A monosaccharide is a type of sugar that can't be broken down further. It is the simplest of the simple sugars, with just one sugar molecule or saccharide—hence "mono." These sugars are, for the most part, carbohydrates, and they have an interesting role in the body.
Monosaccharides are rapidly absorbed thanks to their uncomplicated structures, so they're often a quick source of energy. But a diet comprising too many simple sugars is comes with a risk for chronic disease. There is a lot to learn about these interesting compounds.
Monosaccharides comprise carbon, hydrogen, and oxygen atoms. Hydrogen and oxygen make water, which is how carbohydrates get their name. Monosaccharides have the same number of carbon and oxygen atoms and twice as many hydrogen atoms. They are subcategorized depending on the number of carbon atoms, and the number of hydrogen atoms changes accordingly.
For instance, three carbon atoms are present in the monosaccharide triose.
Glucose is an important monosaccharide. It's a six-carbon sugar. Galactose forms part of lactose, and it's another oft-discussed monosaccharide. Lactose is the sugar in milk that can cause digestive distress and has led to a spate of lactose-free products for the intolerant.
A third common monosaccharide is fructose, which you may recognize as the sugar in fruit.
All monosaccharides contain a carbon chain, and each carbon on the chain bonds to an oxygen with a single or double bond. Only one carbon atom has a double bond to the oxygen; the rest all have single bonds. Where the double bond is placed determines whether there's an aldehyde or a ketone. Aldehydes are often toxic in the body, while ketones are the acids your body makes as you break down fats (think ketosis).
Monosaccharide isomers with the same formula but different structures have different biological functions. Organisms use glucose, galactose, and fructose, for example, for energy. Just how much these compounds can vary in their function, though, is clear when you look at xylose, a monosaccharide that combines with xylan to form tree wood.
Another monosaccharide, deoxyribose, puts the D in DNA, the building blocks of life.
Vitamin C is a monosaccharide derivative of glucose. Glucosamine is an amino sugar, and it also derives from glucose. It has the task of producing connective tissue, cartilage, and the chitin that makes up arthropod exoskeletons and fungi cell walls.
Sweeteners can also come from monosaccharides, perhaps unsurprisingly. Mannitol, for instance, is derived from mannose.
Disaccharides (like granulated sugar) and polysaccharides are broken down into monosaccharides during digestion. Sugar tastes so good, which is why it's such a big player in the Standard American Diet (SAD), and too much sugar can lead to obesity and other health issues.
However, it's a misconception that you need to, for example, eliminate fructose-containing fruit from your diet when you want to lose weight. Rather, like so many things we eat, we should aim to consume natural sugars in moderation; fats aren't evil, and nor is the humble monosaccharide.
You'll hear a lot about simple carbs versus complex carbs in discussions about optimal nutrition. What's the difference? Well, the former refers to monosaccharides and disaccharides with one or two sugar molecules. Complex carbs, on the other hand, have three or more sugar molecules and are considered low GI. They raise blood glucose levels for longer and sustain energy. They're also more nutritious because they tend to be higher in fiber, so they digest more slowly, giving the body time to extract lots of nutrients from its food.
Inexpensive polysaccharides can produce various hexoses, a type of monosaccharide, for application in the food industry. These hexoses are used in dietary supplements, beverages, and processed foods, for example.
Carbohydrates are a macronutrient alongside fat and protein. All carbs are made from monosaccharides, but not all monosaccharides are carbs. Monosaccharides are water-soluble crystalline solids, and their OH group orientation interacts with our sweet taste buds.
Monosaccharides are a foundation for more complex molecules. They can't be broken down further and are thus referred to as simple sugars. Monosaccharides store energy and give shape to much of the natural world. In total, there are nine common monosaccharides, including glucose, fructose, galactose, and ribose.
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