|MadSci Network: General Biology|
Life at any level (in the cells of our bodies, or inside of bacteria) is an incredibly complex soup. The things we eat, or the things that bacteria live on, get digested, absorbed into cells, and converted to whatever the cell needs. The conversions (what gets turned into what) are governed by protein molecules called "enzymes." There needs to be at least one enzyme — sometimes several — to control formation of every substance that makes up a cell; and there are many, many substances. Most of the information in our chromosomes (and in bacterial chromosomes) is about which enzymes the cell can produce. Most of the key enzymes in the human body work best at body temperature — 98.6 F. Bacterial enzymes have different temperature preferences: the bacteria that make us sick have enzymes that work best at body temperature and may even work OK when our body temperature goes up (fever). Most bacteria that spoil food have enzymes that work best in the range from room temperature to body temperature. These enzymes may also work in the refrigerator, but their action is slower. These bacteria break down food for a living; they can usually still multiply in the fridge, but their enzymes don't break the food down as fast. Most enzymes in our bodies' cells won't work at all at refrigerator temperatures. Many molds can also make enzymes that break down food at refrigeration temperature; molds also need air. When you buy food in a vacuum or controlled-atmosphere package, the lack of oxygen keeps molds from growing on the food in the refrigerator. When we put leftovers in the fridge, we usually try to seal the container, which can help slow down molds by excluding air. However, things still get moldy in the refrigerator unless they stay sealed in the original package. All the same, everything spoils eventually at refrigeration temperatures because the enzymes, whether from bacteria or molds, slowly break the food down. Life stops in the frozen state, so things in the freezer don't spoil. Food in cans (the kind that don't say "keep refrigerated") has been heated to a high enough temperature to kill molds, bacteria, and all of their enzymes, so canned foods don't spoil, either.
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