Chemistry Question #315

Navid Patterson, a 16 year old male from the Internet asks on December 24, 1997,

What is sugar?

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The answer

Barry Shell answered on December 24, 1997

Sugar is a carbohydrate, meaning it is made of carbon, hydrogen and oxygen. There are many kinds of sugars. The simplest sugar is glucose with the formula C6H12O6, (6 carbons, 12 hydrogens and 6 oxygen molecules). These are arranged as a chain of 6 carbons. Attached to the first five carbons are OH (hydroxyl groups) and the last carbon has an aldehyde (a double bonded oxygen). Single H atoms hang off the carbons opposite the OH groups. But the direction, order and angles that all these hydroxyl, hydrogens and aldehydes hang off the carbon chain make the difference between glucose and other kinds of simple sugars. For instance, the difference between fructose and glucose is that the aldehyde (the lone oxygen) is attached to the end carbon in glucose but on the second carbon in fructose. All sugar molecules can be right handed or left handed. The right and left handedness is figured out by passing polarized light through a sugar solution and seeing which way the light bends. This handedness is caused, again, by the order and direction and angles that the OH, H and O bits hang off the carbon chain in any particular kind of sugar. By far most naturally occurring sugars ( e.g. sucrose from sugar cane and beets, maltose from grain, and lactose from milk) come as disaccharides, which means they are basically two glucose or fructose molecules joined together. But instead of joining at the ends and becoming a big long 12 carbon chain, they turn into two joined 6-molecule rings containing 5 carbons and one oxygen in each ring. The two rings are hooked together with an oxygen atom. The rings bend up and down in various ways depending on the kind of sugar. It was a Canadian scientist (Raymond Lemieux) who first figured out the exact structure of sucrose, the most common kind of sugar.

Sugar chemistry is really neat because longer chains of sugar - more than two sugar units long - result in cellulose, starch and other polysacharides. Cellulose is one of nature's main building blocks, the single most abundant carbon-containing compound on earth, occurring as the major component of all vegetable matter including wood, cloth, and paper. The other long sugar is starch, which is another very common thing in nature and the major component of most staple foods such as wheat (bread), rice, potatoes, beans, and corn. Another thing about sugar that's interesting is if you leave all this cellulose and starch for several hundred million years compressed and covered under the earth, it turns into oil, coal or natural gas! We're running our cars on hundred million year old sugar. Sugar is nature's number one way for storing solar energy here on earth.

Another incredible fact about sugar is that a type of sugar called deoxyribose sugar is the backbone of a very famous molecule: DNA. This is the molecule that contains the blueprint for making any living thing, including a person like you or me. It seems odd that people should make a big thing about how sugar is bad for us - especially when they say that we should not eat white sugar (sucrose), but should eat fruit sugar (fructose) instead, as if one kind of sugar is ok, but another kind is bad for you. All sugars are practically the same molecule with just tiny differences in shape or order of the OH or O parts. There are enzymes in saliva and all throughout the body that can change these sugars back and forth easily. Admittedly too much of anything is bad for you, including sugar, but the fact is that the whole world runs on one form of sugar or another!

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