Biochemistry and Bioenergetics: ATP, Metabolism, and Enzyme Function

ATP is the cells major chemical form of energy, and often is converted to ADP during reactions, thereby releasing energy to allow the reaction to proceed in the forward direction. The highest-energy phosphate bond in ATP is located between which of the following groups?

Two phosphate groups

All cells require energy to survive, and the laws of thermodynamics need to be followed within biologic systems. Which one of the following bioenergetic terms or phrases is defined correctly?

The change in enthalpy of a reaction is a measure of the total amount of heat that can be released from changes in the chemical bonds.

In order for a cell to carry out its biologic functions, the intracellular reactions need to be directed to follow a certain pathway. Which one statement below best describes the direction a chemical reaction will follow?

A reaction with positive free energy will proceed in the forward direction if the substrate concentration is raised high enough.

Mr. P. has just suffered a heart attack. As a consequence, his heart will display which one of the following changes?

Increased intracellular H+ concentration

Many biologic reactions are oxidation-reduction reactions that utilize a biologic electron carrier. Which one of the following statements correctly describes reduction of one of these electron carriers, NAD+ or FAD?

NAD+ accepts two electrons as a hydride ion to form NADH.

Active transport is necessary to move compounds into or out of the cell or mitochondria. Transport work can occur when ATP donates its phosphate group to a transport protein, thereby altering the conformation of that protein. Which one of the following mechanisms allows this conformational change to occur?

A gain of ionic interactions, which alter tertiary and/or quaternary structure of the protein

Given the ΔGo′ values below, determine the overall ΔGo′ for the following reaction: Creatine + ATP → creatine-phosphate + ADP

+3.0 kcal/mol

When athletes expend vast amounts of energy, they are sometimes seen on the sidelines using supplemental oxygen. More than 90% of the oxygen we breathe is used for the generation of which one of the following?

ATP

ATP is the cells major energy-carrying molecule, and in order for a cell to survive, the cell must be able to regenerate ATP when ATP levels drop. Which one of the following statements accurately describes an aspect of ATP metabolism?

Phosphate groups repel each other, which in ATP leads to strained bond formation.

All physiologic processes in living cells require energy transformation. Which one of the following would be considered biochemical work utilizing the high-energy phosphate bonds of ATP?

Converting toxic compounds to nontoxic compounds in the liver

Consider the reaction A → B. The ΔGo′ for this reaction is +1.8 kcal/mol. If the concentration of B is, at equilibrium, 1.0 mM, what would be the concentration of A at equilibrium, at 25°C?

20 mM

What would be the standard free energy change for the conversion of D → A in the given reactions?

−1.18 kcal/mol

The enzyme that catalyzes the reaction RH + O2 + NADPH + H+ → R-OH + H2O + NADP+ is best classified as which of the following?

Oxygenase

The free-energy change for the reaction FAD(2H) + ½ O2 → FAD + H2O is which one of the following?

−47.7 kcal/mol

What is the order of energy yield (from most energy to least energy) when the three given fatty acids are oxidized completely to carbon dioxide and water?

i > ii > iii

Glucose is the body's universal fuel, which can be utilized by virtually all tissues. A major role of glycolysis is which one of the following?

To generate energy

Starting with glyceraldehyde 3-phosphate and synthesizing one molecule of pyruvate, the net yield of ATP and NADH would be which one of the following?

2 ATP, 1 NADH

When glycogen is degraded, glucose 1-phosphate is formed. Starting with glucose 1-phosphate and ending with two molecules of pyruvate, what is the net yield of glycolysis in terms of ATP and NADH formed?

3 ATP, 2 NADH

Every human cell has the capacity to utilize glycolysis for energy production. Which one of the following statements correctly describes an aspect of glycolysis?

Two molecules of ATP are used in the beginning of the pathway

Fructose is the second most common sugar in the human adult diet and its metabolism parallels glycolysis. Which one of the following substances is found in both the fructose metabolic pathway and the glycolytic pathway?

Glyceraldehyde 3-phosphate

A 4-week-old baby has frequent vomiting, enlarged liver, and cataract formation. A urine dipstick test for reducing sugar is positive. The compound detected is most likely which one of the following?

