PRACTICE QUIZ CHAP. 8

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Which of the following correctly states the relationship between anabolic and catabolic pathways?
1) Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways.
2) Energy derived from catabolic pathways is used to drive the breakdown of organic molecules in anabolic pathways.
3) Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.
4) Catabolic pathways produce usable cellular energy by synthesizing more complex organic molecules.
5) The flow of energy between catabolic and anabolic pathways is reversible.

3

Which of the following situations represent(s) a transformation of one type of energy to another?
1) the burning of gasoline in a car engine to move a car
2) the production of sugar by photosynthesis
3) the production of electrical power by damming a river
4) playing music by putting new batteries in your CD player
5) all of the above

5

Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description?
1) The metabolism of an organism is isolated from its surroundings.
2) Because energy must be conserved, organisms constantly recycle energy and thus need no input of energy.
3) Organisms acquire energy from their surroundings.
4) Heat produced by the organism is conserved in the organism and not lost to the environment.
5) all of the above

3

Consider the growth of a farmer's crop over a season. Which of the following correctly states a limitation imposed by the first or second law of thermodynamics?
1) The entropy of the universe must decrease to account for the increased entropy associated with plant growth.
2) The process of photosynthesis produces energy that the plant uses to grow.
3) To obey the first law, the crops must represent an open system.
4) Growth of the crops must occur spontaneously.
5) all of the above

3

Which of the following states the relevance of the first law of thermodynamics to biology?
1) The total energy taken in by an organism must be greater than the total energy stored or released by the organism.
2) Energy can be freely transformed among different forms as long as the total energy is conserved.
3) Photosynthetic organisms produce energy in sugars from sunlight.
4) All organisms must produce some heat as a result of the processes of life.
5) Living organisms must increase the entropy of their surroundings.

2

Which is the most abundant form of energy in a cell?
1) chemical and electrical gradients
2) mechanical energy
3) heat
4) kinetic energy
5) chemical energy

5

Which of the following is an example of the second law of thermodynamics as it applies to biological reactions?
1) The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water.
2) All types of cellular respiration produce ATP.
3) Cellular respiration releases some energy as heat.
4) The first and second choices are correct.
5) The first, second, and third choices are correct.

1

According to the second law of thermodynamics, which of the following is true?
1) Energy conversions increase the order in the universe.
2) The total amount of energy in the universe is constant.
3) The decrease in entropy associated with life must be compensated for by an increase in entropy in the environment that life occurs in.
4) The entropy of the universe is constantly decreasing.
5) All reactions produce some heat.

3

If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously?
1) The entropy of the organism's environment must also be decreasing.
2) Heat is being used by the organism as a source of energy.
3) The first law of thermodynamics is being violated.
4) Energy input into the organism must be occurring to drive the decrease in entropy.
5) In this situation, the second law of thermodynamics must not apply.

4

Which one of the following has the most free energy per molecule?
1) a sugar molecule
2) an amino acid molecule
3) a starch molecule
4) a fatty acid molecule
5) a cholesterol molecule

3

Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous?
1) ΔG
2) ΔH
3) ΔS
4) TΔS
5) All of these values reveal the direction in which a reaction will go.

1

If, during a process, the system becomes more ordered, then _____.
1) ΔG is negative
2) ΔG is positive
3) ΔH is negative
4) ΔH is positive
5) ΔS is negative

5

When one molecule is broken down into six component molecules, which one of the following will always be true?
1) An input of free energy is needed.
2) ΔG is positive.
3) ΔH is negative.
4) ΔS is positive.
5) ΔS is negative.

4

From the equation ΔG = ΔH - TΔS it is clear that _____.
1) a decrease in the system's total energy will increase the probability of spontaneous change
2) increasing the entropy of a system will increase the probability of spontaneous change
3) increasing the temperature of a system will increase the probability of spontaneous change
4) The first and second choices are correct.
5) The first three choices are correct.

