1. How do you think the body repairs an injury, such as a cut on a finger?

1. How do you think the body repairs an injury, such as a cut on a finger?

The cut is repaired by the production of new cells through cell division.

2. How long do you think this repair process continues?

Cell division continues until the cut is repaired.

3. What do you think causes the cells to stop the repair process?

Students will likely say that when the cut is filled in, there is no room for more cells to grow.

Knowing When to Stop

Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new.

REGULATING the

CELL CYCLE

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Control of Cell Division

Section 10-3

Cells grow until they touch other cells

If center cells are removed,cells near the space will start to grow again.

SHOWS: Cell division genes can be turned on and off

CELL DIVISION GENES

EXAMPLE: Cell division genes can be ________ in case of injury.

Cells near injury are stimulated to divideto heal and replacedamaged/missing cells and shut off when the repair has been made.

turned on

CELL DIVISION GENES

Some cells divide frequently(some human skin cells divide once/hour)

Some cells divide occasionally (liver cells divide about once/year)

Some cells don’t divide once they form (nerve cells)

In early 1980’s scientists discovered aprotein in dividing cells that caused a ______________to form in

_______________ cells

CELL CYCLE REGULATORS

Mitotic spindleNON-dividing

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Levels of this protein rose and fell withthe cell cycle so it was named__________ because it seemed tocontrol the cell cycle.

A whole family ofCYCLINS have since beendiscovered that regulate the_____________________in EUKARYOTIC CELLS

CELL CYCLE REGULATORS

CYCLIN

TIMING of CELL CYCLE

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______________ REGULATORSProteins that respond to events insidethe cell.

Allow cell cycle to proceed only if certain processes have happened

EX: Cell can’t enter mitosis until all thechromosomes have been copied

OTHER REGULATORSINTERNAL

______________ REGULATORSProteins that respond to events outsidethe cell.

Signals tell cell to speed up or slow down the cell cycle

EX: Growth factors stimulate cells to divideEspecially important duringwound healing and embryo development

OTHER REGULATORSEXTERNAL

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Molecules on the surface of neighboringcells act as signals to slow down or stop thecell’s cycle.

These signals preventexcessive growth andkeep tissues from disrupting each other.

EXTERNAL REGULATORS

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Cancer cells have lost control of their cell division

genes

CHO (Chinese Hamster Ovary) cells in culture

SEM Image by: Riedell

Cancer cells don’t stopwhen they touch nearbycells. . . they just keep growing!

That’s what makesa tumor.

NO CONTACT INHIBITION

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Cancer cells• Don’t stop dividing• Like a “car with no brakes”• Can spread to new places

(METASTASIS)

• ______________ are substances that can damage DNA and cause cancer

Ex: Cigarette smoke (OR CHEW), Radiation, chemicals in environment, even viruses,

Carcinogens

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Cancer cellsCancer is complicated and can have

many causes, but all cancers have one thing in common …

They have lost control over their _____________.

Many cancers cells have a damaged or defective

gene called _____, so they can’t respond tonormal cell signals to control their growth.

CELL CYCLE

p53

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