The artificial sweetener aspartame is a slightly modified dipeptide. Which two amino acids are used to make it?

Aspartame, a popular artificial sweetener, is composed of two amino acids: aspartic acid and phenylalanine. These building blocks of protein are crucial for various biological functions, and aspartame cleverly mimics the sweetness of sugar by utilizing their properties.

Amino acids are organic compounds that serve as the substrates for peptides and proteins. Each amino acid has a common core structure, characterized by a central carbon (C) atom, also known as the \(\alpha\)-carbon, bonded to four different groups: an amino group (\(NH_2\)), a carboxyl group (\(COOH\)), a hydrogen atom, and a distinctive side chain or R-group, which varies among different amino acids.

Aspartic acid, for instance, has a side chain with a second carboxyl group, making it acidic. Phenylalanine, on the other hand, features a benzyl side chain, responsible for its non-polar character. The pairing of these particular amino acids gives aspartame its unique sweet taste and characteristics.

The link between the amino acids in aspartame is known as a peptide bond, which forms when the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water in a process called dehydration synthesis.

This linkage is characterized by a covalent bond that establishes the backbone of protein structures. Specifically, a peptide bond is an amide type of linkage, where the nitrogen atom of one amino acid binds to the carbon atom of the other's carboxyl group. Represented chemically, the bond is between the \(C=O\) of one amino acid and the \(NH\) of the next, creating the sequence \( -CO-NH- \).

The properties of this bond are central to the behavior of proteins and peptides; it is rigid and planar, and its formation is a key step in protein biosynthesis. In aspartame, the linkage of aspartic acid and phenylalanine through a peptide bond is what classifies it as a dipeptide.

A dipeptide is a molecule consisting of two amino acids linked by a single peptide bond. This structure is the simplest form of peptides, which are the building blocks for larger protein molecules.

In the context of aspartame, the dipeptide is formed by the amino acids aspartic acid and phenylalanine. The chemical composition and structure are meticulously crafted to mimic sweetness while preventing the intake of excess calories. A key feature of dipeptide molecules is their ability to exhibit characteristics of each individual amino acid in addition to properties arising from their combined structure.

The structure of dipeptides allows them to be versatile in their functions and interactions. For example, aspartame's structure enables it to interact with taste receptors in a way that closely replicates the sweet taste of sugar, thereby providing sweetness without the same caloric content of traditional sugars.