Notes 2-4

Chemical Reactions and Enzymes

•Chemical Reaction:

−A process that changes one set of chemicals into another set of chemicals

•Reactants:

−Elements entered into the reaction

•Products:

−Elements or Compounds produced by the reaction

Always involves breaking old bonds and forming new ones!

REACTANTS PRODUCTS

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Enzymes affect the reactions in living cells by changing the

A. products of the reaction.

B. speed of the reaction.

C. temperature of the reaction.

D. pH of the reaction.

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Energy in Reactions:

•Energy is either released or absorbed in chemical reactions…Why?−Because bonds are formed or broken!

•The energy needed to get a reaction started is called…Activation Energy

•Chemical reactions inside living things have 2 main problems!

-Chemical reactions in living things are too slow

-Some have a high activation energy

-Solution: catalysts

Enzymes

•Catalyst:

−A substance that speeds up the rate of chemical reactions by lowering the activation energy required for the reaction to occur.

•Enzymes:

−Proteins that act as biological catalysts.

−Enzymes speed up chemical reactionswithin the cell.

Enzymes

Detailed Animation

http://telstar.ote.cmu.edu/biology/animation/SerineProtease/SerineProtease_bc.html

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What is the term used to describe the

energy needed to get a reaction started?

A. adhesion energy

B. activation energy

C. cohesion energy

D. chemical energy

Answer Now 15

Enzyme-Substrate Complex: How an Enzyme Works

•Substrates (reactants) bind to an enzyme’s active site

−Active site lowers the activation energy = reaction happens faster

Active site?

Enzymes-Substrate Complex

•When the substrate binds to the enzyme at the active site the catalytic action of the enzyme converts the substrate to the product

•Enzymes usually end in “-ase”

Copy the equation below:

SUBSTRATE(S) PRODUCT(S)

enzyme

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What is the definition of an active site?

A. The final product of an enzyme catalyzed reaction

B. The spot on the substrate where the enzyme binds to

C. The spot on the enzyme where the substrate binds to

D. None of the above

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An enzyme’s ____________ is the molecule upon which an enzyme acts.

A. active site

B. inhibitor

C. Catalyst

D. substrate

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Remember…

•Enzymes provide an active site where substrates can be brought together to react.

−Active site reduces the energy needed for a reaction

•The fit is like a lock and key

−Each enzyme (protein) has a specific shape

−Each substrate has a complementary shape

•The enzyme remains unchanged!

speed

up

slow

down

inhibit destroy

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Increasing the concentration of an enzyme’s substrate (up to a point) would ___________ the reaction.

A. speed up

B. slow down

C. inhibit

D. destroy

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Regulation of Enzyme Activity

•Enzymes can be affected by 2 Things:

−pH

−Temperature

Regulation of Enzyme Activity:Temperature

•Temperature

−A change in the optimal temperature can cause a protein to lose its shape = “denaturing”

•When an enzymes denatures, it loses its shapeand cannot function properly anymore

Regulation of Enzyme Activity:pH

•pH

−Each enzyme also has an optimal pH

−Usually pH of 6-8

−Exceptions

•Pepsin (digestive enzyme in your stomach) -pH 2

enzyme X enzyme Y

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A. enzyme X

B. enzyme Y

According to Figure 2–3, which enzyme has an optimum temperature of 40°C?

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Which of the following might be an enzyme?

A. Sucrose

B. Glucose

C. Glycogen

D. Amalase

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En

zym

es…

Enzy

mes

…

Enzy

mes

…

The

shap

e…

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Which of the following statements about enzymes is NOT true?

A. Enzymes work best at a specified pH.

B. Enzymes are lipids.

C. Enzymes are proteins.

D. The shape of an enzyme allows it to do its job.

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The speed or rate of a chemical reaction is influenced by all of the following except________.

A. the concentration of the reactants

B. the presence of catalysts or enzymes

C. the presence or absence of carbon

D. the temperature

15Answer Now

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