Chapter 8 Homework
|Under what conditions could some exothermic (ΔH<0) reactions be nonspontaneous (ΔG>0)?|
A) The overall reaction reduces entropy (products have less entropy than reactants).
|A) The overall reaction reduces entropy (products have less entropy than reactants).|
|When is the overall free energy change ΔG in a reaction most likely to be negative (meaning that the reaction is exergonic)?|
A) When products have higher potential energy and higher entropy than reactants
|D) When products have lower potential energy and higher entropy than reactants|
|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?|
A) Living organisms do not follow the laws of thermodynamics.
|D) As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.|
|What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?|
A) Dehydration synthesis
Hydrolysis involves breaking bonds with the addition of water.
|In general, enzymes are what kinds of molecules?|
Enzymes are proteins.
|Enzymes work by _____.|
A) Reducing EA
|A) Reducing EA|
Enzymes work by reducing the energy of activation
|An enzyme _____.|
A) Is a inorganic catalyst
|C) Is an organic catalyst|
Enzymes are proteins that behave as catalysts.
|What name is given to the reactants in an enzymatically catalyzed reaction?|
This is the name given to the reactants in an enzymatically catalyzed reaction.
|As a result of its involvement in a reaction, an enzyme _____.|
A) Is unchanged
|A) Is unchanged|
Enzymes are not changed as a result of their participation in a reaction.
|What is the correct label for “A”?|
|B) Energy of activation|
The energy of activation must be overcome in order for a reaction to proceed.
|Can an enzyme make a nonspontaneous reaction occur spontaneously? Why or why not?|
A) No, because enzymes do not lower the activation energy of the reaction.
|C) No, because enzymes do not affect the overall ΔG of a reaction.|
|You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct?|
A) Either the enzyme has two distinct active sites or the reactants involved in the two reactions are very similar in size and shape.
|A) Either the enzyme has two distinct active sites or the reactants involved in the two reactions are very similar in size and shape.|
|The lock-and-key analogy for enzymes applies to the specificity of enzymes _____.|
A) As they form their tertiary structure
|B) Binding to their substrate|
|Complete this vocabulary exercise relating to the three types of enzyme inhibitors.|
Drag the words on the left to the appropriate blanks in the sentences on the right. Each word is used only once.
|Competitive inhibitors compete physically and structurally with the substrate for an enzyme’s active site; they can be outcompeted by adding extra substrate. Noncompetitive inhibitors do not compete for the active site, but inhibit the enzyme by binding elsewhere and changing the enzyme’s shape. Irreversible inhibitors bind directly to the active site by covalent bonds, which change the structure of the enzyme and inactivate it permanently. Most medications are enzyme inhibitors of one kind or another.|
|A(n) ________ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate.||competitive|
|A(n) ________ inhibitor binds to a site on the enzyme that is not the active site.||noncompetitive|
|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|
|The competitive inhibitor competes with the substrate for the _________ on the enzyme.||active site|
|When the noncompetitive inhibitor is bonded to the _________, the shape of the enzyme is distorted.||enzyme|
|Enzyme inhibitors disrupt normal interactions between an enzyme and its _________.||substrate|
|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?
A) Removing the irreversible inhibitor should get the reaction working again.
|B) The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.|
Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive. Some drugs are irreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).
|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?
A) Add more inhibitor to speed up the reaction.
|B) Add more substrate; it will outcompete the inhibitor and increase the reaction rate.|
Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor. Many drugs used to treat different medical conditions, including hypertension, are competitive inhibitors. It is fairly easy to make a molecule that is similar in structure to a particular substrate because the known enzyme’s shape can be used as a model of what the molecule needs to look like. It is more difficult to make a noncompetitive inhibitor because it is less obvious what the noncompetitive inhibitor’s shape and structure should be.
|An enzyme inhibitor that is roughly the same shape as the substrate and binds at the active site is termed a(n) _____ inhibitor.|
Competitive inhibitors prevent substrate binding by mimicking the substrate and competing for the active site.
|A noncompetitive inhibitor decreases the rate of an enzyme reaction by _____.|
A) Acting as a coenzyme for the reaction
|E) Changing the shape of the enzyme’s active site|
|How might a change of one amino acid at a site, distant from the active site of an enzyme, alter an enzyme’s substrate specificity?|
A) By changing the enzyme’s pH optimum
|B) By changing the shape of an enzyme|
|What is a transition state?|
A) The place where an allosteric regulatory molecule binds to an enzyme
|D) The complex formed as covalent bonds are being broken and re-formed during a reaction|
|If you were to expose glucose to oxygen on your lab bench, why would you not expect to see it burn as shown in the figure below?|
A) Energy is required for the sugar and oxygen to reach their transition state.
|A) Energy is required for the sugar and oxygen to reach their transition state.|