BRS Biochemistry - Carbohydrate Metabolism Flashcards
Allopurinol is used in the treatment of gout because of its ability to inhibit xanthine oxidase. This inhibition makes it impossible for the enzyme to degrade xanthin and hypoxanthine, which reduces the synthesis of urate, the culprit of gout. Allopurinol works through which one of the following mechanisms?
A. Suicide inhibition B. noncompetitive inhibition C. Allosteric interaction with the enzyme that increases Vmax D. Feedback inhibition E. Subunit cooperativity
A - Allopurinol is a substrate for xanthine oxidase, which converts allpurinol to oxypurinol, and which binds tightly to the enzyme and is not released. This is an example of irreversible suicide inhibition, which leads to a decrease of Vmax.
A 10-year old boy presents with vomiting, sweating, drooling and a decreased heart rate. He was sprayed by an organophosphate derivative that covalently binds to acetylcholinesterase and inactivates the enzyme. What type of inhibition is displayed?
A. Competitive B. Noncompetitive C. Irreversible D. Feedback E. Allosteric
C - This is an example of irreversible inhibition because a covalent bond has been formed between the inhibitor and the required serine at the active site of the enzyme.
Note: this enzyme can only be reactivated if that covalent bond is hydrolyzed.
A patient with ataxia, increased confusion, and new-onset short-term memory loss also has a lateral rectus muscle palsy. Which is correct about his condition?
A. It is the result of irreversible inhibition
B. It cannot be effectively treated
C. It is the result of noncompetitive inhibition
D. It is the result of competitive inhibition
D. It is the result of competitive inhibition
E. It is due to the lack of a fundamental coenzyme
E - Patient has classic symptoms of Wernicke encephalopathy, which results from an inadequate intake or absorption of thiamine.
Acetazolamide is a noncompetitive inhibitor of carbonic anhydrase and, therefore, will lead to which of the following concerning the kinestic constants of carbonic anhydrase?
A. An increase in Km B. A decrease in m C. An increase in Vmax D. A decrease in Vmax E. A decrease in both Km and Vmax
D - a noncompetitive inhibitor binds to the enzyme at a site different than where the substrate binds. This decreases the number of enzymes capable of catalyzing the reaction, decreasing Vmax.
Dilantin is a substrate that binds to and is metabolized by an enzyme in the liver. Which one of the following statements best describes the relationship between an enzyme, substrate, and product?
A. Enzyme-product complexes enhance substrate binding
B. All the active sites of the enzyme are saturated with substrate at high substrate concentrations
C. At high substrate concentrations, none of the enzyme is found in the ES complex
D. At low substrate concentrations, none of the enzyme is found in the ES complex
E. Significant produce formation results in activation of the reaction
B - the rate of an enzyme-catalyzed reaction will generally increase exponentially with respect to substrate concentration until the substrate concentration exhausts the catalytic sites of the enzyme population (i.e. Vmax)
A patient who is lactose-intolerant lacks the ability to cleave which one of the following glycosidic bonds?
A. Glucose-a (1-->4) glucose B. Glucose-a (1-->2) fructose C. Galactose-B (1-->4) glucose D. Glucose-a (1-->6) glucose E. Glucose-B (1-->4) glucose
C - the vignette is a classic presentation of lactase deficiency. Latase is an intestinal enzyme that cleaves the B(1–>4) linkage of lactose, releasing galactose and glucose.
What type of transport mechanism does glucose utilize for gastrointestinal absorption?
A. Passive B. Facilitated C. Active D. Passive and facilitated E. Active and facilitated
E - Glucose absorption in the small intestine occurs via two types of transport. The first is facilitate transport (passive via concentration gradient0 and the second is active transport (requires energy, usually in the form of ATP).
Which of the following glycosidic bonds prevents humans from completely digesting fiber?
A. Glucose-a (1-->4) glucose B. Glucose-a (1-->6) glucose C. Glucose-B (1-->4) glucose D. Glucose-a (1-->B2) fructose E. Galactose-B (1-->4) glucose
B - The glucose B (1–>4) glucose glycosidic bond, found in cellulose, a major component of fiber, cannot be digested by human enzymes.
