question

A suspension of yeast cells is being grown under anaerobic conditions such that glucose is degraded to ethanol and carbon dioxide. If one wishes to follow this process by monitoring the release of 14CO2, at which positions in the glucose molecule would the 14C label need to be incorporated?

answer

carbons 3 and 4

question

If an inhibitor of alcohol dehydrogenase is added to the above suspension, the cells rapidly die because

answer

the NAD+ needed to keep glycolysis going is not being recycled so the entire process is shut down and no ATP is produced. Correct. The inability to regenerate NAD+ for the glyceraldehyde-3-phoshate dehydrogenase reaction will bring glycolysis to a halt.

question

When glyceraldehyde-3-phosphate oxidatively converted to 1,3-bisphosphoglycerate in the presence of phosphate and glyceraldehyde-3-phosphate dehydrogenase, what is reduced?

answer

NAD+ Correct. NAD+ is the electron sink for glycolysis. When an intermediate is oxidized, NAD+ is reduced to NADH.

question

The mechanism of glyceraldehyde-3-phosphate dehydrogenase does NOT involve

answer

phosphorylation of the substrate using ATP. Correct. Phosphorylation of the substrate occurs but not at the expense of ATP.

question

Although glucose is the major sugar degraded by the glycolytic pathway, other sugars such as galactose and fructose are also derived from food. These sugars

answer

are metabolized by the glycolytic pathway by conversion to intermediates in the pathway. Correct. Both galactose and fructose enter the glycolytic pathway by conversion to intermediates in the pathway. Fructose is converted to fructose 1-phosphate and then to glyceraldehyde and dihydroxyacetone phosphate. Glyceraldehyde is converted to glyceraldehyde 3-phosphate. Thus, two glycolytic intermediates are produced from fructose. Galactose undergoes four conversions to produce glucose 6-phosphate, a glycolysis intermediate.

question

The three major regulatory enzymes in the glycolytic pathway are

answer

hexokinase, phosphofructokinase, and pyruvate kinase. Correct. These three allosteric enzymes serve key regulatory roles in glycolysis.

question

Well into exercise, the ratio of ATP/AMP in muscle cells decreases. What effect does this ratio reduction have on the activity of phosphofructokinase and pyruvate kinase?

answer

Both enzymes are increased in activity due to lack of allosteric binding of ATP. Correct. If the energy charge falls, glycolysis is stimulated and both phosphofructokinase and pyruvate kinase will increase in activity.

question

The processes of gluconeogenesis and glycolysis are said to be reciprocally regulated. This means that

answer

molecules that inhibit (or activate) one process often have the opposite effect on the other. Correct. The idea behind reciprocal control is that a molecule that affects a degradation pathway will affect a synthetic pathway in an opposite manner.

question

In glycolysis, the isomerization of glucose to fructose is necessary because

answer

it is needed to ensure that equal 3-carbon units can be made. Correct. The creation of equal 3-carbon units allows the same enzymatic machinery to use both of the molecules from glucose after it is split, such that a separate glycolytic pathway is unnecessary.

question

Why might a cancer cell show a preference for glycolysis, even in the presence of oxygen?

answer

Tumor cells can readily form a low oxygen environment as they grow. Correct. Rapid growth of tumor cells often creates hypoxic conditions in the interior of a tumor, favoring tumor cells that utilize glycolysis and can survive under those conditions.

question

In actively contracting skeletal muscle tissue, the major way in which glucose is metabolized is via

answer

lactic acid fermentation. Correct. Because the rate of glycolysis exceeds that of the citric acid cycle, most glucose is converted to lactate in actively contracting muscle tissue.

question

Enzymes that catalyze the same reaction but differ in amino acid sequence are called

answer

isozymes. Correct. The muscle and heart forms of lactate dehydrogenase are examples of isozymes.

question

The process of glycolysis results in the formation of two high-energy phosphate bonds (in the form of ATP). How many high-energy phosphate bonds are consumed during the process of gluconeogenesis using pyruvate as a starting material?

answer

6 Correct. Four ATP and two GTP are needed to produce glucose from pyruvate.

question

What product of contracting muscle tissue is used by the liver as starting material for gluconeogenesis?

answer

lactate Correct. Lactate is transported by the blood stream to the liver where it serves as a starting material for the production of glucose.

question

While glycolysis can occur in most cells, the major site of gluconeogenesis is limited to two tissues. Which of the following is NOT one of them?

answer

muscle Correct. Although lactate from muscle tissue can be used as a starting material for the synthesis of glucose, gluconeogenesis does not occur in muscle tissue.

question

Type 2 diabetes is a disease characterized by overproduction of glucose by the liver and its underutilization by other organs. Which of the following is NOT a cause of diabetes?

