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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.
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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.
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Isomer Examples – Butane & Isobutane
Melting Point
-138 oC
-160 oC
Boiling Point
0 oC
-12 oC
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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
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Simple Carbohydrate Isomers
Some carbohydrates have the same molecular
formula as glucose, but a different structure:
These are also known as isomers.
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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
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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.
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Other “Simple” Carbohydrates
Glucose and fructose combine to form sucrose,
common table sugar:
Sucrose has two carbon rings, so it is called a disaccharide.
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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.
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Plants, Trees,
Different Polymers from Glucose
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
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