What kind of isomers can amino acids form? Which isomer is present in most living organisms?
Amino acids can exist in two isomeric forms: L-isomers (levo, or left-handed) and D-isomers (dextro, or right-handed). The isomer that is present in most living organisms is the L-isomer.
To understand this, we first need to know that amino acids are chiral molecules, meaning they have a non-superimposable mirror image. Just like your left and right hand, these mirror images cannot be perfectly overlapped. In the case of amino acids, this chirality arises from the central carbon atom, known as the alpha carbon, which is bonded to four different groups: an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom (-H), and a unique side chain (-R).
Now, to determine which isomer is present in most living organisms, we turn to the principles of biochemistry and evolution. Life on Earth originated from a common ancestral organism, and over time, the enzymes and proteins involved in living systems evolved to recognize and utilize specific enantiomers of molecules, including amino acids.
During the evolution of life, the enzymes and proteins that interact with amino acids have adapted to preferentially recognize and use the L-isomer. This is why the L-isomer of amino acids is more abundant in biological systems. These L-amino acids are the building blocks for proteins and are essential for the structure and function of living organisms.
In summary, amino acids can exist as L-isomers (left-handed) and D-isomers (right-handed). The L-isomer is the predominant form present in most living organisms due to the evolutionary adaptation of enzymes and proteins to utilize these specific enantiomers.