NASA is blasting a satellite into orbit Thursday carrying a microlaboratory full of yeast to test whether certain organisms are more resistant to drugs in outer space. According to the New York Times, "[y]east is used often for studying fundamental biological questions." Why is yeast so handy?
Because its cells are similar to human cells but grow a lot faster. The most common use of yeast, aside from baking bread and brewing beer, is to test how a particular drug or chemical or enzyme affects unicellular organisms. Like human cells, yeast cells have a typical eukaryotic structure, including a nucleus, cytoplasm, and mitochondria. * Yeast also shares many genes with human cells, so if you want to find out what a particular drug does to a certain human gene, you can often test it on yeast cells first. (That's not always an option: Yeast has about 6,000 genes, while the human genome has about 25,000.) And while human cells divide a rate of about once every 12 hours, yeast divides once every two hours or so. That means scientists can grow cultures and complete experiments many times faster with yeast than with human material.
Yeast is also incredibly flexible. There are thousands of different species and strains, each with its own genetic makeup. Many researchers use Saccharomyces cerevisiae, or simple baking yeast. But one of the most attractive characteristics of yeast is that you can customize it. Say you want to study one particular gene: You can buy a strain with that gene "knocked out," or eliminated, to see what happens when it's gone. (For all your yeast-strain needs, go here.) For example, yeast cells and cancer cells share a gene that targets certain drugs and pumps them back out, making them resistant to treatment. When you remove the gene, the cell stops pumping. You can also knock out individual yeast genes and replace them with human genes. (The yeast will usually grow just as quickly.) Drugs intended for humans eventually have to be tested on human tissue cells, too. But researchers can work out a lot of the kinks with yeast alone.
Another advantage of using yeast: It's safe. Many organisms, particularly bacteria, are dangerous to work with: Scientists have to use anti-contamination methods like a laminar flow cabinet. Most yeast, on the other hand, is harmless. Granted, certain strains can cause mild skin irritation (think "yeast infection"), and there are even some that can be fatal if ingested or inhaled. But those types aren't used in everyday research.
Finally, yeast is useful because we already know so much about it. There's a snowball effect: The more research that is conducted with yeast, the more informed and controlled future research can be. Yeast has played a role in scientific discoveries as far back as the early 1900s. In 1907, German scientist Edward Buchner won the Nobel Prize in Chemistry for research involving yeast extract and fermentation. In 2006, Roger D. Kornberg won the same prize for a major breakthrough in DNA transcription using a yeast-based procedure. In 1996, yeast became the first eukaryote to have its genome fully sequenced, making it even more useful for scientific testing.
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Explainer thanks John Aris of the University of Florida, Yuri Chernoff of Georgia Tech, and Barbara Hoopes of Colgate University.
Correction, May 8, 2009: This article originally stated that human cells have cell walls. (Return to the corrected sentence.)