Question 1

Which of the following metabolic processes can occur without a net influx of energy from some other process?
A)ADP + Pi → ATP + H₂O
B)C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O
C)6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂
D)amino acids → protein
E)glucose + fructose → sucrose

Accepted Answer

The process described in option B is cellular respiration, which is an exergonic reaction that releases energy, meaning it does not require a net influx of energy to occur.

Question 2

An important group of peripheral membrane proteins are enzymes, such as the phospholipases that attack the head groups of phospholipids leading to the degradation of damaged membranes. What properties must these enzymes exhibit?
A)resistance to degradation
B)independence from cofactor interaction
C)water solubility
D)lipid solubility
E)membrane spanning domains

Accepted Answer

Peripheral membrane proteins, like phospholipases, must be water-soluble to function in the aqueous environment of the cytosol and interact with the membrane surface.

Question 3

Most cells cannot harness heat to perform work because
A)heat is not a form of energy.
B)cells do not have much heat; they are relatively cool.
C)temperature is usually uniform throughout a cell.
D)heat can never be used to do work.
E)heat denatures enzymes.

Accepted Answer

Temperature is usually uniform throughout a cell, which means there is no temperature gradient that can be harnessed to perform work. Heat can be a form of energy, but without a temperature differential, it is not a useful source of energy for cells.

Question 4

The following questions are based on the reaction A + B → C + D shown in Figure 8.2.

-Which of the following statements describes enzyme cooperativity?
A)A multi-enzyme complex contains all the enzymes of a metabolic pathway.
B)A product of a pathway serves as a competitive inhibitor of an early enzyme in the pathway.
C)A substrate molecule bound to an active site affects the active site of several subunits.
D)Several substrate molecules can be catalyzed by the same enzyme.
E)A substrate binds to an active site and inhibits cooperation between enzymes in a pathway.

Accepted Answer

Enzyme cooperativity occurs when a substrate molecule bound to an active site affects the active site of several subunits, causing them to change their shape and become more or less receptive to substrate binding. This results in increased or decreased activity of the enzyme complex, respectively. Choices A and B describe other forms of enzyme regulation, while choices D and E do not relate to cooperativity specifically.

Question 5

Which of the following is an example of cooperativity?
A)the binding of an end product of a metabolic pathway to the first enzyme that acts in the pathway
B)protein function at one site affected by binding at another of its active sites
C)a molecule binding at one unit of a tetramer allowing faster binding at each of the other three
D)the effect of increasing temperature on the rate of an enzymatic reaction
E)binding of an ATP molecule along with one of the substrate molecules in an active site

Accepted Answer

Cooperativity is when binding at one site of a protein affects binding or activity at another site. In this case, the binding of a molecule at one unit of a tetramer (a protein made up of four subunits) affects binding at the other three subunits, allowing for faster binding overall. This is an example of positive cooperativity.

Question 6

Use Figure 8.3 to answer the following questions.
 
-In coupled reactions, in which direction would the endergonic reaction be driven relative to the clockwise direction of the ATP reaction above and shown in the figure?
A)from left to right at the top of the figure
B)under the symbol for energy doing cellular work in the figure
C)from right to left at the bottom of the figure
D)it would be shown separately after the figure
E)it would be shown in a clockwise direction at the top of the figure

Accepted Answer

The answer of Use Figure 8.3 to answer the following...

Question 7

The following questions are based on the reaction A + B → C + D shown in Figure 8.2.

-How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?
A)by binding at the active site of the enzyme
B)by changing the shape of a reactant
C)by changing the free energy change of the reaction
D)by acting as a coenzyme for the reaction
E)by decreasing the activation energy of the reaction

Accepted Answer

A noncompetitive inhibitor binds to a site other than the active site of the enzyme, changing the shape of the enzyme and making it less efficient in catalyzing the reaction. This can decrease the rate of the reaction by slowing down the formation of the product(s).

