Carbohydrates Properties Controlled by Structure

What is a Carbohydrate? Carbohydrates are energy-rich organic compounds that contain the elements carbon, hydrogen, and oxygen. Carbo- stands for carbon and hydrate for water, which contains hydrogen and oxygen. Simple carbohydrates are sugars; there are many different kinds of sugars. Some can bought in boxes from the grocery store, but many are also present naturally in foods such as fruits and milk. One of the simplest but most important carbohydrates in your body is glucose. Several other carbohydrates are isomers of glucose.

What is an Isomer? Two compounds that have the same molecular formula, but have different structural formulas are called isomers. Isomers have different properties even though they have the same number and types of atoms. It is the structural formula that determines the properties of each isomer.

Isomer Examples – Butane & Isobutane Boiling Point Melting Point o o -138 C 0 C o -160 C o -12 C

Simple Carbohydrates – Not so simple The molecular formula shows the numbers of each atom that make up the molecule and for glucose it is: C6H12O6 The structural formula for glucose shows how the atoms are arranged: Carbohydrates with only one carbon ring are called monosaccharides

Simple Carbohydrate Isomers Some carbohydrates have the same molecular formula as glucose, but a different structure: These are also known as isomers.

Simple Carbohydrate Isomers Sometimes the structural formulas of two isomers have very small differences as in glucose and galactose: OH is up OH is down

Properties Depend on Structure Glucose is present in human blood, where it is used to form other molecules needed by the body. Fructose appears in sweet fruits along with glucose. Galactose is found in combination with other carbohydrates in human nerve tissue. Nature can detect the small structural changes among the various isomers and use each one for a specific function.

Other “Simple” Carbohydrates Glucose and fructose combine to form sucrose, common table sugar: Sucrose has two carbon rings, so it is called a disaccharide.

Complex Carbohydrates A complex carbohydrate is made of a long chain (a polymer) of simple carbohydrates (monomers) bonded to each other. Starch, cellulose and glycogen are all built from glucose monomers, but the monomers are arranged differently in each case. Starch and cellulose are found in plants, while glycogen is present in liver and muscle cells. Complex carbohydrates have many carbon rings, so they are called polysaccharides.

Different Polymers from Glucose Plants, Trees, Fruits, Vegetables Plants, Trees, Fruits, Vegetables Glucose Cellulose Glucose Straight Polymer Chain Backbone Cellulose Animal & Human Liver & Muscles Animal & Human Liver & Muscles Branched Polymer Chain Backbone Glycogen Glycogen