BeerSci: What Beer’s Key Ingredient Reveals About Our Own Genomes
The yeast S. cerevisiae is instrumental in brewing ale. But did you know that it’s also instrumental in helping scientists better understand cells?
Humans have been exploiting S. cerevisiae's fermentation prowess for thousands of years. Without it we wouldn't have beer, bread or wine. In addition to its uses in food production, S. cerevisiae is also an amazing tool for molecular and cell biology, one that is helping scientists suss out the rules of how our cells work and gain clues to what happens at the molecular level when things go wrong.
That’s because S. cerevisiae is one of the simplest eukaryotic cells—cells like those that make up your dog, your houseplants or your local bartender. In fact, in 1996 S. cerevisiae became the first eukaryote to have its genome sequenced. According to the Saccharomyces Genome Database, S. cerevisiae's genome has some 12,100,000 base pairs and some 6,600 open reading frames (that is, places in the genome that could possibly contain a gene).
Most of you, I am sure, remember that there are two general kinds of cells: prokaryotic and eukaryotic. That is, “no nucleus” and “has a nucleus.” That’s all true, but the differences between the two kinds of cells are much more profound than that. Bacteria — prokaryotes — organize their genetic material in a completely different (and much simpler) way than do eukaryotes. Prokaryotes usually only have a chunk of DNA for a genome — usually circular — and a few extra chunks, called plasmids, kicking around in the cytosol. Those plasmids are really useful in doing things like sharing genes between bacteria, and its how one antibiotic-resistant strain of bacteria can pass along antibiotic resistance to a bunch of nigh-unrelated strains of bacteria in, say, your intestines. The genes in bacteria are generally read exactly as they are found in the DNA, kind of like how you’re reading this sentence. No intervening clumps of letters to clutter things up.
Eukaryotes, on the other hand, bundle up all that DNA (and they have a lot of it) into a protein-DNA complex called chromatin, then wind that chromatin into individual chromosomes. Further, the genes are constructed in such a way that they must be heavily processed before they can ever “code” for a functional protein. Much of what we understand about eukaryotic cellular processes and eukaryotic gene expression, we learned by studying the molecular mechanics of S. cerevisiae.
