Question 1

Which enzyme catalyzes bicarbonate "activation" by attachment to the g-phosphate of ATP to form carbonyl phosphate?

Accepted Answer

Pyruvate carboxylase catalyzes the reaction in which bicarbonate is "activated" by attachment to the g-phosphate of ATP to form carbonyl phosphate.

Question 2

Which of the following is absolutely essential for the activation of pyruvate carboxylase?

Accepted Answer

Pyruvate carboxylase is activated by high concentrations of acetyl-CoA, which serves as a signal of high energy status and the need for more oxaloacetate to feed into the TCA cycle for energy production.

Question 3

Which of the following enzymes is NOT unique to gluconeogenesis?

Accepted Answer

Phosphoglucoisomerase is an enzyme involved in the glycolysis pathway and is not unique to gluconeogenesis. Glucose-6-phosphatase, fructose-1,6-bisphosphatase, and PEP carboxykinase are all enzymes that are unique to gluconeogenesis.

Question 4

In the Cori cycle,the liver shares the load of exercising muscle.What is this a result of?

Accepted Answer

The Cori cycle involves the conversion of lactate produced by exercising muscle to glucose in the liver, which is then released back into the bloodstream and taken up by muscle for energy production. This process requires the oxidation of NADH to NAD+ in the liver, which can only occur if there is a high NAD+/NADH ratio. Therefore, choice C is the best answer. High acetate levels (choice A) and high galactose levels (choice B) are not directly relevant to the Cori cycle, and a high FAD/FADH ratio (choice D) is not necessary for this process.

Question 5

The pentose phosphate pathway is an important source of NADPH and for ribose-5-phosphate.Which of the following is NOT made from ribose-5-phosphate?

Accepted Answer

Ribose-5-phosphate is a precursor for the synthesis of nucleotides and nucleic acids, not for fatty acids. Fatty acid synthesis primarily involves acetyl-CoA as a precursor and utilizes NADPH, which can be produced by the pentose phosphate pathway, but ribose-5-phosphate itself is not directly used in fatty acid synthesis.

Question 6

What is the endoplasmic reticulum-bound enzyme that hydrolyzes glucose-6-phosphate to glucose in liver?

Accepted Answer

Glucose-6-phosphatase is the endoplasmic reticulum-bound enzyme that hydrolyzes glucose-6-phosphate to glucose in liver. Glucose oxidase oxidizes glucose to gluconic acid in certain bacteria and fungi. Hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate. Phosphoglucomutase is an enzyme that converts glucose-6-phosphate to glucose-1-phosphate.

Question 7

How many ATP and GTP combined are required in gluconeogenesis for 2 pyruvate glucose?

Accepted Answer

For each molecule of pyruvate converted to glucose, 4 ATP and 2 GTP are required. Therefore, for 2 pyruvate molecules, 8 ATP and 4 GTP are required, which when combined total up to 12 nucleotides. However, during the process of gluconeogenesis, 2 ATP molecules are actually generated, so the net requirement for ATP and GTP is only 6. Therefore, the correct answer is C) 6.

Question 8

Glucose monitoring devices use the reaction,glucose + O₂ + 2 H₂O → gluconate + 2 H₂O₂.Which enzyme catalyzes this reaction?

Accepted Answer

Glucose oxidase catalyzes the reaction of glucose with oxygen to produce gluconate and hydrogen peroxide.

Question 9

What is the primary regulatory point of gluconeogenesis?

Accepted Answer

The primary regulatory point of gluconeogenesis is fructose-1,6-bisphosphatase, which catalyzes the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate, a key step in reversing glycolysis and allowing for the synthesis of glucose.

Question 10

Which conditions trigger the conversion of pyruvate into OAA for gluconeogenesis?

Accepted Answer

High levels of ATP and acetyl CoA indicate that the cell has a high energy state and sufficient building blocks for fatty acid synthesis, respectively. This environment promotes the conversion of pyruvate into oxaloacetate (OAA) for gluconeogenesis, as the cell is not in need of immediate energy from glycolysis but rather is preparing to store energy as glucose or glycogen for future use.

Question 11

What is synthesized in gluconeogenesis?