Galactose

Considering the child discussed in the previous question, measurement of which single intracellular metabolite would allow a determination of the enzyme deficiency?

Galactose 1-phosphate

Metformin is used in treating diabetes mellitus type 2. A theoretical concern was lactic acidosis, which in practice does not occur. Which one of the following explains why lactic acidosis does not occur with metformin use?

The heart utilizes lactate as fuel

As glucose has several metabolic routes, which one of the following reactions would commit glucose to following the glycolytic pathway?

Fructose 6-phosphate to fructose 1,6-bisphosphate

Red blood cells require ATP to maintain ion gradients. Red cells generate their energy via which one of the following?

Substrate-level phosphorylation

If 1 mol of lactose is metabolized anaerobically in the liver, how many moles of ATP and NADH will be generated?

4 mol of ATP and 0 mol of NADH

Assume liver PFK-2 is inhibited by a drug that decreases kinase activity while stimulating phosphatase activity. A potential effect of this drug would be which one of the following?

A decreased rate of glycolysis

Rapidly exercising muscle generates lactic acid to directly allow which one of the following reactions to proceed?

Glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate

A type 1 diabetic notices blurred vision. This is caused by which type of reaction within the eye?

A reduction of a sugar

The release of glucagon will lead to the phosphorylation and inactivation of which of the following liver enzyme activities?

PFK-2

An individual displays lactic acidemia, as well as a reduced activity of α-ketoglutarate dehydrogenase activity. The most likely single enzymatic mutation would be in which one of the proteins?

The E3 subunit of pyruvate dehydrogenase

A patient with thiamin deficiency exhibits fatigue and muscle cramps. The muscle cramps are related to an accumulation of which metabolic acid?

Pyruvic acid

Succinate dehydrogenase differs from all other enzymes in the TCA cycle in that it is the only enzyme that displays which characteristic?

It is embedded in the inner mitochondrial membrane.

During exercise, stimulation of the TCA cycle results principally from which one of the following?

Stimulation of the flux through a number of enzymes by a decreased NADH/NAD+ ratio

A deficiency of which compound would lead to an inability to produce coenzyme A?

Pantothenate

One of the major roles of the TCA cycle is to generate reduced cofactors for ATP production. The compound donating the net eight electrons is which one of the following?

Acetyl CoA

Atherosclerosis can narrow the coronary arteries leading to hypoxia of cardiac cells. Which one of the following is likely to occur in the cardiomyocytes during the hypoxic event?

Citrate accumulates

A distance runner allows her muscles to utilize fatty acids as fuel. Which one of the following correctly describes how acetyl CoA is metabolized in the mitochondria?

Substrate-level phosphorylation generates one high-energy phosphate bond during the cycle

A neonate with an X-linked dominant mutation of the α-subunit of E1 in the pyruvate dehydrogenase complex is severely acidotic. Compared with a healthy neonate, what would be the consequence?

An increase in plasma concentrations of lactate and pyruvate

A pyruvate carboxylase deficiency will lead to lactic acidemia due to which one of the following?

An accumulation of NADH in the mitochondrial matrix

Assume that liver pyruvate dehydrogenase kinase exhibited reduced activity. A potential consequence would be which one of the following?

An increased flux of acetyl CoA through the TCA cycle

An elevated NADH/NAD+ ratio in the mitochondria can lead to the allosteric inhibition of which enzyme?

Succinate dehydrogenase

A child has a mitochondrial disorder due to a mutation in the mitochondrial genome that reduces electron flow from NADH. This mutation would directly inhibit which enzyme?

Complex I (NADH dehydrogenase)

Anaplerotic reactions can refill the TCA cycle through which intermediate?

Oxaloacetate

Arsenic can lead to a loss of high-energy phosphate bond formation as catalyzed by which enzyme?

Succinyl-CoA synthetase

Carefully isolated liver mitochondria are incubated with malate. After cyanide is added, which component of the electron transfer chain will be in an oxidized state?

Complex II

Malate is added as an energy source and oxygen consumption increases. Then valinomycin and potassium are added. What is the effect of valinomycin on the proton motive force?

