In some metabolic reactions, large molecules are made up of smaller ones, as shown in
the simple diagram provided. Which monomer subunits join together to form a protein in a metabolic reaction? (A) Amino acids, (B) glucose, (C) peptin, (D) cellulose, or (E) lipids.
This question asks us about a metabolic reaction in which smaller molecules are
joined together to form larger ones. Metabolism describes all of the metabolic, or chemical, reactions that occur within
living organisms to maintain life.
You might have learned that metabolic reactions can be grouped into those that are
catabolic and those that are anabolic. Catabolic reactions break the bonds in large complex molecules, breaking these
molecules down into their smaller subunits. The breaking of bonds in catabolic processes releases energy, which is temporarily
stored in cells in the form of a molecule called ATP with high-energy bonds. These high-energy bonds can be quickly broken so the energy they store can be easily
accessed when needed. In contrast, anabolic reactions form bonds between small molecules, joining them
together to form larger molecules. The formation of these bonds requires an input of energy, which is supplied by
This question presents us with an example of an anabolic reaction. A large molecule, a protein, is formed from multiple smaller molecules. Proteins are polymers, made up of many monomers. The word monomer contains the prefix mono-, which means one, while the prefix poly-
means many, referring to the fact that polymers are made up of many repeating
subunits of monomers. The specific monomers of proteins are called amino acids. And there are 20 different amino acids that organisms can use to construct different
proteins. The unique properties of each protein are due to the different interactions between
the amino acids they contain.
Now that we have reviewed some basics of metabolism, we are able to answer our
question correctly. The monomer subunits that join together to form a protein in a metabolic reaction are
(A) amino acids.