Concept 8.5: Regulation of enzyme activity helps control metabolism

Question 1

is the term used to describe any case in which a protein’s function at one site is affected by the binding of a regulatory molecule to a separate site

Answer 1

Allosteric regulation

Question 2

It may result in either

Answer 2

inhibition or stimulation of an enzyme’s activity.

Question 3

Most enzymes known to be allosterically regulated are constructed from two or more

Answer 3

subunits, each composed of a polypeptide chain with its own active site.

Question 4

The entire complex oscillates between two different shapes, one

Answer 4

catalytically active and the other inactive

Question 5

In the simplest kind of allosteric regulation, an activating or inhibiting regulatory molecule binds to a regulatory site (sometimes called an

Answer 5

allosteric site), often located where subunits join.

Question 6

The binding of an ___________ to a regulatory site stabilizes the shape that has functional active sites, whereas the binding of an__________ stabilizes the inactive form of the enzyme.

Answer 6

activator, inhibitor

Question 7

The subunits of an allosteric enzyme fit together in such a way that a shape change in one subunit is

Answer 7

transmitted to all others

Question 8

Through this interaction of subunits, a single activator or inhibitor molecule that binds to one regulatory site will affect the active sites of all

Answer 8

subunits.

Question 9

Fluctuating concentrations of regulators can cause a sophisticated pattern of response in the activity of

Answer 9

cellular enzymes

Question 10

ATP binds to several catabolic enzymes allosterically, lowering their affinity for substrate and thus

Answer 10

inhibiting their activity

Question 11

If ATP production lags behind its use, ADP accumulates and activates the enzymes that speed up catabolism, producing more

Answer 11

ATP

Question 12

ATP, ADP, and other related molecules also affect key enzymes in

Answer 12

anabolic pathways

Question 13

another kind of allosteric activation, a substrate molecule binding to one active site in a multisubunit enzyme triggers a shape change in all the subunits, thereby increasing catalytic activity at the other active sites called

Answer 13

cooperativity

Question 14

Cooperativity is considered allosteric regulation because, even though substrate is binding to an active site, its binding affects

Answer 14

catalysis in another active site.

Question 15

Hemoglobin is made up of

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four subunits, each with an oxygen-binding site

Question 16

The binding of an oxygen molecule to one binding site increases the

Answer 16

affinity for oxygen of the remaining binding sites

Question 17

In oxygen-deprived tissues, however, the release of each oxygen molecule decreases the

Answer 17

oxygen affinity of the other binding sites, resulting in the release of oxygen where it is most needed.

Question 18

in which a metabolic pathway is halted by the inhibitory binding of its end product to an enzyme that acts early in the pathway.

Answer 18

feedback inhibition

Question 19

Some cells use this five-step pathway to synthesize the amino acid isoleucine from threonine, which is

Answer 19

another amino acid.

Question 20

As isoleucine accumulates, it slows down its own synthesis by allosterically inhibiting the

Answer 20

enzyme for the first step of the pathway.

Question 21

feedback inhibition thereby prevents the cell from making more isoleucine than is necessary and thus

Answer 21

wasting chemical resources.

Question 22

In some cases, a team of enzymes for several steps of a metabolic pathway are assembled into a

Answer 22

multienzyme complex

Question 23

Some enzymes and enzyme complexes have fixed locations within the cell and act as .

Answer 23

structural components of particular membranes

Question 24

Others are in solution within particular membrane-enclosed eukaryotic organelles, each with its own

Answer 24

internal chemical environment.