Question 8

Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as __________ is to __________.
A)exergonic; spontaneous
B)exergonic; endergonic
C)free energy; entropy
D)work; energy
E)entropy; enthalpy

Accepted Answer

Catabolism involves breaking down molecules and is therefore exergonic (releases energy), while anabolism involves building molecules and is therefore endergonic (requires energy). The only pair of choices that reflect this relationship is (B) exergonic; endergonic.

Question 9

Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
A)cessation of all enzyme formation
B)compartmentalization of enzymes into defined organelles
C)exporting enzymes out of the cell
D)connecting enzymes into large aggregates
E)hydrophobic interactions

Accepted Answer

Compartmentalization of enzymes into defined organelles allows cells to control enzymatic activity by isolating specific reactions and pathways, thus regulating the environment in which enzymes operate.

Question 10

The following questions are based on the reaction A + B → C + D shown in Figure 8.2.

-The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is known as
A)metabolic inhibition.
B)feedback inhibition.
C)allosteric inhibition.
D)noncooperative inhibition.
E)reversible inhibition.

Accepted Answer

The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is known as feedback inhibition. This is the only option given that accurately describes this mechanism. Choice A, metabolic inhibition, is not a specific term and could refer to a variety of different mechanisms. Choice C, allosteric inhibition, is a mechanism in which an inhibitor binds to a site on an enzyme that is different from the active site, causing a conformational change that reduces the enzyme's activity. This is not necessarily the same as feedback inhibition. Choice D, noncooperative inhibition, and choice E, reversible inhibition, do not accurately describe the mechanism of feedback inhibition.

Question 11

Some enzymatic regulation is allosteric. In such cases, which of the following would usually be found?
A)cooperativity
B)feedback inhibition
C)both activating and inhibitory activity
D)an enzyme with more than one subunit
E)the need for cofactors

Accepted Answer

An enzyme with more than one subunit is usually found in allosteric regulation. Allosteric enzymes are typically composed of multiple subunits, and the binding of a ligand to one subunit can affect the activity of the other subunits.

Question 12

Some bacteria are metabolically active in hot springs because
A)they are able to maintain a cooler internal temperature.
B)high temperatures make catalysis unnecessary.
C)their enzymes have high optimal temperatures.
D)their enzymes are completely insensitive to temperature.
E)they use molecules other than proteins or RNAs as their main catalysts.

Accepted Answer

Bacteria in hot springs have evolved enzymes with higher optimal temperatures to maintain metabolic activity in their extreme environment.

Question 13

Use Figure 8.3 to answer the following questions.
 
-Which of the following is the most correct interpretation of the figure?
A)Inorganic phosphate is created from organic phosphate.
B)Energy from catabolism can be used directly for performing cellular work.
C)ADP + Pi are a set of molecules that store energy for catabolism.
D)ATP is a molecule that acts as an intermediary to store energy for cellular work.
E)Pi acts as a shuttle molecule to move energy from ATP to ADP.

Accepted Answer

The figure shows the conversion of ATP to ADP and Pi, and then the conversion of ADP and Pi back to ATP with the input of energy. This illustrates that ATP acts as an intermediary to store energy for cellular work, as it can donate a phosphate group to perform work and then be regenerated through the addition of a phosphate group and energy from catabolism.

Question 14

Using a series of arrows, draw the branched metabolic reaction pathway described by the following statements, then answer the question at the end.
∙ 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?
A)L → M
B)M → O
C)L → N
D)O → P
E)R → S

Accepted Answer

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Question 15

Among enzymes, kinases catalyze phosphorylation, while phosphatases catalyze removal of phosphate(s). A cell's use of these enzymes can therefore function as an on-off switch for various processes. Which of the following is probably involved?
A)the change in a protein's charge leading to a conformational change
B)the change in a protein's charge leading to cleavage
C)a change in the optimal pH at which a reaction will occur
D)a change in the optimal temperature at which a reaction will occur
E)the excision of one or more peptides

Accepted Answer

Phosphorylation, which is catalyzed by kinases, involves the addition of a phosphate group to a protein. This can change the charge of the protein and lead to a conformational change, which in turn can turn a process on or off. Similarly, removal of a phosphate group by phosphatases can change the charge and conformation of a protein, thereby regulating a biological process. Therefore, option A is the best answer. The other options (B, C, D, and E) are not directly related to the action of kinases and phosphatases.

