Question 1

What is the general name for an enzyme that catalyzes an intramolecular phosphoryl shift?

Accepted Answer

An enzyme that catalyzes an intramolecular phosphoryl shift is called a mutase.

Question 2

The oxidation of 3 mol of glucose by the pentose phosphate pathway may result in the production of:

Accepted Answer

According to the pentose phosphate pathway, for every mol of glucose oxidized, 2 mol of NADPH and 1 mol of pentose are produced. Therefore, for 3 mol of glucose oxidized, we will have 6 mol of NADPH and 3 mol of pentose. Additionally, since the pathway takes place in the cytoplasm, the production of CO₂ (which is a component of the mitochondrial complex I) is not expected, so the correct answer is C.

Question 3

Which statement regarding glycolysis is TRUE?

Accepted Answer

The oxidation reaction in glycolysis, which involves the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, produces two molecules of NADH, which are considered high-energy molecules.

Question 4

Which process does NOT occur in the steps of glycolysis between glyceraldehyde-3-phosphate and phosphoenolpyruvate?

Accepted Answer

A hydration reaction does not occur in the steps of glycolysis between glyceraldehyde-3-phosphate and phosphoenolpyruvate. The steps in that portion of glycolysis include phosphoryl transfer, oxidation, and isomerization, but not hydration.

Question 5

Which enzyme acts in the pentose phosphate pathway?

Accepted Answer

6-phosphogluconate dehydrogenase is the enzyme that acts in the pentose phosphate pathway to convert 6-phosphogluconate to ribulose-5-phosphate, generating NADPH in the process.

Question 6

Which enzyme catalyzes an energy-capture reaction in glycolysis?

Accepted Answer

Glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, which is coupled to the phosphorylation of ADP to ATP. Pyruvate kinase catalyzes the transfer of a phosphate group from phosphoenolpyruvate to ADP, generating ATP.

Question 7

Glucose, labeled with ¹⁴C in different carbon atoms, is added to a crude extract of a tissue rich in the enzymes of the pentose phosphate pathway. The most rapid production of ¹⁴CO₂ will occur when the glucose is labeled in:

Accepted Answer

The pentose phosphate pathway involves the oxidative decarboxylation of glucose-6-phosphate, where the C-1 carbon is released as CO2. Therefore, labeling C-1 with 14C will result in the most rapid production of 14CO2.

Question 8

Which reaction does NOT convert gluconeogenic precursors to the next step in gluconeogenesis?

Accepted Answer

Lactate is converted to pyruvate in the reverse direction of gluconeogenesis by lactate dehydrogenase, which does not lead to the conversion of the precursor to the next step in gluconeogenesis.

Question 9

Which statement about the pentose phosphate pathway is INCORRECT?

Accepted Answer

The pentose phosphate pathway does not require the participation of molecular oxygen. Instead, it is an oxygen-independent pathway that utilizes glucose-6-phosphate to generate NADPH and ribose-5-phosphate.

Question 10

Which statement is TRUE for glycolysis?

Accepted Answer

During glycolysis, a dehydration reaction catalyzed by enolase converts 2-phosphoglycerate to phosphoenolpyruvate, a high-energy molecule.

Question 11

Glucose breakdown in certain mammalian and bacterial cells can occur by mechanisms other than classic glycolysis. In most of these, glucose 6-phosphate is oxidized to 6-phosphogluconate, which is then further metabolized by:

Accepted Answer

The process described is part of the pentose phosphate pathway, where 6-phosphogluconate is decarboxylated to produce ribulose-5-phosphate, a keto-pentose, along with the release of carbon dioxide. This step is crucial for the generation of NADPH and ribose-5-phosphate, which are essential for biosynthetic reactions and nucleotide synthesis, respectively.

Question 12

Which compound(s) is/are a high-energy intermediate(s) in glycolysis?

Accepted Answer

1,3-bisphosphoglycerate and phosphoenol pyruvate are considered high-energy intermediates in glycolysis because they have high phosphoryl-transfer potential, meaning they can readily transfer a phosphate group to ADP to form ATP.

Question 13

Which compound(s) is/are a high-energy product(s) of glycolysis?

Accepted Answer

ATP and NADH are high-energy products of glycolysis, as they contain energy that can be used by the cell for various metabolic processes. Fructose 1,6-bisphosphate, 1,3-bisphosphoglycerate, and phosphoenol pyruvate are intermediates in glycolysis, but they are not considered high-energy products.

Question 14

In some tissues, an increase in insulin will substantially increase the glucose transporters in the cell membrane and the transport of glucose into cells. Which tissues react in this manner?

Accepted Answer

Muscle and adipose tissue are highly responsive to insulin, which promotes the translocation of glucose transporters to the cell membrane, thereby increasing glucose uptake.

Question 15

Which statement is FALSE concerning glycolysis?

Accepted Answer

The statement that glycolysis results in the synthesis of NAD⁺ is false. Glycolysis results in the net synthesis of ATP and the conversion of glucose into pyruvate.

Question 16

Which amount of ATP and NADH identifies net production when 1 mol of DHAP is converted to 1 mol of pyruvate?

Accepted Answer

During the conversion of 1 mol of DHAP to 1 mol of pyruvate, 2 mol of ATP are consumed while 4 mol of ATP are produced (via substrate-level phosphorylation). In addition, 2 mol of NADH are produced through reduction of 2 mol of NAD+ to NADH. Therefore, the net production is 2 mol of ATP and 1 mol of NADH.

Question 17

In a tissue that metabolizes glucose via the pentose phosphate pathway, C-1 of glucose would be expected to end up principally in:

Accepted Answer

The pentose phosphate pathway (PPP) is primarily involved in the production of NADPH and ribose-5-phosphate. During the oxidative phase of the PPP, glucose-6-phosphate is decarboxylated, meaning that the carbon at position 1 of the glucose molecule is released as carbon dioxide. This makes option A correct.

Question 18

The enzyme 2,3-BPG mutase produces 1,3-BPG in red blood cells through an isomerization (rearrangement) reaction. What amino acid(s) would you predict to be important in substrate binding?

Accepted Answer

Lysine (Lys) is a positively charged amino acid, which can interact with the negatively charged phosphate groups of 2,3-BPG, facilitating substrate binding in the enzyme's active site.

Question 19

Which statement is TRUE regarding the glycolytic pathway?

Accepted Answer

The answer of Which statement is TRUE regarding the glycolytic...

Question 20

Why is an anaerobic fate of pyruvate necessary in skeletal muscle?

Accepted Answer

During anaerobic conditions, there is limited availability of NAD⁺, which is necessary for glycolysis to continue. The anaerobic fate of pyruvate, which involves converting it into lactate, allows for the regeneration of NAD⁺ so that glycolysis can continue. Therefore, choice B is the correct answer as it explains the necessity of the anaerobic fate of pyruvate in skeletal muscle.

Quiz 14: Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway