Why are Amino Acids Important in the Human Body?

Biomolecules that are organic compounds containing carbon, hydrogen, and oxygen are known as Amino acid. As the name suggests they also contain two functional groups—an amino group (-NH2) which is basic, and a carboxyl group (-COOH) which is acid in nature.

There are around 300 amino acids that are found in nature, however, only 20 out of these are found in the structure of proteins isolated from different life forms- animal, plant, and microbial. These are called standard amino acids. This is because of the universal nature of the genetic code available for the incorporation of only 20 amino acids when the proteins are synthesized in the cells. This process is controlled by DNA. After protein synthesis, some of the incorporated amino acid undergo modifications to form their derivatives.

General Structure of Amino Acids

If in an amino acid both the carboxyl group and the amino group are attached to the same carbon atom, it is termed as the α-Amino acid. This α-carbon atom binds to a side chain (represented as R) which is different for each of the 20 amino acids. In the biological system, amino acid mostly occurs in ionized form.

Classification of Amino Acids

These are classified in four ways:

1. On the basis of polarity
2. On the basis of structure
3. On the basis of necessity in diet
4. On the basis of the metabolic fate

Amino acids on the basis of Polarity

On the basis of polarity, these biomolecules are classified into 4 groups.

1. Non-Polar Amino Acids– These biomolecules are hydrophobic (water-hating). They do not have any charge on the side chain or the ‘R’ group. the ‘R’ group. Amino acid in this group includes— alanine, leucine, isoleucine, valine, methionine, phenylalanine, tryptophan, and proline.
2. Polar Amino Acids with No charge on ‘R’ group– as per the name these biomolecules have no charge on the ‘R’ group. However, they do have groups like hydroxyl, sulfhydryl, and amide, and they participate in the hydrogen bonding of protein structure. The simple amino acid glycine (where R = H) is also considered in this category.
   The amino acid in this group— glycine, serine, threonine, cysteine, glutamine, asparagine, and tyrosine.
3. Polar Amino Acids with Positive Charge on the ‘R’ group– The three amino acids lysine, arginine and histidine is included in this group.
4. Polar Amino Acids with Negative Charge on the ‘R’ group– The dicarboxylic monoamino acids—aspartic acid and glutamic acid are considered in this group.

Amino acid based on the Structure

Each amino acid is given 3 letters or 1 letter symbol that are commonly used to represent them in the protein structure. The 20 amino acids found in protein are divided into seven groups.

Nutritional Classification of Amino acids

The 20 amino acids are required for the synthesis of a variety of proteins in the body and biological functions, however, all of these biomolecules are not necessarily need to be taken into the diet. Based on nutritional requirements amino acids are divided into two groups.

• Essential or Indispensable amino acids- These biomolecules cannot be synthesized by the body and thus they must be taken through diet. They are required for the proper growth and maintenance of the individual. 10 amino acids come under this category:

1. Arginine
2. Valine
3. Histidine
4. Isoleucine
5. Leucine
6. Lysine
7. Methionine
8. Phenylalanine
9. Threonine
10. Tryptophan

Mnemonic to remember- Any Help In Learning These Little Molecules Proves Truly Valuable

Out of these 10 amino acids- Arginine and Histidine are considered semi-essential because they can only be synthesized by adults and not by growing children. These 8 biomolecules are absolutely essential, while 2 are semi-essential.

2. Non-essential or dispensable aminoacids: The body can synthesize about 10 amino acids to meet the biological needs; hence they are not required to be consumed in the diet.

These are—glycine, alanine, serine, cysteine, aspartate, asparagine, glutamate, glutamine, tyrosine, and proline.

Amino Acid based on their metabolic fate

The carbon skeleton of the amino acids can be used by the body to synthesize glucose (glycogenic) or fat (ketogenic), or both. On the basis of the metabolic fate of amino acids, they are divided into 3 categories:

1. Glycogenic amino acids: These amino acids can serve as precursors for the synthesis of glucose or glycogen. e.g. alanine, aspartate, glycine, methionine, etc.
2. Ketogenic amino acids: These amino acids can be used to synthesize fats. The amino acids leucine and lysine are exclusively ketogenic.
3. Glycogenic and ketogenic amino acids: Four amino acids- isoleucine, phenylalanine, tryptophan, and tyrosine are precursors for the synthesis of glucose as well as fat.

References –

www.ncbi.nlm.nih.gov
en.wikipedia.org