Question

Normal human blood plasma contains all the amino acids required for the synthesis of body proteins, but not in equal concentrations. Alanine and glutamine are present in much higher concentrations than any other amino acids. Suggest why.

Short answer

Alanine and glutamine are present in high concentrations due to their roles in metabolism and nitrogen transport.

Step-by-step solution

Understanding Amino Acid Functions

Alanine and glutamine are amino acids that participate in various crucial functions in the human body, beyond merely being building blocks for proteins.

Alanine's Role in Metabolism

Alanine plays a key role in the glucose-alanine cycle, where it transports nitrogen from muscles to the liver and returns glucose back to the muscles, supporting energy metabolism during fasting or strenuous activity.

Glutamine's Role in Nitrogen Transport

Glutamine is critical for nitrogen metabolism and is involved in transporting ammonia, a byproduct of protein metabolism, to safe disposal or recycling sites in the body.

Demand for Amino Acid Concentrations

The high concentration of alanine and glutamine is due to their significant roles in supporting ongoing metabolic processes, nitrogen transport, and demand in various tissues.

Key concepts

Alanine Function

Alanine is an amino acid that plays a vital role in our body's metabolism. It is not only a building block of proteins but is also crucial for energy production, especially during specific conditions. When you engage in strenuous activity or during periods of fasting, your muscles break down proteins into amino acids. Alanine is one of these amino acids.

This amino acid then enters the bloodstream, traveling to the liver. Once it reaches the liver, it participates in the glucose-alanine cycle. Here, alanine donates its nitrogen, facilitating the production of pyruvate, which the liver converts into glucose. This glucose can then be transported back to the muscles, providing them with a much-needed energy source.

Benefits of alanine in metabolism include:

• Supporting glucose production during fasting.
• Providing muscle energy.
• Assisting in nitrogen transfer.

Glutamine Function

Glutamine is another essential amino acid with significant functions in the body, particularly in nitrogen metabolism. It is the most abundant amino acid in the bloodstream and plays several pivotal roles. One of its primary roles is in the transport of nitrogen.

In protein metabolism, ammonia is produced, which is toxic if it accumulates. Glutamine helps by collecting excess ammonia in tissues and then safely transporting it through the bloodstream to either the liver or kidneys. In these organs, ammonia can be processed and excreted safely.

Functions of glutamine include:

• Transporting ammonia safely in the body.
• Assisting in acid-base balance in the kidneys.
• Supporting the immune system and intestinal health.

Nitrogen Transport

Nitrogen is a fundamental element in amino acids, nucleotides, and other biological compounds. Efficient nitrogen transport is essential for maintaining balance in the body. Both alanine and glutamine play roles in this process.

During protein breakdown, nitrogen is released and must be managed safely to prevent toxicity.

• Alanine helps by carrying nitrogen from muscle tissue to the liver.
• Glutamine carries ammonia, a nitrogenous waste, facilitating its excretion.

This coordinated transport not only helps in detoxifying the body but also ensures nitrogen is available for other pathways, like nucleotide synthesis, crucial for new cell growth.

Glucose-Alanine Cycle

The glucose-alanine cycle is a critical metabolic pathway that underscores the interdependence of muscles and liver, connecting amino acid and glucose metabolism. This cycle is especially pivotal during conditions when energy needs are high, but intake is low, such as fasting or intense exercise.

In this cycle, muscles generate energy by breaking down amino acids, converting them into alanine. Alanine enters the bloodstream, reaching the liver, where it is converted back into pyruvate by deaminating alanine, removing its nitrogen component.

The pyruvate is then used in gluconeogenesis, a process that generates glucose. This glucose is released into the bloodstream and is taken up by muscles. Thus, the cycle begins anew.

• It allows continued muscle function with limited energy intake.
• Ensures nitrogen is safely managed and utilized efficiently.
• Illustrates the elaborate coordination of organ functions in metabolism.