Glucose Metabolism Review

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Questions and Answers

During glycolysis, what is the net yield of ATP and NADH per molecule of glucose that is fully processed?

2 ATP, 4 NADH
4 ATP, 4 NADH
4 ATP, 2 NADH
2 ATP, 2 NADH (correct)

Which statement accurately describes the location of glycolysis and the citric acid cycle within a eukaryotic cell?

Both glycolysis and the citric acid cycle occur in the cytoplasm.
Both glycolysis and the citric acid cycle occur in the mitochondrial matrix.
Glycolysis occurs in the cytoplasm, while the citric acid cycle takes place in the mitochondrial matrix. (correct)
Glycolysis occurs in the mitochondrial matrix, while the citric acid cycle takes place in the cytoplasm.

Why is the reaction catalyzed by the pyruvate dehydrogenase complex considered an important control point in metabolism?

It irreversibly links glycolysis to the citric acid cycle and regulates the entry of pyruvate into the mitochondria. (correct)
It determines the rate of oxidative phosphorylation by directly affecting ATP synthase activity.
It controls the rate of fatty acid synthesis by regulating acetyl-CoA transport.
It directly regulates the rate of glycolysis under anaerobic conditions.

Coenzyme A (CoA) is crucial to the citric acid cycle because it functions to:

transfer functional groups from one molecule to another. (D) Signup and view all the answers

How do lipoyllysine, thiamine pyrophosphate (TPP), and FAD contribute to the activity of the pyruvate dehydrogenase complex?

They serve as prosthetic groups that remain tightly bound to the enzyme and participate directly in the catalytic mechanism. (B) Signup and view all the answers

What is the primary role of thiamine pyrophosphate (TPP) in the pyruvate dehydrogenase complex?

To stabilize a carbanion intermediate during decarboxylation. (C) Signup and view all the answers

A researcher mutates a bacterial strain such that lipoic acid can no longer be attached to the bacterial pyruvate dehydrogenase complex. What outcome do you expect?

The PDC would be unable to transfer acyl groups, halting the conversion of pyruvate to acetyl-CoA. (D) Signup and view all the answers

Which of the following best describes the mobile arm of E2 (dihydrolipoyl transacetylase) in the pyruvate dehydrogenase complex?

It ensures the transfer of the reaction intermediate between active sites within the complex. (B) Signup and view all the answers

What direct molecular change occurs during the reaction catalyzed by citrate synthase in the citric acid cycle?

The methyl group of acetyl-CoA is converted to a methylene group in citrate. (B) Signup and view all the answers

To initiate catalysis within citrate synthase, which substrate binds first and what conformational change does this induce?

Oxaloacetate binds first, inducing an open form of the enzyme that can accommodate acetyl-CoA. (C) Signup and view all the answers

What is the role of the iron-sulfur center in the aconitase enzyme during the citric acid cycle?

It stabilizes the negatively charged transition state during isomerization. (C) Signup and view all the answers

How does the isocitrate dehydrogenase enzyme contribute to the regulation of the citric acid cycle?

It is inhibited by ATP and NADH, and activated by ADP, modulating the cycle's activity based on the cellular energy charge. (A) Signup and view all the answers

Which enzymatic reaction in the citric acid cycle is most similar to the reaction catalyzed by the pyruvate dehydrogenase complex?

The $\alpha$-ketoglutarate dehydrogenase complex reaction. (C) Signup and view all the answers

During the conversion of succinyl-CoA to succinate, what type of reaction occurs, and what molecule is generated?

Substrate-level phosphorylation; GTP (C) Signup and view all the answers

What is the significance of succinate dehydrogenase being bound to the inner mitochondrial membrane, unlike other citric acid cycle enzymes?

It allows for the direct transfer of electrons from FADH2 to the electron transport chain. (C) Signup and view all the answers

Why is the free energy change ($\Delta G'$) for the malate dehydrogenase reaction highly positive, yet the citric acid cycle proceeds efficiently under cellular conditions?

The subsequent highly exergonic citrate synthase reaction lowers the concentration of oxaloacetate, pulling the malate dehydrogenase reaction forward. (B) Signup and view all the answers

What is meant by the statement that 'the citric acid cycle functions overall as a catalyst'?

