Question

A man collapses while running a marathon and is taken to the emergency room. His blood is found to be somewhat acidic, and further tests show increased lactate dehydrogenase activity. This enzyme is involved in which of the following pathways? (A) \(\quad\) Anaerobic glycolysis (B) \(\quad \beta\) -Oxidation of fatty acids (C) \(\quad\) Citric acid cycle (D) \(\quad\) Pentose phosphate pathway

Short answer

Lactate dehydrogenase is involved in anaerobic glycolysis.

Step-by-step solution

Identify the Symptoms

The man has collapsed during a marathon and his blood is found to be acidic with increased lactate dehydrogenase activity. This indicates that there is an accumulation of lactate in his blood.

Understanding Lactate Dehydrogenase

Lactate dehydrogenase (LDH) is an enzyme that catalyzes the conversion of pyruvate to lactate when oxygen is low (anaerobic conditions). This is a critical part of anaerobic glycolysis.

Pathway Involvement

Since lactate dehydrogenase is specifically linked with the conversion of pyruvate to lactate under anaerobic conditions, the pathway involved must be anaerobic glycolysis.

Eliminate Other Options

β-Oxidation of fatty acids, the citric acid cycle, and the pentose phosphate pathway do not involve lactate dehydrogenase. These pathways are involved in processes different from those that produce lactate.

Select the Correct Answer

Based on the information provided and the function of lactate dehydrogenase, the enzyme is involved in anaerobic glycolysis.

Key concepts

Anaerobic Glycolysis

Anaerobic glycolysis is a process that occurs when muscles are exerting a lot of energy and oxygen levels are low. This can happen during intense physical activities like running a marathon. In these conditions, the body needs to produce energy quickly. Normally, the body uses aerobic respiration, which occurs in the presence of oxygen and produces a lot of energy. However, when oxygen is scarce, cells switch to anaerobic glycolysis.

This process breaks down glucose into pyruvate, which is then converted into lactate by the enzyme lactate dehydrogenase. This conversion helps to regenerate NAD+, which is necessary for glycolysis to continue. Though anaerobic glycolysis produces less energy compared to aerobic respiration, it allows muscles to keep functioning for a short period under low oxygen conditions.

Lactate Accumulation

During anaerobic glycolysis, the conversion of pyruvate to lactate leads to lactate accumulation in the blood. This build-up happens because the body switches to anaerobic processes to rapidly produce energy in the absence of oxygen. Lactate starts to accumulate when the production rate surpasses the body's ability to clear it.

When lactate accumulates, it can lower blood pH, leading to a condition called acidosis. This condition was observed in the man who collapsed during the marathon. His acidic blood indicated that significant lactate had built up due to extensive anaerobic glycolysis. Understanding lactate accumulation is key in identifying that the pathway involved is anaerobic glycolysis.

Enzyme Activity

Enzymes are biological catalysts that speed up chemical reactions in the body. Lactate dehydrogenase (LDH) is one such enzyme with a vital role in anaerobic glycolysis. LDH catalyzes the conversion of pyruvate to lactate, which is essential when oxygen levels are low. This reaction also regenerates NAD+, a molecule crucial for glycolysis, allowing continuous ATP production even under anaerobic conditions.

Increased LDH activity is particularly noticeable during intense physical activities and can indicate the extent of anaerobic glycolysis happening in the body. For instance, the man in the marathon showed high LDH activity, confirming lactate buildup and supporting the shift to anaerobic glycolysis due to oxygen scarcity.

Pathway Identification

Understanding which metabolic pathway is involved in a particular condition can help identify the cause of symptoms. In our example, identifying that the man has high lactate dehydrogenase activity and acidic blood suggests that anaerobic glycolysis is taking place.

Here is how we can eliminate other pathways:

• β-Oxidation of fatty acids: This process takes place in the mitochondria and primarily deals with breaking down fatty acids, not converting pyruvate to lactate.
• Citric acid cycle: It's also an aerobic process occurring in the mitochondria, unrelated to lactate production.
• Pentose phosphate pathway: This pathway primarily generates NADPH and ribose-5-phosphate, not lactate.

Therefore, by understanding enzyme activity and lactate build-up, we can identify that anaerobic glycolysis is the pathway involved in the man's condition.