Question

Which of the following is not produced by an animal muscle cell operating under anaerobic conditions? a. heat b. pyruvate c. PGAL d. ATP e. lactate f. oxygen

Short answer

Oxygen is not produced by an animal muscle cell under anaerobic conditions.

Step-by-step solution

Identify the Products of Anaerobic Conditions

Under anaerobic conditions, animal muscle cells perform glycolysis and convert glucose to energy. The primary products include lactate, ATP, pyruvate (which can be further reduced to lactate), PGAL (glyceraldehyde-3-phosphate as an intermediate in glycolysis), and heat. Oxygen is not produced as it is absent in anaerobic conditions.

Analyze Each Option

Let's analyze each option with respect to muscle cells under anaerobic conditions: - **a. heat:** Heat is produced as a byproduct of metabolic processes. - **b. pyruvate:** Pyruvate is produced during glycolysis. - **c. PGAL:** PGAL is an intermediate in glycolysis. - **d. ATP:** ATP is generated during glycolysis. - **e. lactate:** Lactate is produced from pyruvate in the absence of oxygen. - **f. oxygen:** Oxygen is not produced in anaerobic processes.

Conclusion

Based on the analysis, option **f. oxygen** is the only substance not produced by an animal muscle cell operating under anaerobic conditions. All other options are either direct products or intermediates in the process.

Key concepts

Glycolysis

Glycolysis is the initial step of both aerobic and anaerobic respiration. It occurs in the cytoplasm of the cell and involves the breakdown of glucose into pyruvate. This process does not require oxygen, making it essential for energy production under anaerobic conditions. During glycolysis, one molecule of glucose is converted into two molecules of pyruvate.

• This conversion process involves a series of ten enzyme-catalyzed reactions.
• Each step in glycolysis is specifically coordinated to harvest as much energy as possible.
• The net energy yield from glycolysis is two molecules of ATP and two molecules of NADH.

These ATP molecules are crucial as they provide the energy required for various cellular processes, especially when oxygen is scarce.
The pyruvate produced can then be used in other metabolic pathways, such as lactate fermentation, in the absence of oxygen.

Animal Muscle Cell

Animal muscle cells are specifically adept at functioning in both aerobic and anaerobic conditions. Muscle cells, known as myocytes, must be able to quickly adapt to the body's energy requirements. During intense physical activity:

• Oxygen supply to muscle cells may become limited.
• Muscle cells rely on anaerobic respiration for energy.
• This ensures that ATP is rapidly produced to meet immediate energy demands.

The absence of sufficient oxygen shifts muscle cells to rely on glycolysis followed by lactate fermentation. This system efficiently compensates for the quick bursts of energy required during strenuous exercise.
Understanding the adaptive response of muscle cells is essential in recognizing how the body meets energy demands without oxygen, especially during high-intensity workouts.

ATP Production

ATP, or adenosine triphosphate, is the primary energy currency of the cell. It powers various biological processes by providing a quick and easy source of energy. In the context of anaerobic respiration inside muscle cells:

• ATP is produced during glycolysis.
• This process yields two molecules of ATP per glucose molecule.
• Without oxygen, the cells cannot utilize the more efficient aerobic respiration pathway.

Even though ATP production via anaerobic processes is less efficient than aerobic pathways, it is fast and sufficient for short-term energy needs.
This is why activities that demand quick energy bursts rely heavily on anaerobic respiration.

Lactate Fermentation

Lactate fermentation is a crucial anaerobic process that takes place in muscle cells when oxygen levels are low. This process converts pyruvate, a glycolysis product, into lactate. The key steps involve:

• Oxidation of NADH to NAD⁺, which is crucial for allowing glycolysis to continue.
• The reduction of pyruvate to lactate, facilitated by the enzyme lactate dehydrogenase.

Lactate can accumulate in the muscles, causing the temporary discomfort known as "muscle burn." However, this process allows glycolysis to continue by regenerating NAD⁺ from NADH.
This regeneration is essential because it prevents the depletion of NAD⁺, ensuring continuous ATP production in the absence of oxygen.
Lactate may later be converted back to pyruvate or undergo further metabolism in the liver through the Cori cycle.