Accepted Answer

Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate precursors, such as lactate, glycerol, and amino acids. This is important for maintaining blood glucose levels during fasting or during periods of high energy demand.

Question 12

Which enzyme of gluconeogenesis is NOT found in the cytosol?

Accepted Answer

Pyruvate carboxylase is the only enzyme of gluconeogenesis that is found in the mitochondria, whereas PEP carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase are found in the cytosol.

Question 13

Which of these reactions represents the gluconeogenic reversal of PFK-1 in glycolysis?

Accepted Answer

The gluconeogenic reversal of PFK-1 in glycolysis involves the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate. Choice D represents this reaction, with the addition of water (H₂O) leading to the separation of the phosphate group, forming fructose-6-phosphate and inorganic phosphate (Pi). Choices A, B, and C do not represent the reversal of PFK-1 in glycolysis.

Question 14

Which of these steps is NOT a component of the pyruvate carboxylase-catalyzed reaction?

Accepted Answer

The pyruvate carboxylase-catalyzed reaction involves the following steps: (1) Binding of biotin to pyruvate carboxylase, (2) Formation of N-carbonyl biotin from biotin, ATP, and HCO3-, (3) Formation of carbonyl phosphate from N-carbonyl biotin and ATP, (4) Formation of oxaloacetate from C-3 carbanion of pyruvate attacking N-carbonyl biotin. There is no attack of H₂CO3 on ATP involved in this reaction.

Question 15

Which of the following is NOT a substrate for gluconeogenesis?

Accepted Answer

Acetate cannot be used as a substrate for gluconeogenesis, as it acts as an inhibitor of this process by promoting lipid synthesis instead. Glycerol, lactate, and pyruvate can all be converted to glucose via gluconeogenesis.

Question 16

Which 3 enzyme-regulated reactions of glycolysis are replaced by alternative reactions in the gluconeogenic pathway?

Accepted Answer

The three enzyme-regulated reactions of glycolysis that are replaced by alternative reactions in the gluconeogenic pathway are glucokinase, PFK-1, and pyruvate kinase. In the gluconeogenic pathway, glucose-6-phosphatase replaces glucokinase, fructose-1,6-bisphosphatase replaces PFK-1, and phosphoenolpyruvate carboxykinase (PEPCK) replaces pyruvate kinase. These alternative reactions are necessary to bypass the irreversible steps in glycolysis and allow the synthesis of glucose from non-carbohydrate precursors.

Question 17

Which of the following is NOT required for pyruvate carboxylase?

Accepted Answer

Thiamine pyrophosphate (TPP) is not required for pyruvate carboxylase; it is a cofactor for other enzymes like pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. Pyruvate carboxylase requires biotin, acetyl-CoA as an allosteric activator, and is a tetrameric enzyme found in the mitochondria.

Question 18

Which major tissues carry out gluconeogenesis?

Accepted Answer

The liver and kidneys are the major tissues that carry out gluconeogenesis. The liver is the primary site of gluconeogenesis and is responsible for making glucose from non-carbohydrate sources. The kidneys can also contribute to gluconeogenesis, particularly during times of prolonged fasting or starvation. The brain and muscles do not carry out significant amounts of gluconeogenesis. While red blood cells do not have mitochondria and therefore cannot make glucose via gluconeogenesis, they can still utilize glucose as a source of energy.

Question 19

Which molecule does pyruvate carboxylase consume in order to drive a carboxylation so that PEP carboxykinase could use the energy from decarboxylation to facilitate formation of PEP?

Accepted Answer

Pyruvate carboxylase consumes ATP to add a carboxyl group to pyruvate, forming oxaloacetate. This process is an anaplerotic reaction, replenishing the citric acid cycle intermediates. ATP provides the necessary energy for this carboxylation reaction.

Question 20

Glucose-6-phosphatase is located in the endoplasmic reticulum.What does the enzyme produce in vesicles that diffuse to the plasma membrane,releasing their contents into the blood stream?

Accepted Answer

Glucose-6-phosphatase produces glucose that is released into the blood stream.

Quiz 21: Gluconeogenesis, glycogen Metabolism, and the Pentose Phosphate Pathway