Question 16

If an enzyme solution is saturated with substrate, the most effective way to obtain a faster yield of products is to
A)add more of the enzyme.
B)heat the solution to 90°C.
C)add more substrate.
D)add an allosteric inhibitor.
E)add a noncompetitive inhibitor.

Accepted Answer

If the substrate is saturated, it means all the enzyme molecules are already bound to substrate molecules. Therefore, the addition of more substrate will not increase the rate of reaction. On the other hand, adding more enzyme molecules will allow more substrate molecules to be bound and converted to products, thus increasing the rate of reaction. Heat, allosteric inhibitors, and noncompetitive inhibitors can all have negative effects on enzyme activity and may decrease the rate of product yield.

Question 17

The following questions are based on the reaction A + B → C + D shown in Figure 8.2.

-What is substance X?
A)a coenzyme
B)an allosteric inhibitor
C)a substrate
D)an intermediate
E)the product

Accepted Answer

Substance X is the substrate that is converted to Y by the enzyme.

Answer: B
 Product A binding to the enzyme at a position remote from its active site indicates that it is an allosteric inhibitor, as it is affecting the enzyme's activity through an allosteric site rather than directly at the active site.

Question 18

The following questions are based on the reaction A + B → C + D shown in Figure 8.2.

-Substance A functions as
A)a coenzyme.
B)an allosteric inhibitor.
C)the substrate.
D)an intermediate.
E)a competitive inhibitor.

Accepted Answer

Substance A functions as an allosteric inhibitor, which means it binds to an enzyme at a site other than the active site, causing a change in the enzyme's shape and reducing its activity.

Question 19

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

Accepted Answer

The enzyme would not be able to shift the equilibrium and therefore the reaction would remain at equilibrium. Enzymes do not affect the equilibrium constant of a reaction, they only increase the rate of the reaction to reach equilibrium more quickly.

Quiz 8: An Introduction to Metabolism

Which of the following metabolic processes can occur without a net influx of energy from some other process?

An important group of peripheral membrane proteins are enzymes, such as the phospholipases that attack the head groups of phospholipids leading to the degradation of damaged membranes. What properties must these enzymes exhibit?

Most cells cannot harness heat to perform work because

The following questions are based on the reaction A + B → C + D shown in Figure 8.2. -Which of the following statements describes enzyme cooperativity?

Which of the following is an example of cooperativity?

Use Figure 8.3 to answer the following questions. -In coupled reactions, in which direction would the endergonic reaction be driven relative to the clockwise direction of the ATP reaction above and shown in the figure?

The following questions are based on the reaction A + B → C + D shown in Figure 8.2. -How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?

Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as is to .

Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?

The following questions are based on the reaction A + B → C + D shown in Figure 8.2. -The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is known as

Some enzymatic regulation is allosteric. In such cases, which of the following would usually be found?

Some bacteria are metabolically active in hot springs because

Use Figure 8.3 to answer the following questions. -Which of the following is the most correct interpretation of the figure?

Among enzymes, kinases catalyze phosphorylation, while phosphatases catalyze removal of phosphate(s) . A cell's use of these enzymes can therefore function as an on-off switch for various processes. Which of the following is probably involved?

If an enzyme solution is saturated with substrate, the most effective way to obtain a faster yield of products is to

The following questions are based on the reaction A + B → C + D shown in Figure 8.2. -What is substance X?

The following questions are based on the reaction A + B → C + D shown in Figure 8.2. -Substance A functions as

If an enzyme is added to a solution where its substrate and product are in equilibrium, what would occur?