answer

the generation of enzymes in the blood that rapidly degrade insulin after release from the pancreas Correct. Neither type of diabetes involves rapid degradation of insulin in the bloodstream.

question

The generation of glucose from glucose 6-phosphate occurs in which membrane-bound organelle(s)?

answer

endoplasmic reticulum

question

Which of the following statements is true of fructose 1,6-bisphosphate but not of fructose 6-phosphate?

answer

It contains two phosphate groups.

question

If both glycolysis and gluconeogenesis were simultaneously operating at the same rate, which of the following statements would be TRUE?

answer

Two ATP and two GTP molecules would be consumed per reaction cycle. AND Hypoglycemia would eventually occur unless food was consumed.

question

Type 2 diabetes is most commonly diagnosed _____ in life and involves _____.

answer

later; insulin resistance

question

If energy levels are low in a cell, the concentration of _____ will be high and _____ will be turned on.

answer

AMP; glycolysis

question

Red blood cells generate all ATP through glycolysis because they lack:

answer

mitochondria

question

Which of the following situations or phrases most accurately describes the citric acid cycle?

answer

"All roads lead to Rome." Correct. In many ways, the citric acid cycle can be considered as the centerpiece of cellular metabolism, with a variety of catabolic and anabolic pathways leading to and from it.

question

In the reaction catalyzed by the pyruvate dehydrogenase complex, the two carbons constituting the acetyl group are

answer

transferred to the lipoamide by an earlier intermediate in the process. Correct. The two carbons are first attached to thiamine pyrophosphate and then transferred to the lipoamide.

question

Which of the following is NOT a product of the reaction catalyzed by pyruvate dehydrogenase complex?

answer

pyruvate Correct.

question

Which of the following is NOT a coenzyme necessary in the function of pyruvate dehydrogenase complex?

answer

ubiquinone Correct.

question

Pyruvate dehydrogenase complex falls within which size range?

answer

4-10 million daltons

question

The core of the pyruvate dehydrogenase complex is made up of eight catalytic _____ that make up the _____ component.

answer

trimers; E2

question

Beriberi is a disease caused by a deficiency of which vitamin?

answer

vitamin B1 (thiamine)

question

Some symptoms of beriberi include:

answer

both muscle weakness and distorted skin sensation.

question

Entry to the citric acid cycle involves the generation of acetyl CoA. The enzyme that catalyzes the production of acetyl CoA is _____. This enzyme is negatively regulated by _____ in a high-energy charge situation.

answer

pyruvate dehydrogenase; NADH

question

The pyruvate dehydrogenase complex is regulated by:

answer

phosphorylation. allosteric interactions. covalent modifications. *All of the above

question

Which enzyme of the citric acid cycle most closely resembles the pyruvate dehydrogenase complex in terms of its structure, organization, and the reaction it performs?

answer

α-ketoglutarate dehydrogenase Correct. The α-ketoglutarate dehydrogenase enzyme is structurally and functionally homologous to the pyruvate dehydrogenase complex.

question

Although the pyruvate dehydrogenase complex is subject to allosteric control, especially inhibition by reaction products, the main regulatory process controlling the enzyme's activity in eukaryotes is

answer

phosphorylation by ATP that turns off the complex and dephosphorylation that turns it on. Correct. High levels of ATP are indicative of a situation in which no further ATP is needed and thus the enzyme is turned off by phosphorylation.

question

In going from acetyl-CoA to succinate, two carbons have entered the cycle and two have been released as CO2. Why is the cycle not considered as complete at this point?

answer

The oxaloacetate used to initiate the cycle must be regenerated. Correct. One must replace what one used to start the cycle (oxaloacetate) in order to keep it going.

question

Assuming that pyruvate was labeled with radioactive 14C in its middle (keto) carbon, where would the radiolabel appear after one turn of the citric acid cycle?

answer

equally divided between the two carboxyl groups of oxaloacetate Correct. The "randomization" of label between the two carboxyl groups results from the reaction catalyzed by fumarase.

question

In the reaction catalyzed by succinyl-CoA synthetase

answer

a succinylphosphate transfers its phosphate to a histidyl residue. Correct. The succinylphosphate generated in the first step of the reaction transfers its phosphate to a histidine in the next step.

question

Of the enzymes of the citric acid cycle, which is not a freely soluble enzyme?

answer

succinate dehydrogenase Correct. Succinate dehydrogenase in associated with the inner mitochondrial membrane with one of its products (FADH2) directly entering the electron transport chain.

question

The purpose of anaplerotic reactions is

answer

to replenish the citric acid cycle if it becomes depleted of intermediates by biosynthetic demands. Correct. One must have some oxaloacetate present in order to start the cycle. If it is depleted, it must be replenished before the cycle can operate.

