The molecules that make you, you

Amino acids are the fundamental components that make up proteins. Each amino acid contains both an amino group and a carboxylic group, giving them their distinctive chemical properties. These molecules are far more than simple protein components — they actively participate in gene expression by regulating protein functions and facilitating the translation of messenger RNA (mRNA).

Scientists have identified over 700 different amino acids in nature, with nearly all of them being α-amino acids. You can find these versatile molecules throughout the living world: in bacteria thriving in extreme environments, fungi decomposing forest floors, algae floating in our oceans, and plants surrounding us every day.

Think of amino acids like pieces in a sophisticated construction set. While each piece has its own unique shape and properties, they can be combined in countless ways to create something entirely new. Similarly, the 20 standard amino acids each bring their own characteristics to the table, yet they work together to form an almost infinite variety of proteins — from the enzymes that power our metabolism to the antibodies that protect us from disease.

Protein is formed by the joining together, into chains, of amino acids, and thus far over 100,000 different proteins have been identified in nature. The human body alone contains over 50,000 different forms of protein. The total presence of amino acids in the body represents fully three quarters of the body's dry weight. Most of the amino acids in the body can be manufactured out of just eight other amino acids, which are all essential in the diet — meaning our diet must supply free forms of these eight amino acids for life to continue. These essential amino acids are critically important to life and health: out of them the body makes the other amino acids, as well as enzymes, neurotransmitters, mucopolysaccharides, blood, muscles, organs, and bones.

When only a short chain of amino acids is joined together in a particular sequence, it is called a peptide. When the chain is long, it is called a protein. The amino acids themselves are constructed from a combination of the following elements: carbon, hydrogen, oxygen, nitrogen, and in some cases sulphur.

L- and D-Amino Acids

Every amino acid comes in two forms: a 'left-handed' (L) and a 'right-handed' (D) form. These two forms are identical in every respect except for the conformation of the subunits of which they are composed. That is to say, although chemically they contain the same elements in precisely the same quantities and in the same sequence, they are the mirror image of each other — just as the human left hand has the same construction as the human right hand and yet they are different (a right hand cannot wear a left-handed glove, for example). Protein chains cannot be formed from a combination of L and D amino acids.

The body is constructed almost without exception from the L forms of amino acid. However, the D forms, which occur in nature, are often found to have therapeutic value. For example, the D form of phenylalanine is a particularly valuable asset in treating pain.

Abbreviations

To understand amino acid abbreviations, it is important to know why their names have been shortened in the first place. The reason is to make them easy to identify using a more manageable three-letter system. For instance, the simplest amino acid, glycine, is depicted as H—Gly—OH, with the "H" and "OH" representing H₂O at the time of amino acid condensation to form a peptide.

Another way to look at the three-letter abbreviation system is that it captures the amino acid's residual state within proteins and peptides. When the system was introduced, it was thought primarily to save space rather than simplify amino acid names. When the one-letter system is used — such as "G" for glycine, which is more common nowadays — it refers to synthesized peptides from the coded amino acid groups.

How Amino Acids Were Discovered

The amino acids are a result of protein hydrolysis. Throughout the centuries, amino acids have been discovered in a variety of ways, though primarily by chemists and biochemists of high intelligence who possessed great skill, patience, and creativity in their work.

Protein chemistry is age-old, with some processes dating back thousands of years — glue preparation, cheese manufacturing, and even the discovery of ammonia via the filtering of dung all occurred centuries ago. Moving forward to 1820, Braconnot prepared glycine directly from gelatin. He was attempting to uncover whether proteins acted like starch or whether they were made of acids and sugar.

While progress was slow at that time, it has since gained plenty of speed, although the complicated processes of protein composition have not been entirely uncovered even to this day. Much more remains to be discovered in the analysis of amino acids and in the finding of new ones. The future of protein and amino acid chemistry lies in biochemistry — and it is likely that our knowledge will not be fully satiated anytime soon. This adds to the mystery, complexity, and strong scientific value of amino acids.

Experts classify amino acids based on a variety of features, including whether people can acquire them through diet. Scientists recognize three amino acid types: nonessential, essential, and conditionally essential. However, the classification as essential or nonessential does not actually reflect their importance — all 20 amino acids are necessary for human health.

An additional classification depends upon the side chain structure. Experts recognize five categories: Cysteine and Methionine (sulfur-containing); Asparagine, Serine, Threonine, and Glutamine (neutral); Glutamic acid and Aspartic acid (acidic); Arginine and Lysine (basic); and Leucine, Isoleucine, Glycine, Valine, and Alanine (aliphatic), along with Phenylalanine, Tryptophan, Tyrosine, and Histidine (aromatic).

A final classification divides the 20 amino acids into four groups by side chain character: non-polar, polar, acidic-polar, and basic-polar. Side chains with pure hydrocarbon alkyl or aromatic groups are non-polar: Phenylalanine, Glycine, Valine, Leucine, Alanine, Isoleucine, Proline, Methionine, and Tryptophan. If the side chain contains polar groups like amides, acids, and alcohols, the amino acid is classified as polar: Tyrosine, Serine, Asparagine, Threonine, Glutamine, and Cysteine. The acidic-polar group comprises Aspartic Acid and Glutamic Acid; the basic-polar group comprises Lysine, Arginine, and Histidine.

Only 20 amino acids are found in human peptides and proteins. These naturally occurring amino acids are used by cells to synthesize peptides and proteins. They are typically identified by the generic formula: H₂NCHRCOOH. The primary difference between the 20 amino acids is the structure of the R group.

The properties of α-amino acids are complex, yet simplistic in that every molecule involves two functional groups: carboxyl (–COOH) and amino (–NH₂). Each molecule can contain a side chain or R group — Alanine, for example, is a standard amino acid containing a methyl side chain group. The R groups have a variety of shapes, sizes, charges, and reactivities. This allows amino acids to be grouped according to the chemical properties of their side chains.

Amino acids are crystalline solids which are usually water soluble and only sparingly soluble in organic solvents. Their solubility depends on the size and nature of the side chain. Amino acids have very high melting points, up to 200–300°C. Their other properties vary for each particular amino acid.

Isoelectric Points of Amino Acids

The isoelectric point (pI) of an amino acid refers to the pH at which the amino acid exists in its neutral, or zwitterionic, form. At the isoelectric point, the amino acid carries no net electrical charge because the positive charge on the amino group (+NH₃) equals the negative charge on the carboxyl group (−COO−). The isoelectric point is an essential concept in biochemistry and plays a role in various biological processes, including protein behavior and separation techniques.

pI calculation. The pI is the pH at which an amino acid is electrically neutral. For amino acids with ionizable side chains, determining the pI involves considering the ionization of the amino and carboxyl groups, as well as the side chain (R-group). For example, the pI of glycine is around 5.97, while the pI of lysine, with a basic side chain, is approximately 9.74.

The isoelectric point is crucial in the study of proteins and their behavior in different environments. Techniques like isoelectric focusing use the principles of the isoelectric point to separate proteins based on their pI values in an electric field.

Zwitterionic Form of Amino Acids

Since the amino and the acidic groups have opposite electrical charges, an amino acid (an amphoteric electrolyte) acts as both a base and an acid by accepting and supplying a hydrogen ion, respectively. Thus, all amino acids form intramolecular salts both in the crystalline state and in aqueous solution. This structure, in which a molecule has both positive and negative electrical charges, is known as a dipolar ion or zwitterion. Uncharged (nondissociated) forms of amino acids almost do not exist.

For example, the ratio of charged dipolar (ionized α-amino and α-carboxyl groups) to uncharged forms of L-aspartic acid in aqueous solution is approximately 28,000:1 at pH 7.0. Similarly, the proportion of charged dipolar to uncharged forms of L-lysine in aqueous solution is approximately 320,000:1 at pH 7.0.

Individual types of amino acids have particular characteristics. Some are capable of influencing body processes because they are essential to the formation of neurotransmitters — substances used in the brain and by the nervous system to increase or decrease the efficiency and rapidity of nerve transmission. The ability of the brain to receive and transmit messages depends upon these neurotransmitters, which are themselves dependent upon particular amino acids. All functions of the body depend upon sound nervous interconnection. The coordination and regulation of all the millions of messages that are constantly going on in the body depend upon neurotransmitters and therefore on amino acids. Some of the neurotransmitters have a stimulating, excitatory function; others have a calming, inhibitory function.

The scope and use of appropriate amino acids in therapy can therefore be seen to be enormous. Unless all the amino acids, in their free form, are present in adequate amounts, there will be imbalances in neurotransmitter function, and a variety of nervous and emotional problems will result. The very energy of the brain is dependent upon certain amino acids. Tryptophan and phenylalanine are both of profound importance in their relation to brain and nerve function.

Another major area of activity of some amino acids is as detoxifiers of the body. The sulphur-rich amino acids — methionine, cysteine, and cystine — are especially capable of this sometimes life-saving task. They have the ability to chelate (lock onto) heavy metals such as lead, mercury, and aluminium, which are toxic to the body, and to actually remove them from the system.

They are also capable of damping down damaging oxidative processes in the body. When toxic substances are present in tissue or in the bloodstream, there is potential for free radical damage, as fractions of the oxidizing substance cascade around the area creating tissue damage. These processes — thought to result in cell changes as occur in arteries before they become atherosclerotic, and in cells before they become cancerous — are controlled by free radical scavengers, of which the sulphur-rich amino acids are a major part. Vitamins A, C, and E and the mineral selenium are also anti-oxidants which reduce free radical damage.

