ENZYMES

An enzyme acts as a catalyst to a chemical reaction by

• lowering the activation energy needed to get the reaction started.
• making one of the substrates needed for the reaction.
• regulating the temperature at which the reaction takes place.
• regulating the pH at which the reaction takes place.

How do enzymes control chemical reactions in the body?

• Enzymes speed up chemical reactions.
• Enzymes slow down chemical reactions.
• Enzymes increase the activation energy of a reaction.
• Enzymes inhibit the catalysts of a reaction.

The graph shows the effect of temperature on enzyme action. What characteristic do enzymes E₁, E₂, and E₃ share?

• Their activity increases between 20°C and 30°C.
• Their activity is greatest between 5°C and 10°C.
• Their activity is at a low level between 15°C and 25°C.
• Their activity is at a high level between 30°C and 40°C.

Enzymes are proteins that are found in cells. What is their role?

• They speed up chemical reactions in cells.
• They lower the activation energy needed for some reactions.
• They regulate the absorption of energy in chemical reactions.
• All the other answers are correct.

Enzymes provide a site where reactants called substrates can be brought together in an enzyme-catalyzed reaction. The site is called the

• enzyme substrate complex.
• reaction site.
• active site.
• lock and key.

A change in pH can change the shape of a protein. How might a change in pH affect the function of an enzyme? 

• A new enzyme may be required to speed up the reaction.
• The enzyme may no longer be able to function for the substrate as a catalyst.
• The enzyme and substrate may no longer fit together so the enzyme cannot speed up the reaction.
• All the other answers are correct.

The structure of biomolecules is closely related to the functions they perform in living cells. Which statement below best illustrates this concept?

• Lipids may be saturated or unsaturated.
• Carbohydrates such as starch are long chains of sugar monomers.
• The active site of a protein enzyme precisely fits the shape of its substrate molecules.
• Proteins may be made up of chains that are folded or coiled.

The graph shows how enzymes affect reactions in cells. Which statement best summarizes the information shown in the graph?

• Enzymes increase the energy of the reactants.
• Enzymes decrease the energy level of the products.
• Enzyme decrease the activation energy of the reaction.
• Enzymes reverse the direction of the reaction.

A lock and key is sometimes used as a model to promote understanding of enzymes. Which characteristic of enzymes or their action is best illustrated by this model?

• The sensitivity of enzymes to changes in pH
• The change in activation energy the enzymes cause
• The specificity of fit between an enzyme and a substrate
• The increase in reaction rate due to the action of the enzyme

How do enzymes work?

• Slow down chemical reactions
• Prevent chemical reactions from working
• increase the activation energy
• speed up the chemical reaction