5

What must be true if the reaction AB + CD → AC + BD occurs spontaneously?
1) The ΔH of the reaction must be negative.
2) The ΔS of the reaction must be positive.
3) The reaction must be endergonic.
4) The difference between ΔH and TΔS must be negative.
5) all of the above

4

An exergonic (spontaneous) reaction is a chemical reaction that _____.
1) occurs only when an enzyme or other catalyst is present
2) cannot occur outside of a living cell
3) releases energy when proceeding in the forward direction
4) is common in anabolic pathways
5) leads to a decrease in the entropy of the universe

3

Which of the following reactions would be endergonic?
1) HCl → H+ + Cl-
2) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
3) ATP → ADP + Pi
4) glucose + fructose → sucrose
5) all of the above

4

Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tend to keep these pathways away from equilibrium?
1) the continuous removal of the products of a pathway to be used in other reactions
2) an input of free energy from outside the pathway
3) an input of heat from the environment
4) The first and second choices are correct.
5) The first, second, and third choices are correct.

4

Which of the following is an example of the cellular work accomplished with the free energy derived from the hydrolysis of ATP?
1) mechanical work, such as the beating of cilia
2) transport work, such as the active transport of an ion into a cell
3) chemical work, such as the synthesis of new protein
4) all of the above
5) none of the above

5

In general, the hydrolysis of ATP drives cellular work by _____.
1) changing to ADP and phosphate
2) releasing free energy that can be coupled to other reactions
3) releasing heat
4) acting as a catalyst
5) lowering the free energy of the reaction

2

Which of the following statements correctly describes some aspect of ATP hydrolysis being used to drive the active transport of an ion into the cell against the ion's concentration gradient?
1) ATP is acting as a transport protein to facilitate the movement of the ion across the plasma membrane.
2) The hydrolysis of ATP endergonic, and the active transport exergonic.
3) Neither ATP hydrolysis nor active transport is spontaneous.
4) This is an example of energy coupling.
5) Both ATP hydrolysis and active transport are spontaneous because they result in an increase in entropy of the system.

4

Which compound could be most easily modified to form ATP?
1) the RNA nucleotide adenosine
2) the amino acid tryptophan
3) the DNA nucleotide adenosine
4) the nitrogenous base adenine
5) the monosaccharide ribose

1

Much of the suitability of ATP as an energy intermediary is related to the instability of the bonds between the phosphate groups. These bonds are unstable because _____.
1) the valence electrons in the phosphorus atom have less energy on average than those of other atoms
2) the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP
3) they are hydrogen bonds, which are only about 10% as strong as covalent bonds
4) the phosphate groups are polar and are attracted to the water in the cell's interior
5) the bonds between the phosphate groups are unusually strong and breaking them releases free energy

2

When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations?
1) Cells are less efficient at energy metabolism than reactions that are optimized in a test tube.
2) The amount of heat released by a reaction has nothing to do with the free energy change of the reaction.
3) In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.
4) In cells, ATP is hydrolyzed to ADP and Pi, but in the test tube it is hydrolyzed to carbon dioxide and water.
5) Cells have the ability to store heat; this cannot happen in a test tube.

3

What best characterizes the role of ATP in cellular metabolism?
1) The release of free energy during the hydrolysis of ATP heats the surrounding environment.
2) The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate.
3) It is catabolized to carbon dioxide and water.
4) The DG associated with its hydrolysis is positive.
5) The charge on the phosphate group of ATP tends to make the molecule very water-soluble.

2

The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways?
1) the conversion of glucose + fructose to make sucrose
2) the contraction of a muscle cell
3) the hydrolysis of ATP
4) the active transport of a phosphate ion into the cell
5) the formation of ATP from ADP + Pi

3

A chemical reaction is designated as exergonic rather than endergonic when _____.
1) activation energy is required
2) the products are less complex than the reactants
3) activation energy exceeds net energy release
4) the potential energy of the products is less than the potential energy of the reactants
5) it absorbs more energy

4

What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction?
1) The sign determines whether the reaction is spontaneous, and the magnitude determines the speed.
2) The sign does not matter, but the larger the magnitude of ΔG the faster the reaction.
3) The sign does not matter, but the smaller the magnitude of ΔG the faster the reaction.
4) The more negative the ΔG, the faster the reaction is.
5) Neither the sign nor the magnitude of ΔG have anything to do with the speed of a reaction.