question

Although the glyoxylate cycle is not present in animals, many plants and animals can use this modified form of the citric acid cycle. The glyoxylate cycle is beneficial in that

answer

it allows the organisms which possess it to grow on acetate. Correct. The ability to use alternate carbon sources provides a metabolic versatility.

question

A person suffering from beriberi (deficiency of vitamin B1) lacks the ability to readily produce

answer

succinyl CoA. Correct. TPP is derived from vitamin B1, and is a necessary cofactor in the α-ketoglutarate dehydrogenase enzyme complex needed to catalyze the production of succinyl CoA.

question

Glucose derived from citric acid cycle molecules must do so via

answer

oxaloacetate. Correct. Oxaloacetate can be shuttled into glucose via the gluconeogenesis pathway.

question

Oxygen is not used at any point in the citric acid cycle. However, the cycle will not work without oxygen because

answer

oxygen is needed to regenerate electron carriers. Correct. In the same way that fermentation regenerates the electron carriers needed for glycolysis, oxygen is needed to serve as the final electron acceptor that will allow a molecule like NADH to return to NAD+.

question

In order for an electron transfer reaction to be energetically spontaneous, which of the following must be TRUE?

answer

The change in reduction potential, ΔEo, must be positive. Correct. A positive value for ΔEo will give a negative value for ΔGo.

question

Which of the following is not a mobile or diffusible electron carrier in the mitochondrial electron transport chain?

answer

FAD Correct. FAD is a component of complex II or succinate dehydrogenase. It feeds electrons directly into the electron transport chain.

question

Of the electron transfer complexes associated with the inner mitochondrial membrane, which is not involved in generation of a proton gradient?

answer

succinate-Q reductase (complex II) Correct. The passage of electrons through complex II does not contribute to the proton gradient.

question

What is the source of electrons at complex II (succinate-Q-reductase)?

answer

FADH2 from the citric acid cycle Correct. FADH2 is generated in the citric acid cycle (in the succinate dehydrogenase-catalyzed conversion of succinate to fumarate) and it enters the electron transport chain at complex II (succinate-Q-reductase).

question

Which of the following describes the direction of proton movement relative to electron transfer and phosphorylation?

answer

Electron transfer pumps protons out of the matrix. As the protons reenter through the ATP synthase, ATP is produced in the matrix. Correct. All directions are correct with respect to both electron transfer and phosphorylation.

question

For a given reduced/oxidized molecular pair (X-/X), a negative reducing potential suggests that the

answer

X has a lower affinity for electrons than H2 does. Correct. The predominance of the reduced hydrogen gas implies that the electron has a higher affinity for the reference standard hydrogen, making the value negative.

question

Consider a substance that can exist in an oxidized form X and a reduced form X-. Such a pair is called a(n):

answer

redox couple

question

Which of the following statements points to the endosymbiotic event yielding intercellular mitochondria?

answer

Mitochondria contain their circular DNA. Mitochondria have a double membrane. Mitochondria contain specific transcription and translation machinery. *All of the above

question

Which of the following proteins involved in the respiratory chain exists as a monomer?

answer

cytochrome c

question

Which of the following may be due to free-radical injury?

answer

emphysema Parkinson disease Duchenne muscular dystrophy *All of the above

question

Which of the following is NOT a part of the Mitchell chemiosmotic hypothesis?

answer

High-energy phosphorylated intermediates that serve as phosphate donors to ADP are generated as a result of electron-transfer reactions. Correct. High energy phosphorylated intermediates are not a part of Mitchell's chemiosmotic hypothesis.

question

Proton flow through the ATP synthase enzyme

answer

results in the release of ATP from its tightly bound state in the active site. Correct. Although readily produced in the active site, ATP is only released when protons flow through the enzyme.

question

The process of glycolysis occurs in the cytoplasm. The electrons from the NADH generated during glycolysis

answer

may enter the electron transport chain either at the level of NADH or FADH2, depending on the shuttle system used to transport them into the mitochondria. Correct. The glycerol-3-phosphate shuttle allows electrons from cytoplasmic NADH to enter the mitochondrial electron transport chain at the level of FADH2 and the malate-aspartate shuttle at the level of NADH.

question

The uncoupler dinitrophenol (DNP) prevents ATP synthesis while allowing electron transport to proceed because

answer

DNP is capable of transporting protons across the membrane, dissipating the proton gradient. Correct. DNP effectively "short circuits" the proton motive force such that it is dissipated before it can be used to drive ATP production.

question

The presence of uncoupling proteins allows _____ energy from the mitochondrial electron transport chain to be used for ATP synthesis and ______ for the production of heat.

answer

less; more Correct. Regulated uncoupling can balance the needs of the organism for ATP and heat.

