Number of ATPs released at the end of glycolysis from glucose to lactate is?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016

Biochemistry & Nutrition

Medium

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016

Explanation

Anaerobic glycolysis is the metabolic pathway that converts glucose to lactate in the absence of oxygen.
This process involves an initial investment of 2 ATP molecules to activate the glucose molecule.
Subsequently, the pathway generates 4 ATP molecules through substrate-level phosphorylation.
The net gain is calculated as the total ATP produced minus the total ATP consumed (4 - 2 = 2 ATP).
The conversion of pyruvate to lactate regenerates NAD+, allowing glycolysis to continue producing ATP under anaerobic conditions.

Option A: A net gain of one ATP is incorrect. While some steps consume ATP and others produce it, the final balance is not one.
Option C: A net gain of three ATP is incorrect for anaerobic glycolysis starting from glucose. However, if glycolysis starts from glycogen, the net yield is 3 ATP because the initial investment step by hexokinase is bypassed.
Option D: Four ATP represents the gross production of ATP in the payoff phase of glycolysis. It does not account for the two ATP molecules that are consumed in the initial investment phase.

Clinical Relevance

Nursing practice connection: Knowing ATP yield of anaerobic glycolysis helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding the ATP yield of anaerobic glycolysis is crucial for nurses, especially in critical care. Elevated serum lactate is a key biomarker for tissue hypoxia, sepsis, and shock. It signals that cells are relying on this less efficient energy pathway due to insufficient oxygen.
Monitoring lactate levels helps in assessing the severity of illness and the effectiveness of resuscitation efforts. A rising lactate level indicates worsening tissue perfusion, while a falling level suggests improvement.
What if the patient's cells had adequate oxygen? If oxygen were present (aerobic conditions), pyruvate would enter the Krebs cycle and electron transport chain, yielding a much larger amount of ATP (approximately 32 ATP per glucose molecule), and lactate would not be produced in large amounts.

How to Approach the Question

First, identify the key process in the question: 'glycolysis from glucose to lactate'. This specifies anaerobic glycolysis.
Recall the two main phases of glycolysis: the energy investment phase and the energy payoff phase.
Remember the ATP accounting for each phase: 2 ATP are used in the investment phase, and 4 ATP are produced in the payoff phase.
Calculate the net ATP yield by subtracting the ATP consumed from the ATP produced (4 - 2).
Select the option that matches your calculated net yield.
Differentiate this from the gross ATP production (4 ATP) and the ATP yield from aerobic glycolysis (which is much higher).

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) pp. 149-151, 148-150

E6 Biochemistry U Satyanarayana— Part 1 (pp 26-420 of 840) p. 241-243