The simplest amino acid among the options given is glycine.

Glycine, also known as aminoacetic acid, is the smallest and simplest amino acid. It is considered simple because it has the simplest side chain, consisting of just a single hydrogen atom. The structure of glycine consists of a central carbon atom (alpha carbon) bonded to a hydrogen atom, an amino group (-NH2), a carboxyl group (-COOH), and a hydrogen atom as its side chain.

Glycine is the only amino acid that does not have a chiral carbon, which means it is not optically active and does not have enantiomers. This is because both of its side chain and the hydrogen atom are the same.

Glycine is a non-essential amino acid, which means it can be synthesized by the body itself and does not necessarily need to be obtained from the diet. It plays important roles in the synthesis of proteins, DNA, and many other molecules in the body.

Glycine is known for its important functions in the central nervous system. It acts as an inhibitory neurotransmitter, helping to regulate and balance the excitatory signals in the brain. It is also involved in the synthesis of other neurotransmitters, such as serine and glutathione.

Glycine is commonly found in many protein-rich foods, such as meat, fish, dairy products, and legumes. It is also used as a food additive and supplement due to its various health benefits. It has been studied for its potential effects on sleep, cognitive function, and even certain medical conditions.

In conclusion, glycine is the simplest amino acid among the options provided. Its structure consists of a central carbon atom bonded to a hydrogen atom, an amino group, a carboxyl group, and a hydrogen atom as its side chain. It plays important roles in the body, particularly in the central nervous system, and can be obtained from both dietary sources and synthesized by the body itself.