Yeast are fungal microbes that have been used by civilization for thousands of years. They are typically non-pathogenic, with exceptions being common skin and vaginal infections, and are easy to cultivate making them easy to harvest. Whether it’s for baking, brewing, brandy, bowels, or biological research, yeasts are very important for two reasons: they undergo alcoholic fermentation and they are one of few eukaryotic cells that can be used for genetic recombination.
As explained in my last video blog, humans (and all eukaryotic organisms for that matter) need oxygen to create energy. When we are using more energy and oxygen than our body can produce at one time, our cells cannot use aerobic respiration to make energy and start undergoing anaerobic respiration. This often happens when we exercise, which is good for you, or if we’re very close to death, which is not so good for you.
Anaerobic respiration in normal eukaryotic cells such as ours results producing lactic acid and carbon dioxide as waste products. This is known as lactic acid fermentation. However, anaerobic respiration in yeast produces ethanol in a process known as ethanol fermentation or alcoholic fermentation. Only yeast and a bacteria called Z. Mobilis are known to undergo alcoholic fermentation.
Wine and brandy made by fermentation of yeast converting the natural sugars present in fruits, especially grapes. Beer and whiskey are made from grain starches that have been converted to sugar.
Ethanol fermentation is also important in making bread rise. It’s not the ethanol, but the carbon dioxide being baked that creates the bubbles and allows the dough to rise. Nearly all the ethanol is evaporated from the bread while it’s being baked.
Yeast is also a perfect specimen for biomedical research. Yeast are eukaryotic, like all the cells in our body. But yeast also have a few characteristics that bacteria have. Our cells contain all of our genetic code in the nucleus of the cell, making it difficult to harvest. Bacteria contain most of their DNA/RNA inside their nucleus with the exception of a genetic ring in their cytoplasm. Yeast are the only eukaryotic cells know to have this genetic ring as well. That ring allows scientists to take out specific genes and replace them with an artificial genetic code. The scientists then observe how the genetic code affects the cell’s function. Because the yeast is eukaryotic like our cells, the effects it undergoes will be similar to what effects our cells would have undergone. Scientists can also pinpoint which genetic chains cause certain defects.
Yeast is also easy to cultivate in a petri dish since they reproduce quickly. And since yeast infections aren’t fatal there’s little risk in doing research with them.
So the next time you buy a beer, raise a glass to the awesome biological awesomeness that is yeast!