Question

RECALL Which amino acid is technically not an amino acid? Which amino acid contains no chiral carbon atoms?

Short answer

Glycine; Glycine

Step-by-step solution

Identify Non-Amino Acid

Amino acids typically have an amine group, a carboxyl group, and a unique side chain. Technically, glycine is not considered a standard amino acid because its side chain is just a hydrogen atom, lacking complexity.

Amino Acid with No Chiral Carbon

A chiral carbon atom is one that has four different groups attached to it. In glycine, the central carbon is attached to two hydrogen atoms, an amino group, and a carboxyl group, meaning it has no chiral center.

Key concepts

glycine

Glycine is one of the simplest amino acids and has the chemical formula C₂H₅NO₂. It is the only amino acid that does not have a chiral carbon atom. Glycine is unique because its side chain is only a single hydrogen atom.
This simplicity makes glycine crucial for studying basic biochemistry concepts as it can be easily modeled and understood.
It is often used in studies to explore the general characteristics of amino acids and proteins.

chiral carbon atom

A chiral carbon atom, also known as an asymmetric carbon, is a carbon atom that is attached to four different groups. This unique attachment leads to a property called chirality, allowing the molecule to exist in two mirror-image forms called enantiomers.
These enantiomers can have different biological activities and properties. Chirality is essential in biochemistry and pharmacology because the different forms can have entirely different effects in biological systems.

amino acid structure

The general structure of an amino acid includes:

• An amino group (-NH₂)
• A carboxyl group (-COOH)
• A central alpha carbon
• A unique side chain (R group)

The central alpha carbon is what makes amino acids distinct from each other; attaching different R groups yields different amino acids.
This simple structure allows them to polymerize and form proteins, which are essential for countless biological functions, such as enzyme activity and structural support.

non-chiral amino acid

Among the twenty standard amino acids, glycine is the only one that is non-chiral. This is because its side chain is a hydrogen atom, leading the central alpha carbon to be bonded to two identical hydrogen atoms.
Without the presence of four distinct groups attached to the central alpha carbon, glycine lacks chirality, making it simpler and unique compared to other amino acids.
This lack of chirality makes glycine a key reference point in the study of protein structures and functions.