Ch. 20 Enzymes and Vitamins

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In the lock-and-key model of enzyme action, the enzyme active site is thought of as

a rigid, nonflexible shape that fits the substrate exactly

When a substance bonds to an enzyme for reaction, its place of binding is the

active site

In the induced-fit model of enzyme action, the enzyme active site

adjusts shape to adapt to the shape of the substrate

The purpose of the many chemical reactions in our bodies is to

all of the above.

A noncompetitive inhibitor

alters the three-dimensional structure of the enzyme.

A competitive inhibitor is one that

binds to the active site in place of the substrate

The presence of enzymes to catalyze bioreactions in our bodies allows

bioreactions to take place under mild conditions

The general function of an enzyme in the body is to

catalyze chemical reactions

The active site of an enzyme

catalyzes the reaction

When a cofactor is a small organic molecule, it is known as a/an

coenzyme

The water-soluble B and C vitamins supply

coenzymes required by some enzymes.

Metal ions such as Zn²+ and Fe³+ are often needed by enzymes as

cofactors

The function of the enzyme-substrate complex is to provide an alternative reaction pathway that

decreases the activation energy for the reaction

The formation of an enzyme-substrate complex is the __________ step in enzyme action.

first

Most enzymes are

globular proteins

Hexokinase catalyzes only the addition of phosphate to any hexose sugar. This type of activity is called

group specificity

To what main class of enzymes does the enzyme that catalyzes the conversion of lactose to galactose and glucose belong?

hydrolase

To what main class of enzymes does the enzyme that catalyzes the following reaction belong? ser-ala → ser + ala

hydrolase

In an enzyme-substrate reaction, when excess substrate is present, increasing the concentration of the enzyme wil

increase the amount of reaction occuring

Penicillin functions as an antibiotic by

inhibiting the enzymes for cell wall formation in bacteria

Substances that react under the influence of an enzyme are usually held to the enzyme by

side chains of amino acids in the enzyme protein.

In any reaction catalyzed by an enzyme, the reacting molecule is called the

substrate

The B vitamins are examples of

water-soluble vitamins

Compared to an uncatalyzed reaction, an enzyme-catalyzed reaction

occurs at a faster rate

The optimum temperature for sucrase activity is 37 °C. The hydrolysis of sucrose is slowest at which temperature in the choices below?

0°C

Most enzymes are deactivated permanently above a temperature of about

50°C

"Physiological pH", the pH for optimum activity for most enzymes, is a pH equal to

7.4

Which of the following is NOT true for a competitive inhibitor?

It binds to the enzyme at a site remote from the active site.

Urea is converted to ammonia and carbon dioxide by the action of urease. What will be the effect on the rate if the temperature of the reaction is lowered from 37 °C (the optimum temperature) to 27 °C?

The rate will slow down

Which of the following is NOT a step in the enzyme-catalyzed conversion of a substrate to product?

The substrate changes its shape so it can bind at the active site.

A noncompetitive inhibitor has a structure that

does not resemble the substrate structure

Coenzymes such as water-soluble vitamins are needed in only small amounts because

each vitamin molecule can be reused many times as a cofactor

A compound that binds to the surface of an enzyme, and changes its shape so that a substrate cannot enter the active site, is called a/an

noncompetitive inhibitor

The hydrolysis of ester bonds in triglycerides is catalyzed by a/an

lipase

Small molecules that make up the repeat unit in polymers are called

monomers

To what main class of enzymes does the enzyme that catalyzes the following reaction belong?

oxidoreductase

"Physiological conditions" for reactions within the body are approximately

pH 7 and 37°C


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