Q: Which of the following best describes the net reaction of glycolysis?

$$\text{Glucose} + 2\ \text{NAD}^+ + 2\ \text{ADP} + 2\ \text{P}_i \rightarrow 2\ \text{Pyruvate} + 2\ \text{NADH} + 2\ \text{ATP} + 2\ \text{H}_2\text{O} + 2\ \text{H}^+$$

Question 1

Which of the following statements best explains why aerobic glycolysis yields more energy than anaerobic glycolysis?

Accepted Answer

Aerobic glycolysis allows the complete oxidation of glucose to CO$$_2$$ and H$$_2O$$, utilizing the electron transport chain for additional ATP production.

Question 2

During vigorous exercise, muscle cells switch to lactic acid fermentation. What is the primary biochemical reason for this switch?

Accepted Answer

To regenerate NAD$$^+$$ from NADH, allowing glycolysis to continue producing ATP under hypoxic conditions.

Question 3

Which enzyme catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate in glycolysis, and what is the significance of this step?

Accepted Answer

Pyruvate kinase; it is a highly exergonic, irreversible step that generates ATP.

Question 4

A patient with galactosemia is unable to convert galactose to glucose. Which metabolic pathway is directly affected by this defect?

Accepted Answer

Entry of galactose into glycolysis, leading to impaired energy production from dietary galactose.

Question 5

Which of the following best describes the net reaction of glycolysis?

Accepted Answer

$$	ext{Glucose} + 2\ 	ext{NAD}^+ + 2\ 	ext{ADP} + 2\ 	ext{P}_i ightarrow 2\ 	ext{Pyruvate} + 2\ 	ext{NADH} + 2\ 	ext{ATP} + 2\ 	ext{H}_2	ext{O} + 2\ 	ext{H}^+$$

Question 6

Which of the following steps in gluconeogenesis bypasses an irreversible step in glycolysis?

Accepted Answer

Conversion of fructose-1,6-bisphosphate to fructose-6-phosphate by fructose-1,6-bisphosphatase.

Question 7

Which of the following is NOT a fate of pyruvate in cells?

Accepted Answer

Conversion to glucose via the pentose phosphate pathway.

Question 8

Which cofactor is required for the decarboxylation of pyruvate to acetaldehyde during ethanol fermentation, and what vitamin is it derived from?

Accepted Answer

Thiamine pyrophosphate (TPP), derived from vitamin B$$_1.$$

Question 9

Which of the following statements about the preparatory phase of glycolysis is correct?

Accepted Answer

It consumes 2 ATP molecules to phosphorylate glucose and fructose-6-phosphate.

Question 10

A person with lactose intolerance lacks which enzyme, and what is the physiological consequence in the intestine?

Accepted Answer

Lactase; undigested lactose causes osmotic imbalance, leading to water retention and diarrhea.

Question 11

Which of the following best explains why fats are not considered glucogenic in mammals?

Accepted Answer

Fatty acid catabolism does not produce intermediates that can enter the gluconeogenic pathway.

Question 12

Which enzyme catalyzes the first committed step of glycolysis, and why is this step considered committed?

Accepted Answer

Phosphofructokinase-1; it commits glucose to glycolysis by converting fructose-6-phosphate to fructose-1,6-bisphosphate.

Question 13

Which of the following is a key difference between glycolysis and gluconeogenesis?

Accepted Answer

Gluconeogenesis bypasses the irreversible steps of glycolysis using different enzymes.

Question 14

Which of the following best describes the role of the pentose phosphate pathway in cellular metabolism?

Accepted Answer

It generates pentose sugars and NADPH from glucose-6-phosphate.

Question 15

Which of the following reactions in glycolysis is coupled to the reduction of NAD$$^+ to $$NADH?

Accepted Answer

Oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.

Question 16

Which of the following is a direct product of the enzyme aldolase in glycolysis?

Accepted Answer

Glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

Question 17

Which of the following statements about the fate of NADH produced in glycolysis is correct?

Accepted Answer

Under aerobic conditions, NADH is transported to mitochondria for ATP production via the electron transport chain.

Question 18

Which enzyme is responsible for the hydrolysis of glucose-6-phosphate to free glucose in gluconeogenesis, and where does this reaction occur?

Accepted Answer

Glucose-6-phosphatase; endoplasmic reticulum.

Glycolysis and Gluconeogenesis: Pathways of Glucose Metabolism

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