Amino Acid Structure: Definition, Structure, Basicity of Amino Acid

Amino acids are the organic compounds. They combine and form proteins. The general formula for amino acids is R-CH(NH2)-COOH. Amino acids consist of amine and functional groups of carboxyl. It also includes side chains consisting of R groups (“R” can represent any alkyl or aryl group). These R groups distinguish amino acids and are responsible for their unique properties.

Structure Of Amino Acid

It is not uncommon to find other elements on the side chains of amino acids. It can also be said that more than 500 naturally occurring amino acids are known. Of these, only 20 are known to exist in the genetic code.

In the human body, these biomolecules are involved in many biological and chemical functions and are important factors in human growth and development. Amino acids usually have very high melting and boiling points. They are usually in the form of white, crystalline, stable compounds. Some amino acids are known to be sweet, tasteless, and bitter. Most amino acids are soluble in water. However, it can also be said that most amino acids are insoluble in organic solvents.

Common Amino Acids And Their Structures

1. Glycine

Glycine is an amino acid containing only one hydrogen atom in its side chain. It is known to be the simplest amino acid with the chemical formula NH2-CH2-COOH (because carbamates are known to be unstable). Glycine is known as a proteinogenic amino acid. Due to its compact shape, glycine is an integral part of alpha-helix formation in protein secondary structure. By the same description, it is the most abundant amino acid in the triple helix of collagen. Impairments of its release in the spinal cord, such as tetanus infection, can cause spastic paralysis due to uncontrolled muscle contraction.

2. Serine

Serine is an alpha amino acid commonly used in protein biosynthesis. It consists of an α-amino group that exists in the protonated NH3 form under biological conditions. It also contains a carboxyl group that exists in the deprotonated -COO- form under biological conditions. Serine contains a side chain that consists of a hydroxymethyl group. Therefore, it can be classified as a polar amino acid. Under normal physiological conditions, it is a non-essential amino acid because it can be synthesized by the human body.

3. Leucine

Leucine is an important amino acid used in protein biosynthesis. Leucine is an α-amino acid and has an α-amino group (which exists in the protonated -NH3 form under biological conditions), an α-carboxylic acid group (which exists in the deprotonated -COO- form under biological conditions) , and the isobutyl group on the side chain make it a non-polar, aliphatic amino acid. It is an essential amino acid for humans and cannot be synthesized by the body.

Therefore, it must come from food. Protein-producing foods such as dairy products, meats, beans, soy products, and other legumes are human dietary sources of this amino acid.

4. Cysteine

Acting as a nucleophile, the thiol side chain of this amino acid is also involved in several enzymatic reactions. The disulfide derivative cystine, which is known to play an important structural role in many proteins, is known to be susceptible to oxidation by thiols. Cysteine generally has the same structure as serine, but one of its oxygen atoms is replaced by sulfur. Selenocysteine is obtained by replacing the same oxygen atom with selenium instead of sulfur.

Cysteine, like other common amino acids, is found in most protein-rich foods, along with the oxidized dimeric form of cystine. Cysteine is listed as a non-essential amino acid. It may be essential in rare cases for the elderly, children, and those with certain metabolic disorders or malabsorption syndromes. Under normal physiological conditions, as long as sufficient amounts of methionine are available. Cysteine is normally synthesized by the human body.

5. Valine

Valine is an important amino acid used in protein biosynthesis. Valine is an α-amino acid, consisting of the α-amino group (which exists in the protonated -NH3 form under biological conditions), the α-carboxylic acid group (which exists in the deprotonated -COO- form under biological conditions) and a side chain containing an isopropyl group. Therefore, it can be called a non-polar aliphatic amino acid.

Most Basic Amino Acids

There are three amino acids with side chains that are basic at neutral pH. These are arginine, lysine and histidine.