question

The path taken by electrons to water from NADH generated during the citric acid cycle will NOT pass though

answer

FAD. Correct. FAD is only used for transport of NADH electrons (in some cases) from outside the mitochondria, not ones generated within the mitochondria in the citric acid cycle. NADH from the citric acid cycle also does not pass though the FAD found in Complex II of the electron transport chain.

question

The energy generation of ATP using ATP synthase can be thought of the reverse reaction of what chemical reaction?

answer

ATP hydrolysis and proton movement against a gradient Correct. ATP synthase in reverse involves the favorable ATP hydrolysis that can drive the unfavorable pumping of protons against a gradient.

question

Like other molecular motors, the rotation of a bacterial flagellar apparatus requires a source of energy. What is used to provide energy for this type of molecular motor?

answer

proton gradient across membrane Correct. The proton gradient across the plasma membrane provides the source of energy driving flagellar motion.

question

Peter Mitchell proposed the _____ hypothesis that describes how _____ and _____ are coupled.

answer

chemiosmotic; electron transport; ATP synthesis

question

The regulation of the rate of oxidative phosphorylation by the ADP level is called _____ control.

answer

acceptor

question

Glucose is the most stable hexose because the hydroxyl groups are all in the _____ position.

answer

equatorial *This will be counted wrong, but it is correct. P283 in book. Mentioned to Prof.

question

The key regulatory enzyme for glycolysis is _____.

answer

phosphofructokinase

question

_____ are enzymes that catalyze the transfer of a phosphoryl group from ATP to an acceptor.

answer

Kinases

question

The first irreversible enzymatic reaction unique to a metabolic pathway is called the _____ step.

answer

committed

question

_____ mediate the thermodynamically downhill movement of glucose across plasma membranes.

answer

Glucose transporters

question

What two 3-carbon molecules are generated by the cleavage of fructose-1,6-bisphosphate?

answer

glyceraldehyde-3-phosphate and dihydroxyacetone phosphate

question

What are the primary metabolic fates of pyruvate?

answer

ethanol lactate acetyl CoA *All the above.

question

The process of forming glucose from amino acids is called _____.

answer

gluconeogenesis

question

Some amino acids are converted to glucose via conversion to pyruvate and _____.

answer

oxaloacetate

question

The enzyme that carboxylates pyruvate is _____.

answer

*Didn't get correct. Not sure.

question

ATP in the reaction catalyzed by PEPCK is use to fix _____ to biotin

answer

carbon dioxide

question

The first step in gluconeogenesis is the _____ of pyruvate to form oxaloacetate.

answer

carboxylation

question

E1 of the pyruvate dehydrogenase complex requires the coenzyme _____ for proper activity.

answer

Answer should be TPP but not accepted.

question

High-energy charge, which results in increasing concentration of NADH, _____ the activity of PDH.

answer

inhibits

question

The citric acid cycle is also known as the:

answer

Krebs cycle and the tricarboxylic acid cycle.

question

Pyruvate is decarboxylated by which subunit of the PDH?

answer

E1

question

What are the steps involved (in order) in the conversion of pyruvate to acetyl CoA?

answer

decarboxylation, oxidation, transfer to CoA

question

Pyruvate dehydrogenase is _____ when ATP/ADP ratios are high.

answer

inhibited

question

Carbons from carbohydrate enter the citric acid cycle in the form of _____.

answer

acetyl CoA

question

In the citric acid cycle, the _____ is produced by a substrate-level phosphorylation.

answer

GTP *CAREFUL! This is tricky. In glycolysis it is ATP!

question

In general, the citric acid cycle is inhibited under _____ (high, low) energy conditions.

answer

high

question

What molecule initiates the citric acid cycle by reacting with oxaloacetate?

answer

acetyl CoA

question

The direct movement of substrates from one enzyme to the next is called:

answer

substrate channeling.

question

Formation of citrate from acetyl CoA and oxaloacetate is a(n) _____ reaction.

answer

condensation

question

A strong oxidizing agent has a tendency to _____ (accept, donate) electrons.

answer

accept

question

Another name for coenzyme Q is _____.

answer

ubiquinone

question

ytochrome _____ is the only water-soluble cytochrome of the electron-transport chain.

answer

c

question

The transfer of a single electron to O2 forms the reactive _____ ion.

answer

superoxide

question

_____ is an enzyme that scavenges H2O2 and converts it to molecular oxygen and water.

answer

Catalase

question

_____ are the result of uncontrolled electron transfer to oxygen.

answer

Oxygen radicals

question

Electron flow down the electron-transport chain leads to the:

answer

transport of protons across the inner mitochondrial membrane from inside the matrix to the intermembrane space.

question

Which of the following does NOT pump protons? Complex I Complex II Complex III Complex IV

answer

Complex II

question

What is a cytochrome?

answer

a protein that transfers electrons, and that also contains a heme prosthetic group

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