Glucogenic Amino Acid

A glucogenic amino acid, also known as a glucoplastic amino acid, is an amino acid capable of undergoing conversion into glucose through the process of gluconeogenesis. This stands in contrast to ketogenic amino acids, which are transformed into ketone bodies.

The conversion of glucogenic amino acids into glucose follows a two-step process. Initially, these amino acids are transformed into alpha-keto acids. Subsequently, these alpha-keto acids undergo further conversion into glucose. Both of these crucial processes take place primarily in the liver. This mechanism becomes particularly prominent during catabolism, becoming more pronounced as the severity of fasting and starvation increases.

In humans, the glucogenic amino acids are: Alanine; Arginine; Asparagine; Aspartic acid; Cysteine; Glutamic acid; Glutamine; Glycine; Histidine; Methionine; Proline; Serine; Valine.

Ketogenic Amino Acid

A ketogenic amino acid is an amino acid capable of being directly degraded into acetyl-CoA. Acetyl-CoA serves as the precursor for ketone bodies and myelin, particularly crucial during early childhood when there is a heightened demand for myelin synthesis in the developing brain. Unlike glucogenic amino acids, ketogenic amino acids cannot be converted into glucose, as both carbon atoms in the resulting ketone bodies are ultimately metabolized into carbon dioxide through the citric acid cycle.

In humans, two amino acids — leucine and lysine — are exclusively ketogenic. Additionally, there are amino acids with dual characteristics, being both glucogenic and ketogenic, referred to as amphibolic. A helpful mnemonic for remembering these is "PITTT": phenylalanine, isoleucine, threonine, tryptophan, and tyrosine.

Amino Acid Catabolism

Amino acid catabolism, also known as amino acid degradation, is a fundamental process that involves the breakdown of amino acids into simpler molecules. This intricate biochemical pathway is essential for maintaining nitrogen balance, generating energy, and providing intermediates for various metabolic processes.

Essential amino acids can be obtained by maintaining a protein-rich diet, available in various plant and animal foods.

Complete proteins, containing all 20 or more types of amino acids, are present in certain foods. Examples include red meat, chicken, fish, seafood, eggs, milk, cheese, yogurt, quinoa, chia seeds, and tofu. These foods are comprehensive sources of essential amino acids.

Conversely, some foods are incomplete proteins, lacking one or more of the nine essential amino acids. Plant-based sources like grains, nuts, seeds, beans, legumes, fruits, and vegetables fall into this category. If you follow a vegetarian or vegan diet, incorporating a variety of these incomplete proteins is essential to ensure the intake of all necessary amino acids.

Amino Acid Supplements: Supporting Health and Wellness

Amino acid supplements have gained popularity for their diverse benefits across different age groups and health goals. From promoting muscle growth to aiding in weight loss and enhancing hair health, these supplements play a crucial role in overall well-being.

For Women and Kids. Amino acid supplements tailored for women and kids cater to specific nutritional needs, supporting growth, development, and overall health maintenance. They are formulated to provide essential nutrients necessary for energy production and immune function.

For Weight Loss. Amino acid supplements are increasingly recognized for their potential to aid in weight loss efforts. By supporting metabolism and suppressing appetite, they can assist in achieving and maintaining a healthy weight, making them a valuable addition to weight loss regimens.

For Bodybuilding and Muscle Growth. Athletes and fitness enthusiasts often rely on amino acid supplements to support muscle recovery and growth. Branched-chain amino acids (BCAAs) and essential amino acids (EAAs) are particularly beneficial for enhancing protein synthesis and reducing muscle fatigue.

In considering amino acids in relation to health and ill health there are two main areas to cover. The first looks at particular conditions relating to disorders of amino acid metabolism, resulting in a related pathological state. The second area, and the one which attracts the major interest among nutritionally oriented practitioners, is that involving conditions not specifically related to diseases of amino acid metabolism, and yet which appear to respond positively to dietary manipulation involving the intake of particular amino acids and other nutrients.

Such conditions as certain forms of depression, insomnia, herpes infections, weight problems, fat metabolism dysfunction, and epilepsy have all been shown to improve, in suitable cases, by the use of appropriate amino acid therapy. Certain physiological functions have also been enhanced by the selective use of amino acids. These include detoxification of heavy metals, modification of free radical activity, and enhanced mental function via neurotransmitter stimulation.

The ability of the brain neurons to manufacture and utilize a number of neurotransmitters — such as serotonin, acetylcholine, and the catecholamines dopamine and norepinephrine — is dependent upon the concentrations of both amino acids and choline in the bloodstream. This largely depends upon the food composition at the previous meal. Since the brain is apparently unable to make adequate quantities of amino acids and choline to meet its requirements for neurotransmitter synthesis, it is vital that adequate quantities of these precursors are present in the circulation. The dry material of the brain comprises more than one third protein, and stress can create a situation in which non-essential amino acids cannot be adequately produced to meet its needs — a situation that can result in a range of mental and emotional symptoms such as depression, apathy, and irritability.