The cycle regenerates oxaloacetate, which is essential for the entry of acetyl-CoA, allowing continuous oxidation of acetyl units without net consumption of cycle intermediates. (C) Signup and view all the answers

What is the net result of one turn of the citric acid cycle?

Two molecules of CO2, one GTP, three NADH, and one FADH2 are produced, with oxaloacetate regenerated. (B) Signup and view all the answers

Which best describes how the energy captured by electron transfer leads to the production of NADH and FADH2 during the citric acid cycle?

Electrons from fuel molecules are transferred to NAD+ and FAD through redox reactions. (B) Signup and view all the answers

Which of the following is an accurate statement regarding the regulatory mechanisms of the citric acid cycle?

$\alpha$-ketoglutarate dehydrogenase is competitively inhibited by succinyl-CoA. (B) Signup and view all the answers

How does ATP impact the regulation of pyruvate dehydrogenase?

ATP activates a kinase that phosphorylates and inactivates the E1 subunit of the complex. (C) Signup and view all the answers

Under what cellular conditions would you expect the citric acid cycle to be down-regulated?

High ATP, High NADH (D) Signup and view all the answers

Which of the following enzymes is directly regulated by calcium ions ($Ca^{2+}$) in certain cell types?

$\alpha$-Ketoglutarate Dehydrogenase Complex (B) Signup and view all the answers

What is the purpose of anaplerotic reactions related to the citric acid cycle?

To replenish the pool of citric acid cycle intermediates that have been drained for biosynthetic purposes. (B) Signup and view all the answers

What is the role of biotin in the pyruvate carboxylase reaction, and how does this relate to the larger metabolic landscape?

Biotin acts as a flexible arm to carry activated carbon dioxide, linking bicarbonate activation with pyruvate carboxylation. (A) Signup and view all the answers

Pyruvate carboxylase is an important enyzme in both gluconeogenesis and the citric acid cycle. What is the most important allosteric regulator of this enzyme?

Acetyl-CoA (C) Signup and view all the answers

If a researcher discovers a new metabolic disease characterized by the build-up of succinate, and wants to treat this disease through dietary restriction, what would their recommendation be?

Dietary restricition of anaplerotic pathways. (C) Signup and view all the answers

In the context of the citric acid cycle and cellular metabolism, what is meant by the term 'biological tethers'?

Flexible molecules that allow enzyme prosthetic groups to reach multiple active sites. (C) Signup and view all the answers

How many ATP molecules can be generated from one molecule of succinate through citric acid cycle oxidation?

16.5 ATP molecules (D) Signup and view all the answers

Assuming that one mole of NADH is energetically equivalent to 2.5 moles of ATP and one mole of FADH2 is equivalent to 1.5 moles of ATP, arrange the following compounds based on their energy generating potential, from highest to lowest:

NADH, FADH2 (C) Signup and view all the answers

During gluconeogenesis, which enzyme is responsible for converting oxaloacetate to phosphenolpyruvate (PEP)?

PEP carboxykinase. (D) Signup and view all the answers

If a genetic defect prevents a cell from producing a functional malic enzyme, what direct consequence would you expect to observe regarding the interplay between cellular respiration and gluconeogenesis?

Fewer quantities of malate will be converted to pyruvate. (C) Signup and view all the answers

What structural feature of biotin makes it ideally suited for its role in carboxylation reactions within metabolic pathways?

Biotin has a nucleophile nitrogen that captures carbon dioxide. (B) Signup and view all the answers

Biotin is necessary for several metabolic processes. Which statement accurately describes how Biotin aids in the activity of pyruvate carboxylase?

Biotin acts as a flexible arm to carry activated carbon dioxide. It links the activation of bicarbonate to pyruvate carboxylate. (B) Signup and view all the answers

Which of the enzymes listed requires both ATP and Biotin?

Pyruvate carboxylase (D) Signup and view all the answers

During the first step of the pyruvate carboxylase reaction, biotin becomes?

Carboxylated. (C) Signup and view all the answers

What metabolic derangement would most likely result from a vitamin B7 (biotin) deficiency?

