Urea is a small molecule formed as proteins are broken down. It’s excreted in urine, but isn’t particularly toxic at low levels so it’s found in cells throughout the body. The molecular structure of urea is below, and as it contains nitrogen (N) several pathogens have adapted to use it as a nitrogen source using an enzyme called urease to break it down.
The urease converts urea into ammonia and carbamic acid, which then spontaneously reacts with water to form carbonic acid (and produces another ammonia). Converting the carbonic acid into bicarbonate produces a buffer solution: the ammonia and bicarbonate can bond with and dissociate from free hydrogen ions enough to keep the pH of the surrounding area relatively neutral. This is particularly useful for bacteria such as Helicobacter pylori which colonises the stomach and therefore needs to cope with very acidic conditions.
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