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Monday, August 24, 2009

Sugars and Carbohydrates

I've pointed you to the excellent articles on Medical News Today, especially those written by Christian Nordqvist before, in fact just a month ago with All About Diarrhea.

Here's yet another excellent summary, on carbohydrates and sugars.
Again, the article is much too long to summarize and is well worth reading. I just want to excerpt the section explaining the types of sugars themselves, something of particular interest to those of us who have problems digesting disaccharides into monosaccharides.

What are saccharides?

Saccharides, or carbohydrates, are sugars or starches. Saccharides consist of two basic compounds:

Aldehydes - composed of double-bonded carbon and oxygen atoms, plus a hydrogen atom.

Ketones - composed of double-bonded carbon and oxygen atoms, plus two additional carbon atoms.

There are various types of saccharides:

Monosaccharide - this is the smallest possible sugar unit. Examples include glucose, galactose or fructose. When we talk about blood sugar we are referring to glucose in the blood; glucose is a major source of energy for a cell. In human nutrition, galactose can be found most readily in milk and dairy products, while fructose is found mostly in vegetables and fruit.

When monosaccharides merge together in linked groups they are known as polysaccharides.

Disaccharide - two monosaccharide molecules bonded together. Disaccharides are polysaccharides - "poly…" specifies any number higher than one, while "di…" specifies exactly two. Examples of disaccharides include lactose, maltose, and sucrose. If you bond one glucose molecule with a fructose molecule you get a sucrose molecule.

Sucrose is found in table sugar, and is often formed as a result of photosynthesis (sunlight absorbed by chlorophyll reacting with other compounds in plants). If you bond one glucose molecule with a galactose molecule you get lactose, which is commonly found in milk.

Polysaccharide - a chain of two or more monosaccharides. The chain may be branched (molecule is like a tree with branches and twigs) or unbranched (molecule is a straight line with no twigs). Polysaccharide molecule chains may be made up of hundreds or thousands of monosaccharides.

Polysaccharides are polymers. A simple compound is a monomer, while a complex compound is a polymer which is made of two or more monomers. In biology, when we talk about building blocks, we are usually talking about monomers.

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