Collagen is the most abundant protein in the human body. It adds great strength and flexibility to skin, tendons, and ligaments. These qualities are characteristic of structural proteins.

Globular proteins are generally rounded, protecting a nonpolar center from the aqueous environment around the protein. Most cytoplasmic proteins and enzymes are globular proteins. In contrast, fibrous proteins are generally elongated and designed for structural support; collagen is a fibrous protein, in addition to a structural protein. Integral proteins span the plasma membrane, often creating channels.

Proteins are classified into several categories based on where they perform their function. Peripheral membrane proteins span only one side of the lipid bilayer and thus have mobility. Unlike integral membrane proteins, which span the entire lipid bilayer, peripheral membrane proteins have the liberty of traveling from layer to layer as well as flip flop between the two bilayers.

Isomers are molecules that have the same molecular formula, but have different chemical structures. Isomerases are enzymes that are able to rearrange the structure of a molecule while keeping its chemical formula the same.

A protein consists of amino acids. Essential amino acids cannot be synthesized by the body, and must be included in the diet. A protein containing all of the essential amino acids is called a complete protein. An incomplete protein lacks one or more of the essential amino acids.

Neurotransmitters are chemicals that relay messages from one cell to the next. Enzymes are protein catalysts that speed up biological reactions. Minerals are inorganic compounds and are not present in the body in large amounts, with the exception of hydroxyapatite crystal found in bones. Electrolytes are ionic salts in the blood, tissue fluids, and cells, such as sodium, potassium, and chlorine. 

Receptor proteins in a signal transduction pathways can be found both within the plasma membrane or cytosol; as a result, protein Y could potentially function as a receptor. The electron transport chain occurs in the mitochondria, and relies on the movement of electrons; the proteins that “move” these electrons, and subsequently pump protons (creating a gradient), are located in the inner membrane. An antiporter functions in a membrane as well due to its importance in creating and maintaining a concentration gradient. In a similar fashion, nuclear trafficking refers to the regulation or movement of molecules in and out of the nuclear membrane. Last, DNA replication occurs in the nucleus and does not involve a membrane of any sort; therefore, the membrane dwelling protein Y cannot function in this process.