Chapter 8

Imagine an exergonic reaction with the given set of energy values. Match the energy values to the correct state or quantity.

1) Transition state (initial state + EA) :750 kJ/mol 2) Reactants (initial state) :600 kJ/mol 3) Activation energy (EA) :150 kJ/mol 4) Products (final state) :200 kJ/mol 5) ΔG (final state minus initial state) :-400 kJ/mol

As ATP begins to build up in a cell, metabolism slows down. How does this happen?

ATP acts as an allosteric inhibitor to many of the enzymes involved in metabolism, thus slowing their function.

Cells use ATP constantly, but ATP is considered a renewable resource. What process makes this possible?

ATP can be regenerated by the addition of a phosphate group to ADP.

A new drug inhibits the action of a specific enzyme by binding to it. The drug is unaffected by changes in the concentration of the substrate. What is this drug?

Allosteric regulator Noncompetitive inhibitor

Which of the following correctly states the relationship between anabolic and catabolic pathways?

Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.

At low temperatures, a particular enzyme catalyzes a reaction, but at a slow rate. At high temperatures, the enzyme is completely inactive. What statement best explains the difference in how temperature affects the function of this enzyme?

At low temperatures, there is not enough free energy for the enzyme to function at a high rate, and at high temperatures, the enzyme is denatured, leaving it nonfunctional.

Which of the following statements correctly describes cofactors and coenzymes?

Both are nonprotein enzyme helpers; but most cofactors are metal ions, and coenzymes are organic molecules that are a specific type of cofactor.

Match the term to its definition or example.

Catalyst ~Selectively increases the rate of a reaction Catabolic pathway ~Releases energy by breaking down complex molecules Anabolic pathway ~A protein is synthesized from amino acids. Spontaneous pathway ~An iron railing rusts.

Which of the following statements is correct regarding competitive and noncompetitive enzyme inhibitors?

Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to an enzyme away from the active site.

Regarding the ATP cycle, which are correct?

Energy coupling is the use of an exergonic process to drive an endergonic one. If the ΔG of an endergonic reaction is less than the amount of energy released by ATP hydrolysis, then the two reactions can be coupled. The phosphorylated intermediate is more reactive than the original unphosphorylated molecule.

Regarding enzymes, which are correct?

Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output. The active site lowers the EA of the reaction. Enzymes may act on more than one substrate. The enzyme changes shape during catalysis. After catalysis, the enzyme returns to its original form. When an enzyme binds to its substrate molecule(s), a temporary enzyme-substrate complex is formed.

Which of the following statements about enzymes is true?

Enzymes speed up the rate of the reaction without changing the ΔG for the reaction.go to explanation

The primary manner in which cells manage their energy resources in order to do work is called energy coupling. Which of the following statements accurately defines energy coupling?

Exergonic reactions drive endergonic reactions.

Which of the following reactions would be endergonic?

Glucose + fructose → sucrose

Regarding metabolic reactions, which are correct?

Higher G systems tend to change in such a way that they become lower G. Exergonic reactions are spontaneous. For exergonic reactions, ΔG is negative. The ΔG of an endergonic reaction is positive. The magnitude of ΔG for an exergonic reaction represents the maximum amount of work the reaction can perform.

Which of the following is true regarding metabolic pathways?

Metabolic pathways consist of a series of reactions, each catalyzed by a different enzyme.

Which of these statements about enzyme inhibitors is true?

The action of competitive inhibitors may be reversible or irreversible

Which of the following is changed by the presence of an enzyme in a reaction

The activation energy

Which of the following statements about the active site of an enzyme is correct?

The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.

Which of the following is an example of the second law of thermodynamics as it applies to biological reactions?

The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water.

Which of the following statements is correct regarding ATP?

The energy in an ATP molecule is released through hydrolysis of one of the phosphate groups.

What best characterizes the role of ATP in cellular metabolism?

The free energy released by ATP hydrolysis that may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

The graph shows the rate of reaction of two digestive enzymes over a range of pH values. Match the adjustment to pH with the corresponding effect.

The rate of reaction of trypsin will decrease. ~ Decrease pH from 8 to 5 The rate of reaction of pepsin will increase. ~ Decrease pH from 3 to 2.4 Neither enzyme will function. ~ Increase pH from 7.1 to 9.2 The rate of reaction of trypsin will increase. ~ Increase pH from 6 to 7 The rate of reaction of pepsin will decrease. ~ Increase pH from 1.8 to 3

The illustration shows two versions of the same reaction, one with an enzyme and one without. Which are correct?

The red curve [2] shows the reaction with the enzyme. The presence of the enzyme lowers EA. The red arrow [4] shows EA in the presence of the enzyme The yellow arrow [5] shows that the enzyme has no effect on ΔG.

ATP allosterically inhibits enzymes in ATP-producing pathways. The result of this is called __________.

feedback inhibition

Enzyme activity is affected by pH because __________.

high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

An exergonic (spontaneous) reaction is a chemical reaction that __________.

releases energy when proceeding in the forward direction

An exergonic reaction __________ free energy, and an endergonic reaction __________ free energy.

releases; absorbs

In general, the hydrolysis of ATP drives cellular work by __________.

releasing free energy that can be coupled to other reactions

How does ATP drive mechanical work inside a cell?

By binding to motor proteins

How does ATP drive transport work inside a cell?

By phosphorylating a transport protein

Vioxx and other prescription nonsteroidal anti-inflammatory drugs (NSAIDs) are potent inhibitors of the cyclooxygenase-2 (COX-2) enzyme. High substrate concentrations reduce the efficacy of these drugs. What is Vioxx?

Competitive inhibitor

Which of the following states the relevance of the first law of thermodynamics to biology?

Energy can be freely transformed among different forms as long as the total energy is conserved

Which of the following statements is correct regarding kinetic and potential energy?

Kinetic energy is associated with the relative motion of objects, and potential energy is the energy that matter possesses because of its location or structure.