’s life.

Five Phases of the Cell CycleFive Phases of the Cell Cycle

2.2. Synthesis Phase or SSynthesis Phase or S• The cell’s DNA is copied during this phase.The cell’s DNA is copied during this phase.• At the end of this phase, each chromosome At the end of this phase, each chromosome

consists of two chromatids attached to the consists of two chromatids attached to the centromere.centromere.

Five Phases of the Cell CycleFive Phases of the Cell Cycle

3.3. Second Growth Phase or GSecond Growth Phase or G22

• Preparations are made for the nucleus to Preparations are made for the nucleus to divide.divide.

• Microtubules are assembled and used to Microtubules are assembled and used to move the chromosomes during mitosis.move the chromosomes during mitosis.

Five Phases of the Cell CycleFive Phases of the Cell Cycle

4.4. MitosisMitosis• Process during cell division in which the Process during cell division in which the

nucleus of a cell is divided into two nuclei.nucleus of a cell is divided into two nuclei.• Each nucleus ends up with the same Each nucleus ends up with the same

number and kinds of chromosomes as the number and kinds of chromosomes as the original cell.original cell.

Five Phases of the Cell CycleFive Phases of the Cell Cycle

5.5. CytokinesisCytokinesis

The process during cell division in which The process during cell division in which the cytoplasm divides. the cytoplasm divides.

The Cell CycleThe Cell Cycle

The Cell Cycle is Carefully The Cell Cycle is Carefully ControlledControlled

How do cells know when to divide? How is How do cells know when to divide? How is the cell cycle controlled?the cell cycle controlled?

Cells have a system that controls the Cells have a system that controls the phases of the cell cycle.phases of the cell cycle.

Similar to a set of “red-light-green-light” Similar to a set of “red-light-green-light” switches that are regulated by feedback switches that are regulated by feedback information from the cell.information from the cell.

Has key checkpoints or inspection points Has key checkpoints or inspection points at which feedback signals from the cell at which feedback signals from the cell can trigger the next phase of the cell cycle can trigger the next phase of the cell cycle ((green lightgreen light).).

Other feedback signals can delay the next Other feedback signals can delay the next phase to allow for completion of the phase to allow for completion of the current phase (current phase (yellowyellow or or redred light). light).

Controlled by proteinsControlled by proteins

Principle Checkpoints of the Cell Principle Checkpoints of the Cell CycleCycle

1.1. Cell Growth Checkpoint or GCell Growth Checkpoint or G11 Checkpoint Checkpoint Makes the key decision of whether the cell will divide.Makes the key decision of whether the cell will divide. If the cell is healthy and large enough, proteins will If the cell is healthy and large enough, proteins will

stimulate the cell to begin the synthesis or S phase to stimulate the cell to begin the synthesis or S phase to copy the cell’s DNA.copy the cell’s DNA.

If conditions aren’t favorable, cell can stop cycle at this If conditions aren’t favorable, cell can stop cycle at this phase.phase.

Also will stop at this phase if cell needs to pass into a Also will stop at this phase if cell needs to pass into a rest period. Some cells (muscle and nerve cells) rest period. Some cells (muscle and nerve cells) remain in rest period permanently.remain in rest period permanently.

Principle Checkpoints of the Cell Principle Checkpoints of the Cell CycleCycle

2.2. DNA Synthesis Checkpoint or GDNA Synthesis Checkpoint or G22

CheckpointCheckpoint DNA replication is checked at this point by DNA replication is checked at this point by

DNA repair enzymes.DNA repair enzymes. If checkpoint is passed, will trigger mitosis If checkpoint is passed, will trigger mitosis

and cell begins many molecular processes and cell begins many molecular processes needed to proceed into mitosis.needed to proceed into mitosis.

Principle Checkpoints of the Cell Principle Checkpoints of the Cell CycleCycle

3.3. Mitosis CheckpointMitosis Checkpoint This checkpoint triggers the exit from This checkpoint triggers the exit from

mitosis.mitosis. Signals the GSignals the G11 phase (major growth period phase (major growth period

of cell cycle)of cell cycle)

When Control is Lost: CancerWhen Control is Lost: Cancer

Certain genes contain information Certain genes contain information necessary to make the proteins that necessary to make the proteins that regulate cell growth and division.regulate cell growth and division.

If one of those genes are mutated, the If one of those genes are mutated, the protein may or may not function , and protein may or may not function , and regulation of cell growth and division may regulation of cell growth and division may be disrupted.be disrupted.

When Control is Lost: CancerWhen Control is Lost: Cancer

CancerCancer – the uncontrolled growth of cells – the uncontrolled growth of cellsWhen proteins are disrupted, cancer may When proteins are disrupted, cancer may

occur.occur.Essentially a cell division disorderEssentially a cell division disorderCells do not respond to the body’s normal Cells do not respond to the body’s normal

control mechanismscontrol mechanisms

When Control is Lost: CancerWhen Control is Lost: Cancer

Some mutations cause over-production of Some mutations cause over-production of growth-promoting molecules, speeding up growth-promoting molecules, speeding up cell cyclecell cycle

Other mutations inactivate the proteins Other mutations inactivate the proteins that slow or stop the cell cycle.that slow or stop the cell cycle.

When Control is Lost: CancerWhen Control is Lost: Cancer

Mutations may occur spontaneously, but Mutations may occur spontaneously, but many occur due to environmental many occur due to environmental influences.influences.

Many causes of cancer linked to lifestyleMany causes of cancer linked to lifestyle TobaccoTobacco UV radiationUV radiation VirusesViruses Diet?Diet?

Section 6-2 SummarySection 6-2 Summary

There are 5 phases of the cell cycle: G1 phase, There are 5 phases of the cell cycle: G1 phase, S phase, G2 phase, Mitosis, and Cytokinesis.S phase, G2 phase, Mitosis, and Cytokinesis.

There are three checkpoints to determine the There are three checkpoints to determine the phase the cell will enter. If the cell does not phase the cell will enter. If the cell does not pass the checkpoint, it does not proceed into the pass the checkpoint, it does not proceed into the next phase.next phase.

Cancer is uncontrolled cell growth caused by Cancer is uncontrolled cell growth caused by mutations of the genes that control the cell cycle.mutations of the genes that control the cell cycle.

Section 6-2 HomeworkSection 6-2 Homework

Review Questions Review Questions

page 127 (1-4)page 127 (1-4)

STUDY FOR CHAPTER 6 STUDY FOR CHAPTER 6 VOCABULARY TEST!!!!VOCABULARY TEST!!!!