Many of the D-amino acids found in nature have been discovered in bacterially produced peptides that have antibiotic properties. Bacteria secrete these peptides into their environments to kill competitor bacteria and thereby gain a selective advantage. Given your answer to part (a) of this question, what potential advantages might D-amino acids confer to a secreted peptide toxin

D-amino acids are less likely to be recognized by proteolytic enzymes thereby they are not degradated.

Explanation:

Peptides are a type of polymers formed by joining several amino acids by means of peptide bonds. They are responsible for a large number of important cellular functions for the organism. Amino acids are thus the monomers that make up peptides and consist of an amino group (-NH2) at one end of the molecule and a carboxyl group (-COOH) at the other end.

Antibiotics are chemical substances produced by a living being (although they can also be synthetic derivatives made in laboratories), which kill or prevent the growth of certain kinds of sensitive microorganisms and are generally drugs used in the treatment of bacterial infections.

All amino acids, except glycine, are stereoisomers which means that there are nonoverlapping mirror images of their structure. These are labeled L (left-handed) and D (right-handed) to distinguish mirror images. A mirror image, for example, compares a right foot with a left foot. They are similar, but not exactly the same, they are like mirror images of each other. However, we could not, for example, put a right shoe on a left foot and vice versa. The same analogy applies to stereoisomers, they are similar but not superimposable, which means that not all compounds will act in the same way in an L or D molecule. For some reason, the amino acids that make up the proteins in human bodies are all L-amino acids.

To distinguish an L-amino acid from a D-amino acid, we must look at the α-carbon, which has four substituents forming a tetrahedron. then we must identify the hydrogen bonded directly to this carbon. In this way they are numbered and following the numbering order, they are classified as L or D.

Bacteria that secrete D amino acids kill other bacteria in the environment that might compete with them for resources, because they have antibiotic properties. These D amino acids are not usually recognized by proteolytic enzymes in organisms that degrade peptides or proteins. So the amino acid remains in the environment fulfilling its function, which is an antibiotic function to fight against other bacteria. Peptide toxins also fulfill this function, however, if they are destroyed by proteases.