Lysine is an amino acid, one of the molecules that link together to form proteins. It is classified as an “essential” amino acid because the human body cannot produce it, making it a necessary component of our diet. We must obtain lysine from food sources to build and repair tissues, produce enzymes, and carry out other functions that rely on proteins.
The Core Components of Lysine
Every amino acid has a standard backbone, and lysine is no exception. This consists of a central carbon atom (the alpha-carbon) bonded to four different groups: a basic amino group (-NH2), an acidic carboxyl group (-COOH), and a single hydrogen atom. This shared structure allows amino acids to link into the long chains that form proteins.
Lysine is distinguished from other amino acids by its unique side chain, or R-group. The side chain is a four-carbon chain ending with a second amino group (a butylamine group). This molecular arrangement gives lysine its chemical formula: C6H14N2O2. This side chain dictates lysine’s functions within a protein.
A labeled 2D diagram of L-lysine, highlighting its key functional groups.
Chemical Properties Derived from Structure
Lysine’s chemical behavior is a direct result of its side chain. This second amino group classifies lysine as a basic amino acid. At the neutral pH of the human body (around 7.4), both of lysine’s amino groups become protonated by accepting a proton. This protonation imparts a positive charge to the side chain.
The resulting charge makes the lysine molecule polar. Polar molecules are hydrophilic, meaning they interact favorably with water. This property allows lysine on a protein’s surface to interact with the surrounding water inside a cell.
Role in Protein Formation and Function
While its core groups form the protein’s primary chain via peptide bonds, its side chain handles more complex interactions. The positive charge on its side chain is important for establishing a protein’s three-dimensional shape, or tertiary structure. The positively charged side chain allows lysine to form strong ionic bonds (salt bridges) with negatively charged amino acids like aspartate and glutamate. These salt bridges act like internal clasps, locking the protein into its stable, functional conformation.
The lysine side chain is also a target for post-translational modifications. Processes like acetylation and ubiquitination attach chemical groups to the side chain, which can alter a protein’s function, regulate its location, or mark it for degradation.