Chapter 8 Mastering Biology
Living organisms increase in complexity as they grow, resulting in a decrease in the entropy of an organism. How does this relate to the second law of thermodynamics? As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth. Life obeys the second law of thermodynamics because the decrease in entropy as the organism grows is exactly balanced by an increase in the entropy of the universe. Living organisms are able to transform energy into entropy. Living organisms do not follow the laws of thermodynamics. Living organisms do not obey the second law of thermodynamics, which states that entropy must increase with time.
As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.
When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell? -It is secreted as waste. -It may be used to form a phosphorylated intermediate. -It enters the nucleus and affects gene expression. -It is used only to regenerate more ATP. -It is added to water and excreted as a liquid.
It may be used to form a phosphorylated intermediate.
Which of these is exhibiting kinetic energy?
a space station orbiting Earth
A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. What is substance X? an allosteric inhibitor a substrate the product a coenzyme an intermediate
a substrate
The following question is based on the reaction A + B ↔ C + D shown in the figure. Which of the following terms best describes the forward reaction in the figure?
exergonic G<0
What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?
hydrolysis
Which temperature and pH profile curves on the graphs were most likely generated from analysis of an enzyme from a human stomach where conditions are strongly acid?
1 and 4 because 4 is acidic and the middle of 1 is at 98.6 degrees F and 36.6 C
You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again? Add more inhibitor to speed up the reaction. Add more substrate; it will outcompete the inhibitor and increase the reaction rate. Increase the temperature. Increase the pH.
Add more substrate; it will outcompete the inhibitor and increase the reaction rate.
How does an enzyme increase the rate of the chemical reaction it catalyzes? An enzyme's active site binds only the reactants, and not the products of a reaction, pushing the equilibrium for the reaction far to the right. An enzyme reduces the free energy of activation (EA) of the reaction it catalyzes. An enzyme reduces the free-energy change (ΔG) of the reaction it catalyzes.
An enzyme reduces the free energy of activation (EA) of the reaction it catalyzes.
Which statement about the binding of enzymes and substrates is correct? When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape. Substrate molecules fit into the active site of an enzyme like a key fits into a lock. Substrate molecules bind to the active site of the enzyme only by weak bonds, such as hydrogen bonds or hydrophobic attraction.
When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape.
A _______________ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate.
competitive
As a result of its involvement in a reaction, an enzyme _____. loses energy permanently alters its shape. is unchanged is used up loses a phosphate group
is unchanged
For living organisms, which of the following is an important consequence of the first law of thermodynamics? The energy content of an organism is constant. The entropy of an organism decreases with time as the organism grows in complexity. Organisms grow by converting energy into organic matter. The organism ultimately must obtain all of the necessary energy for life from its environment. Life does not obey the first law of thermodynamics.
The organism ultimately must obtain all of the necessary energy for life from its environment.
Which of the following is true for all exergonic reactions? -The reaction proceeds with a net release of free energy. - A net input of energy from the surroundings is required for the reactions to proceed. -The reactions are rapid. - The products have more total energy than the reactants. - The reaction goes only in a forward direction: all reactants will be converted to products, but no products will be converted to reactants.
The reaction proceeds with a net release of free energy.
The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____. an endergonic pathway a pathway that converts organic matter into energy a pathway that occurs in animal cells but not plant cells a catabolic pathway a pathway in which the entropy of the system decreases
a catabolic pathway
Chemical equilibrium is relatively rare in living cells. Which of the following could be an example of a reaction at chemical equilibrium in a cell? -a chemical reaction in which both the reactants and products are not being produced or used in any active metabolic pathway at that time in the cell - an endergonic reaction in an active metabolic pathway where the energy for that reaction is supplied only by heat from the environment - no possibility of having chemical equilibrium in any living cell - a reaction in which the free energy at equilibrium is higher than the energy content at any point away from equilibrium -a chemical reaction in which the entropy change in the reaction is just balanced by an opposite entropy change in the cell's surroundings
a chemical reaction in which both the reactants and products are not being produced or used in any active metabolic pathway at that time in the cell
Which of the following is an example of cooperatively? -the binding of an end product of a metabolic pathway to the first enzyme that acts in the pathway -the effect of increasing temperature on the rate of an enzymatic reaction -one enzyme in a metabolic pathway passing its product to act as a substrate for the next enzyme in the pathway -binding of an ATP molecule along with one of the substrate molecules in an active site -a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three
a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three
Which of the following types of reactions would decrease the entropy within a cell? digestion catabolic reactions respiration anabolic reactions hydrolysis
anabolic reactions
What is the correct label for "A"?
energy of activation
how do cells use the ATP cycle shown above?
to recycle ADP and Phosphate
The mathematical expression for the change in free energy of a system is ΔG =ΔH - TΔS. Which of the following is (are) correct? T is the temperature in degrees Celsius. ΔH is the change in entropy, the energy available to do work. ΔG is the change in free energy. ΔS is the change in enthalpy, a measure of randomness.
ΔG is the change in free energy.
Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions? α -phosphate (the phosphate closest to ribose) β-phosphate (the middle phosphate) γ-phosphate (the terminal phosphate) adenine group ribose sugar
γ-phosphate (the terminal phosphate)
During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the G for the new reaction? +40 kcal/mol 0 kcal/mol +20 kcal/mol -20 kcal/mol -40 kcal/mol
-20 kcal/mol
Which of the following statements about equilibrium of chemical reactions is correct? - A reaction that is at equilibrium is not capable of doing any work. - The equilibrium point is where the system has the highest free energy - Reactions can only go in the direction toward equilibrium. - The equilibrium point of a reaction represents the least stable configuration for that reaction. - Most reactions in a living cell are close to equilibrium.
A reaction that is at equilibrium is not capable of doing any work. *at equilibrium, delta G is zero
Which of the following is true of metabolism in its entirety in all organisms? Metabolism depends on a constant supply of energy from food. Metabolism manages the increase of entropy in an organism. Metabolism uses all of an organism's resources. Metabolism consists of all the energy transformation reactions in an organism. Metabolism depends on an organism's adequate hydration.
Metabolism consists of all the energy transformation reactions in an organism.
When 10,000 molecules of ATP are hydrolyzed to ADP and i in a test tube, about half as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation? -The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes. - Cells are open systems, but a test tube is an isolated system. -Cells are less efficient at heat production than nonliving systems. -Reactant and product concentrations in the test tube are different from those in the cell. -The hydrolysis of ATP in a cell produces different chemical products than does the reaction in a test tube.
Reactant and product concentrations in the test tube are different from those in the cell.
In a biological reaction, succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, a substance that resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the amount of succinate molecules to those of malonic acid reduces the inhibitory effect if malonic acid. Select the correct identification of the molecules described in the reaction. -Succinate dehydrogenase is the enzyme, and fumarate is the substrate in the reaction. -Fumarate is the product, and malonic acid is a noncompetitive inhibitor in the reaction. -Succinate is the substrate, and fumarate is the product in the reaction. -Succinate dehydrogenase is the enzyme, and malonic acid is the substrate in the reaction.
Succinate is the substrate, and fumarate is the product in the reaction.
Which of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes? -The binding of two substrates in the active site provides the correct orientation for them to react to form a product. -Binding of the substrate to the active site can stretch bonds in the substrate that need to be broken. -The active site can provide heat from the environment that raises the energy content of the substrate. -The enzyme binds a cofactor that interacts with the substrate to facilitate the reaction. - The active site of the enzyme can provide a microenvironment with a different pH that facilitates the reaction.
The active site can provide heat from the environment that raises the energy content of the substrate.
Which of the following statements about ATP (adenosine triphosphate) is correct? The hydrolysis of ATP is an endergonic process. Almost all of the free energy released on the hydrolysis of ATP is released as heat. The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways. The hydrolysis of ATP can supply energy needed for catabolic pathways. The energy release on hydrolysis of ATP is the result of breaking a high-energy bond.
The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways.
Which of the following statements about the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O) is correct? -The free energy lost in this combustion is less than the energy that appears as heat. - The reverse reaction, making glucose from water and carbon dioxide, must be an exergonic reaction. - The entropy of the universe decreases as the result of this reaction. -The entropy of the products is greater than the entropy of the reactants. - This is the process of cellular respiration, an anabolic pathway that releases free energy.
The entropy of the products is greater than the entropy of the reactants.
The competitive inhibitor competes with the substrate for the__________________ on the enzyme.
active site
highest energy form of Adenosine?
adenosine triphosphate=ATP
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? allosteric inhibition saturation of the enzyme activity competitive inhibition insufficient cofactors denaturation of the enzyme
competitive inhibition
When the noncompetitive inhibitor is bonded to the enzyme , the shape of the ___________ is distorted.
enzyme
Which of these are by-products of cellular respiration? - heat, carbon dioxide, and water -carbon dioxide and water -glucose, carbon dioxide, and water - ATP and carbon dioxide - ATP, carbon dioxide, and water
heat, carbon dioxide and water
A _____________ inhibitor binds to a site on the enzyme that is not the active site.
noncompetitive
Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown?
p4 binds E1 and deactivates it
chemical energy is a form of ________ energy
potential energy
In general, enzymes are what kinds of molecules?
proteins
Enzymes work by _____. increasing the potential energy difference between reactant and product decreasing the potential energy difference between reactant and product adding energy to a reaction reducing EA adding a phosphate group to a reactant
reducing EA
Enzyme inhibitors disrupt normal interactions between an enzyme and its .________________
substrate
What name is given to the reactants in an enzymatically catalyzed reaction?
substrate
A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because - the starch solution has less free energy than the sugar solution. - starch hydrolysis is nonspontaneous. - starch cannot be hydrolyzed in the presence of so much water. - the hydrolysis of starch to sugar is endergonic. - the activation energy barrier for this reaction cannot easily be surmounted at room temperature.
the activation energy barrier for this reaction cannot easily be surmounted at room temperature.
