Amino acids are the basic building blocks of proteins. These organic compounds are essential for the body’s structure and function, participating in countless biological processes. Proteins, formed by linking amino acids, are involved in nearly every cellular activity. The human body requires 20 different amino acids, some of which it produces, while others must be obtained through diet.
The Body’s Amino Acid Pool
Unlike fats or carbohydrates, the body does not have specialized storage depots for amino acids. Instead, amino acids exist in a dynamic “amino acid pool” distributed throughout the body’s cells, tissues, and blood. This pool represents a fluctuating collection of free amino acids available for immediate use.
It is continuously replenished through several sources, including the digestion of dietary proteins, which breaks them down into individual amino acids. The ongoing breakdown and recycling of the body’s own proteins, a process known as protein turnover, also contributes to this pool. The synthesis of non-essential amino acids by the body further adds to this circulating supply. This ensures a constant supply of amino acids for various metabolic needs. The free amino acid pool in the blood typically maintains a concentration of approximately 35-65 milligrams per deciliter.
How Amino Acids Are Used
Amino acids from this circulating pool are utilized for various functions. Their primary role involves protein synthesis, crucial for building and repairing tissues like muscles and organs. Amino acids also form enzymes, which catalyze biochemical reactions, and hormones, which act as chemical messengers. They are integral to the production of antibodies that support the immune system.
Beyond protein formation, amino acids contribute to the creation of other vital nitrogen-containing compounds. These include neurotransmitters, which transmit signals in the nervous system, and components of DNA and RNA. When carbohydrate and fat reserves are low, amino acids can also serve as an energy source. Through processes like gluconeogenesis, their carbon skeletons convert into glucose, providing fuel for cells, particularly those in the brain. They can also convert into ketone bodies, offering an alternative energy source during prolonged fasting or starvation.
When Amino Acids Are Not Needed
When the body has excess amino acids beyond its immediate requirements for protein synthesis or other functions, these amino acids cannot be stored. Instead, they undergo deamination, primarily in the liver. During deamination, the nitrogen-containing amino group is removed from the amino acid molecule. This removal forms ammonia, a highly toxic compound.
To prevent ammonia accumulation, the liver swiftly converts it into urea through the urea cycle. Urea is a less toxic compound safely transported in the bloodstream. The kidneys then filter urea from the blood, and it is excreted in urine. The remaining carbon skeletons, after amino group removal, can be utilized for energy production, converted into glucose, or transformed into fatty acids and stored as fat. This mechanism ensures excess amino acids are efficiently processed and eliminated or repurposed, rather than accumulating in the body.