Question

How many naturally occurring amino acids are there?

Answer 1

Amino acids are the building block of proteins. These are the organic molecules that have- a carboxyl functional group, an amine functional group, and a side chain.

Complete answer:
The special organic molecules used by living organisms to make proteins are called amino acids. Their structure consists of
1)A basic functional group- Amine ($-NH_2$)
2)An acidic functional group- Carboxylic acid (-COOH)
3)A hydrogen atom- (H)
4)An organic group or side chain (-R).

The side chain of the amino acids is specific to each amino acid. The main elements in their structure are- Carbon, hydrogen, oxygen, nitrogen, and various other elements that- change according to the side chain of the amino acids. They combine to form proteins in our body that help in the- coordination of metabolic reactions, various body functions, formation and maintenance of the body tissues, controlling the activity of genes, and other life-sustaining activities.
The amino acids are amphoteric molecules as they contain both- acidic and basic properties.

They can be divided into various categories based on various properties.
1)Based on their polarity- Polar amino acids (Glycine, Alanine) and Non- polar amino acids (Serine, Cysteine).
2)Based on the nature of their side-chain- Acidic amino acids (Aspartic acid, glutamic acid) and Basic amino acids (Arginine, Histidine, Lysine), Neutral (Serine, Asparagine).
3)Based on the aromaticity of their side-chain- Aromatic amino acids (Phenylalanine and Tryptophan) and Aliphatic amino acids ( Proline and Methionine).
4)Based on their origin- Naturally-occurring amino acids and Synthetic amino acids.
5)Based on their synthesis- Essential amino acids and non-essential amino acids.
The naturally occurring amino acids are found in nature, and their number is approximately 500. Out of all these amino acids, only 20 amino acids are found and used in the genetic code.

Therefore, there are 20 naturally occurring amino acids. These naturally occurring amino acids can be classified into- Essential amino acids and Non- essential amino acids. The amino acids which can be synthesized in our body are called Non-essential amino acids. They are 11 in number, and their names are- arginine, glutamine, tyrosine, cysteine, glycine, proline, serine, ornithine, alanine, asparagine, and aspartate. The amino acids which cannot be synthesized in our body and must be obtained through diets or outer sources are called- Essential amino acids. They are 9 in number, and their names are- histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
These 20 amino acids are coded by- 61 codons and thus, prove the- degeneracy of the genetic code.

Note: The unit of the genetic code formed by a sequence of three nucleotides is called the Codon, and it shows various properties like- Degeneracy. The genetic code is degenerate because the genetic material (DNA or RNA) contains four bases and a codon has three nucleotides. Therefore, more than one codon codes for an amino acid but, each codon is specific to their amino acid. Three stop codons do not code for any amino acid.