Protein kinases are enzymes that catalyze phosphorylation of target proteins at specific sites, whereas protein phosphatases catalyze removal of phosphate(s) from phosphorylated proteins. Phosphorylation and dephosphorylation can function as an on-off switch for a protein's activity, most likely through -the excision of one or more peptides. - the change in a protein's charge leading to a conformational change. -a change in the optimal pH at which a reaction will occur. -the change in a protein's charge leading to cleavage. -a change in the optimal temperature at which a reaction will occur.
the change in a protein's charge leading to a conformational change.
Which of the following statements is a logical consequence of the second law of thermodynamics? Every chemical reaction must increase the total entropy of the universe. Every energy transfer requires activation energy from the environment. If there is an increase in the energy of a system, there must be a corresponding decrease in the energy of the rest of the universe. Energy can be transferred or transformed, but it cannot be created or destroyed. If the entropy of a system increases, there must be a corresponding decrease in the entropy of the universe.
Every chemical reaction must increase the total entropy of the universe.
For the hydrolysis of ATP to ADP + i, the free energy change is -7.3 kcal/mol under standard conditions (1 M concentration of both reactants and products). In the cellular environment, however, the free energy change is about -13 kcal/mol. What can we conclude about the free energy change for the formation of ATP from ADP and i under cellular conditions? It is less than +7.3 kcal/mol. It is greater than +13 kcal/mol. It is about +13 kcal/mol. It is +7.3 kcal/mol. The information given is insufficient to deduce the free energy change.
It is greater than +13 kcal/mol.
Select the correct statement about chemical energy, a term used by biologists to refer to potential energy available for release in a chemical reaction. -A photosynthetic cell within a plant leaf produces chemical energy, stored within glucose molecules. -Light energy is converted to chemical energy during photosynthesis. -When a glucose molecule is catabolized to CO2 and H2O, chemical energy is lost.
Light energy is converted to chemical energy during photosynthesis.
You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme? -Removing the irreversible inhibitor should get the reaction working again. - The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity. -Adding more substrate will increase the rate of reaction. -Adding more inhibitor should get the reaction up to speed again.
The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.
Which of the following statements about feedback regulation of a metabolic pathway is correct? -Accumulation of the product of the pathway increases further formation of that product. -The compound that regulates the pathway acts as a competitive inhibitor or a positive allosteric regulator. -The enzyme that is regulated by feedback inhibition is usually the last enzyme in the metabolic pathway. -The final product of a metabolic pathway is usually the compound that regulates the pathway. -The products of the pathway become the reactants for a different reaction, and thus products are unable to accumulate.
The final product of a metabolic pathway is usually the compound that regulates the pathway.
What is the free energy change (ΔG) of the hydrolysis of ATP to ADP?
The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi may vary considerably with variations in pH, temperature, atmospheric pressure, and concentrations of reactants and products.
In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP? - cellular respiration -redox - anabolism - digestion - potentiation
cellular respiration
When you have a severe fever, what grave consequence may occur if the fever is not controlled? - binding of your enzymes to inappropriate substrates - destruction of your enzymes' primary structure - change in the tertiary structure of your enzymes - removal of the amino acids in active sites of your enzymes - removal of amine groups from your proteins
change in the tertiary structure of your enzymes
Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n) - coenzyme derived from a vitamin. -allosteric activator of the enzyme. -cofactor necessary for enzyme activity. -noncompetitive inhibitor of the enzyme. -competitive inhibitor of the enzyme.
cofactor necessary for enzyme activity.
A chemical reaction that has a positive ΔG is best described as exergonic. entropic spontaneous. endergonic. enthalpic.
endergonic
"Conservation of energy" refers to the fact that _____. -the net amount of disorder is always increasing - if you conserve energy you will not be as tired - no chemical reaction is 100 percent efficient - energy cannot be created or destroyed but can be converted from one form to another - the entropy of the universe is always increasing
energy cannot be created or destroyed but can be converted from one form to another
Usually, a(n)_____________________ inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity.
irreversible
An enzyme _____. can bind to nearly any molecule is a inorganic catalyst increases the EA of a reaction is an organic catalyst is a source of energy for endergonic reactions
is an organic catalyst
Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity? -hydrophobic interactions -connecting enzymes into large aggregates -localization of enzymes into specific organelles or membranes -cessation of cellular protein synthesis - exporting enzymes out of the cell
localization of enzymes into specific organelles or membranes
Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy? -the covalent bonds of a sugar molecule: potential energy - the motion of individual molecules: potential energy -the energy related to the height of a bird above the ground: kinetic energy - the energy associated with a gradient of ions across a membrane: kinetic energy - the heat released from a living organism: potential energy
the covalent bonds of a sugar molecule: potential energy the bonds in covalent bonds create energy from the relative positions that form the bonds
Which of the following statements about the role of ATP in cell metabolism is true? - The energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule. -The free energy released by ATP hydrolysis has a much more negative ΔG value than the hydrolysis of phosphate groups from other phosphorylated molecules. -The phosphate bonds of ATP are unusually strong bonds.
the energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule.