Amino Acids: The Building Blocks of Proteins

Amino acids are the building blocks of proteins. Proteins are essential for the structure and function of all cells and tissues in the body. There are 20 common amino acids that combine to form protein chains. Of these 20 amino acids, nine are considered essential amino acids that the body cannot produce on its own. Getting adequate amounts of essential amino acids from your diet is crucial for good health.

What are Amino Acids?

Amino acids are organic compounds that contain an amino group (-NH2) and a carboxyl group (-COOH). The key elements found in amino acids are carbon, hydrogen, oxygen, and nitrogen.

There are over 500 naturally occurring amino acids, but only 20 amino acids are encoded by the universal genetic code. These 20 amino acids are known as standard or common amino acids. They form short polymer chains called peptides or longer chains called proteins.

Structure of Amino Acids

In addition to an amino group and carboxyl group, each amino acid has a unique side chain or R group that gives it distinct chemical properties. This R group helps determine the interaction of different amino acids to form protein structures.

Based on the properties of their R groups, amino acids can be classified as:

• Nonpolar/Hydrophobic e.g. alanine, valine
• Polar/Hydrophilic e.g. serine, threonine
• Positively Charged e.g. lysine, arginine
• Negatively Charged e.g. aspartic acid, glutamic acid

Essential and Nonessential Amino Acids

Of the 20 common α-amino acids, nine are considered essential amino acids for humans because the body cannot produce them and they must be obtained from food sources. The nine indispensable amino acids are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine.

The remaining 11 amino acids are nonessential, meaning they can be synthesized by the body from other compounds and are not required directly through the diet. However, some nonessential amino acids become conditionally essential at times of illness or stress when the body's needs are higher.

How Amino Acids Are Used in the Body

Amino acids play a crucial role in many bodily functions. Here are some of the key uses of amino acids:

• Building structural proteins like collagen, elastin and keratin
• Manufacturing hormones, antibodies and enzymes
• Producing heme which is found in hemoglobin
• Synthesizing the nucleotides and nucleic acids used in DNA and RNA
• Acting as precursors for important biological molecules like serotonin, melanin etc.
• Providing a source of energy especially during prolonged starvation
• Maintaining proper nitrogen balance
• Regulating key metabolic pathways related to nutrient absorption and excretion

Without adequate amounts of the essential amino acids, our bodies would be unable to perform these critical functions.

Protein Synthesis

One of the most vital roles of amino acids is in the synthesis of proteins. During protein synthesis, ribosomes in the cell's cytoplasm link individual amino acids together in a specific sequence to form polypeptide chains. This process is directed by the genetic code stored in DNA.

The sequence and the number of amino acids determine the type of protein that is produced. For instance, short chains of amino acids form peptides while longer chains make up structural proteins like collagen or functional proteins like enzymes. More than 40,000 different proteins are produced through unique combinations of the 20 amino acids.

Major Amino Acids and Their Functions

While all amino acids are needed for protein production, some play particularly important roles in bodily processes. Here are a few of the most significant amino acids and their main functions:

Leucine

Stimulates muscle protein synthesis, aids wound healing and produces growth hormones. Leucine is one of three branched-chain amino acids (BCAAs).

Lysine

Needed for proper growth and calcium absorption. Lysine also helps form collagen and aids tissue repair.

Methionine

Acts as a lipotropic agent to prevent excess fat buildup in the liver while protecting cells from toxins. Methionine is a sulfur-containing amino acid.

Tryptophan

Precursor of serotonin which regulates mood, sleep and appetite. Tryptophan also reduces pain sensation.

Glycine

Helps form collagen and glutathione. Glycine serves as a neurotransmitter and is useful for wound healing.

Histidine

Needed for growth and tissue repair. Also protects nerves and helps produce red and white blood cells.

Arginine

Stimulates release of growth hormone, insulin and prolactin. Improves immunity and speeds wound healing.

Benefits of Amino Acid Supplements

In addition to eating high protein foods, taking supplements that contain free-form amino acids can provide benefits for athletes, those recovering from illness and vegetarians or vegans with limited protein intake.

Types of Amino Acid Supplements

There are several categories of amino acid supplements:

• BCAAs - Branched-chain amino acids like leucine, isoleucine and valine help stimulate protein synthesis. Useful for building muscle mass.
• EAAs - Essential amino acid supplements provide balanced ratios of the nine essential amino acids. Helpful for treating muscle loss or malnutrition.
• Individual Amino Acids - Single amino acid supplements like glutamine, arginine or tryptophan. Used for specific therapeutic purposes.
• Hydrolyzed Collagen - Provides high concentrations of glycine, proline and hydroxyproline. Used for improving skin, hair and joint health.
• Protein Powders - Whey, egg, soy or plant-based protein powders supply various amounts of all essential and nonessential amino acids. Help build lean muscle mass when combined with strength training.

Benefits of Amino Acid Supplementation

Taking amino acid supplements, especially essential amino acids, has been shown to provide the following benefits:

• Increases muscle protein synthesis leading to enhanced muscle repair and growth when combined with exercise. Useful for bodybuilders and aging adults experiencing muscle loss.
• Helps maintain a positive nitrogen balance by supplying amino acids needed for tissue growth and repair. Prevents excessive muscle wasting.
• Boosts exercise performance and endurance. BCAA supplements help reduce fatigue and improve training capacity.
• Stimulates release of growth hormone for which amino acids serve as precursors.
• Provides easily digestible nutrition during illness, injury or prolonged fasting when intake from whole foods is inadequate. Helps treat malnutrition in critically ill patients.
• May enhance focus and cognitive function since amino acids like tyrosine affect dopamine and norepinephrine levels.
• Vegetarians or vegans can use certain amino acid supplements to meet higher protein requirements.

Dosage and Timing

Most healthy adults can safely take up to 40 grams of combined essential amino acids per day. Individual amino acids like leucine can be taken up to 5 grams daily.

It's best to take an EAA or BCAA supplement shortly before or after a workout to maximize muscle protein synthesis. A dose of 2-3 grams at both times is ideal. EAAs and BCAAs can also be taken between meals if protein intake was inadequate.

Those recovering from illness or with malnutrition may need higher therapeutic doses under medical guidance. Always follow label directions carefully.

Potential Side Effects

When taken at appropriate dosages, amino acid supplements are generally well tolerated. Possible side effects in sensitive individuals include:

• Stomach upset, diarrhea, nausea
• Dehydration and electrolyte imbalances
• Changes in blood sugar regulation
• Increased ammonia levels

Rare side effects like fatigue, altered heartbeat and dizziness may occur with high doses over 40 grams per day. Consult a doctor before using amino acid supplements if pregnant, breastfeeding or taking medication.

Conditional Amino Acids

While nonessential amino acids can normally be synthesized in the body, during times of illness or metabolic stress synthesis may become impaired. Conditional amino acids like arginine, glutamine, cysteine and taurine then become semi-essential and need to be obtained from the diet or supplements to meet the body's increased demand.

Amino Acid Synthesis and Metabolism

In addition to acquiring amino acids from protein foods, the body can synthesize certain amino acids through cellular processes. Understanding amino acid metabolism helps determine optimal intake needs.

Biosynthesis of Nonessential Amino Acids

The human body can produce 10 of the 20 common amino acids from scratch. The key stages of amino acid biosynthesis include:

• Synthesis starts with simple precursors like glucose, ammonia and other intermediary metabolites.
• Cellular enzymes catalyze reactions to form the amino and carboxyl groups that characterize amino acids.
• Transamination enzymes transfer amine groups from donor amino acids to convert alpha-keto acids into nonessential amino acids.
• Costly metabolic pathways are required to synthesize complex amino acids like tryptophan which is why some amino acids remain essential.

Amino Acid FAQ

What are the 10 nonessential amino acids?

The 10 amino acids that the body can synthesize are alanine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, and tyrosine. These are considered nonessential amino acids.

When should I take amino acid supplements?

Take amino acid supplements shortly before or after exercise to maximize muscle growth. They can also be taken between meals if protein intake at a meal was low. Those recovering from illness may need doses spread throughout the day.

Are amino acid supplements safe?

Amino acid supplements are generally safe at recommended dosages. Side effects are rare but may include nausea, fatigue, diarrhea, and headache in sensitive individuals. Very high doses over 40 grams may have more risks.

How many grams of amino acids per day?

Healthy adults can take up to 40 grams of combined essential amino acids like leucine, lysine and methionine per day. Exceeding this amount could lead to potential side effects. Follow label directions.