5

The mechanism of enzyme action is _____.
1) providing energy to speed up the rate of the reaction
2) lowering the energy of activation for a reaction
3) changing the direction of thermodynamic equilibrium
4) changing endergonic into exergonic reactions
5) lowering the free energy change of a reaction

2

Which of the following statements about enzymes is true?
1) Enzymes increase the rate of a reaction by raising the activation energy for reactions.
2) Enzymes react with their substrate (form chemical bonds) forming an enzyme-substrate complex, which irreversibly alters the enzyme.
3) Enzymes speed up the rate of the reaction without changing the DG for the reaction.
4) The more heat that is added to a reaction, the faster the enzymes will function.
5) all of the above

3

Which of the following statements about enzyme function is correct?
1) Enzymes can greatly speed up reactions, but they cannot change the net energy output because they cannot change the activation energy.
2) Enzymes can change the equilibrium point of reactions, but they cannot speed up reactions because they cannot change the net energy output.
3) Enzymes can greatly speed up reactions, but they cannot change the activation energy because they cannot change the net energy output.
4) Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output.
5) none of the above

4

A plot of reaction rate (velocity) against temperature for an enzyme indicates little activity at 10°C and 45°C, with peak activity at 35°C. The most reasonable explanation for the low velocity at 10°C is that _____.
1) the hydrogen bonds that define the structure of the enzyme's active site are unstable
2) the substrate becomes a competitive inhibitor at lower temperature
3) the enzyme was denatured
4) the cofactors required by the enzyme system lack the thermal energy required to activate the enzyme
5) there is too little activation energy available

5

Which of the following statements about enzymes is correct?
1) Most enzymes are proteins.
2) An enzyme is not consumed by the catalytic process.
3) An enzyme is very specific in terms of which substrate it binds to.
4) An enzyme lowers the activation energy of a chemical reaction.
5) all of the above

5

Which of the following statements about the active site of an enzyme is correct?
1) The active site has a fixed structure (shape).
2) Coenzymes are never found in the active site of an enzyme.
3) The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.
4) The structure of the active site is not affected by changes in temperature.
5) The active site allows the reaction to occur under the same environmental conditions as the reaction without the enzyme.

3

What is meant by the "induced fit" of an enzyme?
1) The substrate can be altered so that it is induced to fit into the enzyme's active site.
2) The enzyme structure is altered so that it can be induced to fit many different types of substrate.
3) The presence of the substrate in solution induces the enzyme to slightly change its structure.
4) The shape of the active site is nearly perfect for specifically binding the enzyme's substrate(s).
5) The enzyme changes its shape slightly as the substrate binds to it.

5

Which of the following statements correctly describe(s) the role(s) of heat and temperature in biological reactions?
1) Heat from the environment is necessary for substrates to get over the activation energy barrier.
2) Increasing temperature increases the kinetic energy of the substrates.
3) Increasing the temperature will increase the rate of enzyme-catalyzed reactions.
4) The first and second choices are correct.
5) The first, second, and third choices are correct.

4

Above a certain substrate concentration, the rate of an enzyme-catalyzed reaction drops as the enzymes become saturated. Which of the following would lead to a faster conversion of substrate into product under these saturated conditions?
1) an increase in concentration of enzyme
2) increasing the temperature by a few degrees
3) increasing the substrate concentration
4) The first and second choices are correct.
5) The first, second, and third choices are correct.

4

Which of the following environments or actions affect(s) the rate of an enzyme reaction?
1) heating the enzyme
2) cooling the enzyme
3) substrate concentration
4) pH
5) all of the above

5

Enzyme activity is affected by pH because _____.
1) most substrates don't function well at high or low pH
2) high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site
3) low pH will denature all enzymes
4) changes in pH can cause loss of cofactors from the enzyme
5) the binding of hydrogen ions to the enzyme absorbs energy and thus there may not be enough energy to overcome the activation energy barrier

2

Which of these statements about enzyme inhibitors is true?
1) A competitive inhibitor binds to the enzyme at a place that is separate from the active site.
2) The action of competitive inhibitors may be reversible or irreversible.
3) A noncompetitive inhibitor does not change the shape of the active site.
4) When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback.
5) Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory.

