Question 1

A worker in a chemical factory falls into a vat with pentachlorophenol, a wood preservative that uncouples oxidative phosphorylation and that can be absorbed through the skin.Which of the following anomalies can you expect as a result (while the patient is still alive)?

A)Hypothermia (reduced body temperature), because mitochondrial energy generation is impaired.
B)A slowdown of all catabolic pathways, including glycolysis.
C)All redox couples in the respiratory chain will be trapped in the reduced state.
D)Glycogen phosphorylase is activated.
E)ATP can no longer be synthesized from carbohydrates, but ATP synthesis from fatty acids is intact.

Glycogen phosphorylase is activated.

Accepted Answer

Extrahepatic glycogen phosphorylase is allosterically activated by adenosine monophosphate (AMP).Therefore, it becomes active whenever the cellular energy charge is low.

Question 2

The liver converts a molecule of citric acid, obtained from lemon juice, into succinyl-coenzyme A (CoA).Succinyl-CoA is subsequently used for heme biosynthesis.Approximately, how many ATP (and GTP) molecules can be derived from the conversion of one molecule of citrate to succinyl-CoA?

A)3.
B)6.
C)7.
D)9.
E)12.

6.

Accepted Answer

One molecule of NADH is formed by isocitrate dehydrogenase, and another one by α-ketoglutarate dehydrogenase.Each NADH molecule produces about three ATP molecules during oxidative phosphorylation.

Question 3

Dental plaque contains bacteria that produce lactic acid from glucose.Lactic acid is sufficiently acidic to dissolve calcium phosphates in tooth enamel, and this contributes to dental caries (cavities).Which of the following enzymes does the fluoride in toothpaste inhibit in the cariogenic bacterium Streptococcus mutans, thereby reducing lactic acid production on the enamel surface of teeth?

A)Hexokinase.
B)Glucose-6-phosphate isomerase.
C)Aldolase.
D)Enolase.
E)Pyruvate kinase.

Enolase.

Accepted Answer

Enolase is the only fluoride-sensitive enzyme in glycolysis.

Question 4

At the funeral of the worker, some of the mourners become severely ill after eating cassava puree, which still contained toxic quantities of cyanide as a result of improper processing of the cassava root.Which abnormalities do you expect in these patients?

A)Cyanosis, caused by reduced oxygen saturation of hemoglobin.
B)Reduced activity of phosphofructokinase-1.
C)Lactic acidosis.
D)The P/O ratio for the mitochondrial oxidation of NADH is reduced.
E)Hypoventilation.

Accepted Answer

Low energy charge activates both glycogen phosphorylase and phosphofructokinase-1.The pyruvate thus formed cannot be oxidized by the mitochondria and is diverted into lactate.

Question 5

Another molecule of citric acid from the same glass of lemon juice is converted to oxaloacetate, which is subsequently processed into glucose.How many molecules of ATP and/or GTP do the reactions from citrate to oxaloacetate produce, either directly or indirectly through the respiratory chain?

A)3.
B)6.
C)7.
D)9.
E)12.

Accepted Answer

NADH is produced by isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase.Flavin adenine dinucleotide (FAD) is produced by succinate dehydrogenase, and GTP by succinyl-CoA synthetase.Assuming an ATP yield of three molecules for NADH and two for the reduced form of flavin adenine dinucleotide (FADH₂), this adds up to 11 ATP and 1 GTP.

Question 6

A research group reported that transgenic mice overexpressing the human catalase gene in mitochondria have a 5-month increase in median lifespan.What is the substrate and the coenzyme for the human catalase enzyme, respectively?

A)Superoxide anion; ATP.
B)Hydrogen peroxide; heme.
C)Organic peroxy radicals; thiamine pyrophosphate.
D)Hydroxyl radicals; flavin mononucleotide (FMN).
E)Coenzyme Q; NADH.

Accepted Answer

Catalase is a heme enzyme that decomposes hydrogen peroxide.

Question 7

Thiamine deficiency leads not only to the accumulation of pyruvate and lactate but also to the accumulation of:&#10;A)Succinyl-CoA.&#10;B)Oxaloacetate.&#10;C)Malate.&#10;D)Succinate.&#10;E)&#945;-Ketoglutarate.

Accepted Answer

α-Ketoglutarate dehydrogenase is the only TCA cycle enzyme that contains thiamine pyrophosphate.

Question 8

Complete the following phrase by filling in the blanks to make it a true statement."The action of the inhibitor rotenone on the Complex I enzyme system of electron transport results in accumulation of _____, which slows down _____.This results in ______."

A)The reduced form of nicotinamide adenine dinucleotide (NADH); adenosine triphosphate (ATP) synthesis; glycogen accumulation.
B)Nicotinamide adenine dinucleotide (NAD+); glycolysis; a higher membrane potential across the inner mitochondrial membrane.
C)NAD+; ATP synthesis; enhanced fatty acid biosynthesis.
D)NADH; the tricarboxylic acid (TCA) cycle; accumulation of lactate.
E)NAD+; the TCA cycle; enhanced gluconeogenesis.

Accepted Answer

The high NADH/NAD⁺ ratio inhibits the dehydrogenases of the TCA cycle.Lactate accumulates because glycogen breakdown and glycolysis are stimulated by low energy charge, pyruvate cannot be oxidized by the mitochondria, and the equilibrium of the lactate dehydrogenase reaction is far on the side of lactate when the NADH/NAD⁺ ratio is high.

Question 9

Streptococcus pneumoniae is the primary cause of community-acquired pneumonia.In blood plasma, the transcription of the phosphofructokinase-1 gene in S.pneumoniae is reduced to 20% of baseline.If glycolysis is similar in S.pneumoniae and Homo sapiens, what is most likely to result from reduced transcription of the phosphofructokinase-1 gene in the bacteria?

A)Glucose utilization increases.
B)Glucose production from lactate is reduced.
C)The rate of lactate formation increases.
D)The amount of glyceraldehyde-3-phosphate increases.
E)The amount of fructose-6-phosphate increases.

Accepted Answer

Everything else being equal, the substrate of the enzyme (fructose-6-phosphate) accumulates when the enzyme activity is reduced.

Deck 21: Glycolysis, Tricarboxylic Acid Cycle, and Oxidative Phosphorylation