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Chemical Properties of Carbohydrates

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Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

Carbohydrates, the human body's main energy source, can be analyzed through their chemical properties. Learn about the structure of carbohydrate molecules, the differences between monosaccharides and polysaccharides, their atomic composition, and how they react with water. Updated: 12/14/2021

General Structure of Carbohydrates

Despite having a bad reputation lately, carbohydrates are the body's main source of energy. Human beings cannot function without carbohydrates. Glucose, a simple sugar, is essential for cells to function. A diet without carbohydrates can force the body to break down proteins and fats for energy, which may cause harm. The word carbohydrate tells us exactly what they are made from. 'Carbo' refers to carbon, and 'hydrate' refers to water.

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  • 0:00 General Structure of…
  • 0:32 Monosaccharides
  • 1:23 Polysaccharides
  • 2:59 Carbohydrates and Water
  • 3:39 Lesson Summary
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The simplest carbohydrates are called monosaccharides. 'Mono' means one, and 'saccharide' means sugar. These are, therefore, single molecules of sugar. Some common examples include glucose, fructose, and galactose. Monosaccharides can have either a linear structure, meaning they are arranged in a straight line, or have a ring structure, meaning they close up like a circle.

An interesting fact about monosaccharides is that different monosaccharides can be made from the same elements. For example, glucose, fructose, and galactose are all made from 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. However, they are different sugars, because the atoms are arranged in slightly different ways. Another way to describe this is to say that they are isomers.


Polysaccharides are more complex carbohydrates. The smallest of the polysaccharides are the disaccharides, which are made from two monosaccharides joined together. An example is sugar lactose, which is a disaccharide of glucose and galactose. Generally, though, the term polysaccharide refers to a carbohydrate that has many, many monosaccharides joined together ('poly' means many).

Starch is the simplest of the complex carbohydrates. Starch is used to store energy in plant cells. It is made of a simple chain of monosaccharides joined together. Because it is so simple, it is very easy to break apart the monosaccharide molecules to get energy.

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