2

Succinylcholine is structurally almost identical to acetylcholine. If succinylcholine is added to a mixture that contains acetylcholine and the enzyme that hydrolyzes acetylcholine (but not succinylcholine), the rate of acetylcholine hydrolysis is decreased. Subsequent addition of more acetylcholine restores the original rate of acetylcholine hydrolysis. Which of the following correctly explains this observation?
1) Succinylcholine must be a competitive inhibitor with acetylcholine.
2) Succinylcholine must be an allosteric regulator for this enzyme.
3) The active site must have the wrong configuration to permit succinylcholine binding.
4) Succinylcholine must be a non-competitive inhibitor.
5) The activation energy barrier for succinylcholine hydrolysis is higher than for acetylcholine hydrolysis.

1

The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of _____.
1) feedback inhibition
2) competitive inhibition
3) allosteric regulation
4) non-competitive inhibition
5) cooperativity

3

Which of the following statements about allosteric proteins is/are true?
1) They are sensitive to environmental conditions.
2) They are acted on by inhibitors.
3) They exist in active and inactive conformations.
4) all of the above
5) none of the above

4

The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Which of the following best explains why this decrease occurs?
1) The allosteric inhibitor binds to the active site, preventing the substrate from binding.
2) The allosteric inhibitor causes free energy change of the reaction to increase.
3) The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site.
4) The allosteric inhibitor lowers the temperature of the active site.
5) The allosteric inhibitor binds to the substrate and prevents it from binding at the active site.

3

Under most conditions, the supply of energy by catabolic pathways is regulated by the demand for energy by anabolic pathways. Considering the role of ATP formation and hydrolysis in energy coupling of anabolic and catabolic pathways, which of the following statements is most likely to be true?
1) High levels of ADP act as an allosteric inhibitor of catabolic pathways.
2) High levels of ATP act as an allosteric activator of anabolic pathways.
3) High levels of ATP act as an allosteric activator of catabolic pathways.
4) High levels of ADP act as an allosteric activator of catabolic pathways
5) High levels of ADP act as an allosteric inhibitor of anabolic pathways.

4

Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as ___________ is to ___________.
1) exergonic; spontaneous
2) exergonic; endergonic
3) free energy; entropy
4) work; energy
5) entropy; enthalpy

2

Most cells cannot harness heat to perform work because
1) heat is not a form of energy.
2) cells do not have much heat; they are relatively cool.
3) temperature is usually uniform throughout a cell.
4) heat can never be used to do work.
5) heat must remain constant during work.

3

Which of the following metabolic processes can occur without a net influx of energy from some other process?
1) ADP + Pi → ATP + H2O
2) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
3) 6 CO2 + 6 H2O → C6H12O6 + 6 O2
4) amino acids → protein
5) glucose + fructose → sucrose

2

If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to
1) add more of the enzyme.
2) heat the solution to 90°C.
3) add more substrate.
4) add an allosteric inhibitor.
5) add a noncompetitive inhibitor.

1

If an enzyme is added to a solution where its substrate and product are in equilibrium, what would occur?
1) Additional product would be formed.
2) Additional substrate would be formed.
3) The reaction would change from endergonic to exergonic.
4) The free energy of the system would change.
5) Nothing; the reaction would stay at equilibrium.

5

Some bacteria are metabolically active in hot springs because
1) they are able to maintain a lower internal temperature.
2) high temperatures make catalysis unnecessary.
3) their enzymes have high optimal temperatures.
4) their enzymes are completely insensitive to temperature.
5) they use molecules other than proteins or RNAs as their main catalysts.

3

Using a series of arrows, draw the branched metabolic reaction pathway described by the following statements, and then answer the question at the end. Use red arrows and minus signs to indicate inhibition.
L can form either M or N.
M can form O.
O can form either P or R.
P can form Q.
R can form S.
O inhibits the reaction of L to form M.
Q inhibits the reaction of O to form P.
S inhibits the reaction of O to form R.

Which reaction would prevail if both Q and S were present in the cell in high concentrations?
1) L → M
2) M → O
3) L → N
4) O → P
5) R → S

3

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