Inside every yeast cell are 16 unique chromosomes, each of which is composed of hundreds of thousands of DNA nucleotides—As, Ts, Cs, and Gs. Encoded on these nucleotides are thousands of genes, each of which contains the information to produce a unique protein that performs a specific biological function. Every yeast cell contains about 7,000 genes, which means that each cell can make about 7,000 unique proteins.
Many of these proteins function as enzymes, meaning that they catalyze specific chemical reactions that help the cell survive and grow. Often, the products of these reactions are responsible for the flavor of fermented beverages produced by yeast, like beer and wine. For example, on chromosome XV of every brewer’s yeast cell, there is a gene called Alcohol-Acyltransferase-1 (ATF1), which encodes the enzyme Atf1. Note that by convention, a gene is abbreviated with capital letters (e.g. ATF1), whereas the protein that a gene encodes is abbreviated with lowercase letters (e.g. Atf1). During beer fermentation, the Atf1 enzyme catalyzes a chemical reaction in which isoamyl alcohol and acetyl-CoA are combined to form isoamyl acetate (Figure 1). Isoamyl acetate imparts banana-like flavors in beers, and is one of the most important flavor molecules in Wit beers and Hefeweizens.
Figure 1. Formation of isoamyl acetate by the Atf1 enzyme.