Inhibition of fatty acid biosynthesis and accumulation of pyruvate. (C) Signup and view all the answers

Malate, oxaloacetate, and citrate are considered intermediates of the citric acid cycle. In what way are they used during the anabolic process?

They may act as direct precursors for the biosynthesis of fatty acids, sterols, or particular amino acids and bases. (A) Signup and view all the answers

Which process does NOT act to form oxaloacetate?

Acetyl-CoA (D) Signup and view all the answers

How does high ATP affect the regulation of citrate synthase?

ATP inhibits citrate synthase activity by acting at allosteric sites. (D) Signup and view all the answers

Isocitrate dehydrogenase is considered ATP for the Citric Acid cycle. How would high levels of ATP in the cell act on Isocitrate dehydrogenase?

Inhibits the activity. (A) Signup and view all the answers

Considering the irreversible nature of the pyruvate dehydrogenase complex reaction, under what conditions would the cell most likely rely on alternative pathways to generate acetyl-CoA?

When the cell has a high ATP/ADP ratio and requires more anabolic precursors. (B) Signup and view all the answers

If a researcher introduced a non-hydrolyzable analog of acetyl-CoA into a cell undergoing the citric acid cycle, what immediate effect would you expect to observe?

Inhibition of citrate synthase, leading to a buildup of oxaloacetate. (C) Signup and view all the answers

In a scenario where a cell's mitochondrial membrane is compromised, leading to a loss of the proton gradient, how would the activity of the citric acid cycle be affected, and why?

The cycle would slow down as the regeneration of NAD+ and FAD from NADH and FADH2 is impaired. (D) Signup and view all the answers

What would be the immediate impact on the citric acid cycle if a mutation caused aconitase to bind citrate more tightly but release isocitrate less efficiently?

Buildup of citrate, leading to feedback inhibition of glycolysis. (D) Signup and view all the answers

If a researcher discovers a novel compound that selectively inhibits the carboxybiotinyl-enzyme intermediate formation in pyruvate carboxylase, what impact would this have on gluconeogenesis and the citric acid cycle?

Both gluconeogenesis and the citric acid cycle would be inhibited. (B) Signup and view all the answers

Considering that succinate dehydrogenase is directly involved in the electron transport chain, what would be the immediate consequence of a genetic mutation that impairs its ability to bind FAD?

Decreased levels of fumarate and reduced electron transfer to ubiquinone. (B) Signup and view all the answers

Under conditions of extreme starvation, the body begins to break down muscle protein to provide carbon skeletons for energy production. How would the influx of amino acids affect the citric acid cycle, and what compensatory mechanisms would be activated?

The citric acid cycle would initially increase activity but then be sustained by anaplerotic reactions. (B) Signup and view all the answers

If a cell were engineered to express a mutated malate dehydrogenase with a significantly lower affinity for NAD+, how would this alteration impact both the citric acid cycle and gluconeogenesis?

Both the citric acid cycle and gluconeogenesis would be inhibited due to decreased oxaloacetate production. (C) Signup and view all the answers

Suppose a researcher introduces a synthetic molecule that effectively inhibits the movement of the E2 subunit's lipoyllysine arm within the pyruvate dehydrogenase complex. What direct effect would this have on the complex's function?

Preventing the transfer of the acetyl group to CoA by E2. (A) Signup and view all the answers

How does the presence of 'biological tethers,' such as lipoyllysine in the pyruvate dehydrogenase complex, contribute to the overall efficiency of metabolic pathways, and what would be the most likely consequence of their absence?

They facilitate substrate channeling between active sites, decreasing the transit time, with their absence likely decreasing the overall reaction rate. (D) Signup and view all the answers

Flashcards

What is glycolysis?

A pathway made up of 10 enzyme-catalyzed steps where glucose is transformed into 2 molecules of pyruvate.

What is an anaerobic process?

Does not require O2.

What is Phase I of glycolysis?

5 steps where glucose is phosphorylated and split into 2 triose phosphates, costing 2 ATP.

What is Phase II of glycolysis?

5 steps of oxidation and phosphorylation that yields 2 NADH + 4 ATP, resulting in a net yield of ATP = 2; NADH = 2