The proton motive force will be decreased, but to a value greater than zero.

Dinitrophenol acts as an uncoupler of oxidative phosphorylation by which mechanism?

Allowing for proton exchange across the inner mitochondrial membrane

A 25-year-old woman with iron-deficiency anemia has fatigue. Such a deficiency would cause fatigue because of which one of the following?

Her decrease in Fe-S centers is impairing the transfer of electrons in the electron transport chain.

Which one of the following would be expected for a patient with an OXPHOS disease?

A high NADH:NAD+ ratio in the mitochondria

A 5-year-old boy with lead poisoning has reduced heme synthesis. Reduced heme synthesis would have little effect on the function of which protein or complex?

Complex I

Rotenone inhibits NADH dehydrogenase. If absorbed by heart mitochondria, what effect would it have on ATP production?

There would be a 95% reduction in ATP production.

Which one of the following is a key component of oxidative phosphorylation?

An ATP synthase to synthesize ATP

Intact mitochondria incubated with high salt lose a component needed for electron flow from pyruvate and oxygen. Which component was lost?

Cytochrome c

UCPs allow oxidation to be uncoupled from phosphorylation. Activation of UCPs as a weight-loss drug could cause which side effect?

Increase in body temperature

In the absence of lactate production, cytoplasmic NADH would accumulate. The electrons on NADH can be transferred to the mitochondrial matrix as a component of which molecule?

Malate (via the malate-aspartate shuttle)

Neurodegenerative diseases can exhibit reduced mitochondrial function due to opening of the MPTP. A key component of this pore catalyzes which reaction?

A cis-prolyl peptide bond to a trans-prolyl peptide bond

The drug atractyloside inhibits the ANT. If mitochondria are incubated with ADP, atractyloside, and pyruvate, and oxygen is added, what would one expect to happen?

A slight, short-term increase in oxygen consumption, followed by no oxygen consumption

A drug inhibits cytoplasmic glycerol 3-phosphate dehydrogenase in a cell line lacking the malate-aspartate shuttle. In the presence of glucose and oxygen, what would increase compared to absence of the drug?

Lactate

Freshly isolated mitochondria are placed with ADP and inorganic phosphate but without oxygen. If dilute HCl is added, what would one expect to observe?

An increase in ATP levels in the mitochondrial matrix

Which one of the following vitamins or enzymes is unable to protect against free-radical damage?

Vitamin B6

Superoxide dismutase is one of the body's primary defense mechanisms against oxidative stress. The enzyme catalyzes which one of the following reactions?

2O2− + 2H+ → H2O2 + O2

The mechanism of vitamin E as an antioxidant is best described by which one of the following?

Vitamin E participates in the reduction of the radicals.

An accumulation of hydrogen peroxide in a cellular compartment can be converted to dangerous radical forms in the presence of which metal?

Iron

The level of oxidative damage to mitochondrial DNA is 10 times greater than that to nuclear DNA. This is due, in part, to which of the following?

Mitochondrial DNA lacks histones.

A patient with chronic granulomatous disease cannot generate primarily which one of the following?

Superoxide

A patient with amyotrophic lateral sclerosis most likely has a mutation leading to the inability to detoxify which one of the following?

Superoxide

Nitroglycerin and erectile dysfunction drugs form nitric oxide (NO). In high concentrations, NO can produce RNOS involved in which disease?

Rheumatoid arthritis

An individual taking xenobiotics such as alcohol and medications can increase free-radical injury through which mechanism?

Induction of enzymes containing cytochrome P450

Which one of the following foods would contain high levels of an antioxidant?

Citrus fruits

The antioxidant glutathione detoxifies hydrogen peroxide via an enzyme that requires which of the following?

Selenium

The regeneration of the protective form of glutathione utilizes an enzyme that requires which of the following?

NADPH

As Parkinson's disease progresses, which one of the following would be expected to be elevated in the man's serum?

Malondialdehyde

A patient treated with a monoamine oxidase inhibitor would directly have which outcome?

Reduces hydrogen peroxide production

The synthesis of nitric oxide radical (NO) requires which of the following?

Arginine