Multiple Choice
In glycolysis (from one molecule of glucose to two molecules of pyruvate), what is the net production of ATP?
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Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway
Glycolysis 1
Multiple Choice
Which steps of glycolysis are considered irreversible under physiological conditions (i.e., have a large negative )?
A
Step 2 (phosphoglucose isomerase), step 5 (triose phosphate isomerase), and step 8 (phosphoglycerate mutase)
B
Step 1 (hexokinase/glucokinase), step 3 (PFK-1), and step 10 (pyruvate kinase)
C
Step 9 (enolase) only
D
Step 4 (aldolase), step 6 (glyceraldehyde-3-phosphate dehydrogenase), and step 7 (phosphoglycerate kinase)
Verified step by step guidance1
Understand that in glycolysis, irreversible steps are those with a large negative Gibbs free energy change (\$\(\Delta\) G\$), making them essentially unidirectional under physiological conditions.
Identify the enzymes catalyzing each step of glycolysis and recall which steps are known to be irreversible: Step 1 (hexokinase/glucokinase), Step 3 (phosphofructokinase-1, PFK-1), and Step 10 (pyruvate kinase).
Recognize that these irreversible steps serve as key regulatory points in glycolysis, controlling the flux through the pathway.
Note that other steps, such as those catalyzed by phosphoglucose isomerase (Step 2), triose phosphate isomerase (Step 5), and phosphoglycerate mutase (Step 8), are reversible because their \$\(\Delta\) G\$ values are close to zero or slightly negative, allowing equilibrium to be reached easily.
Summarize that the irreversible steps are Step 1, Step 3, and Step 10, which correspond to the enzymes hexokinase/glucokinase, PFK-1, and pyruvate kinase, respectively.
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