Macromolecules:Carbohydrates

Biochemistry Unit

Structure:

Composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio.

The basic unit is called a monosaccharide and includes glucose, fructose, and galactose.

Monosaccharides are classified by the number of carbon atoms they contain.

Monosaccharide Number of Carbon Atoms

Triose 3

Tetrose 4

Pentose 5

Hexose 6

Structure: Monosaccharide

Monosaccharides contain a hydroxyl functional group and either a ketone or an aldehyde.

Monosaccharides exist as either a long chain or a ring structure.

Structure:Monosaccharide

Most monosaccharides are cyclic when placed in an aqueous solution.

Ring structures vary depending on the location of the hydroxyl group at carbon one (C1).

If the hydroxyl group lies below the ring, then it is α-glucose.

If the hydroxyl group lies below the ring it is β-glucose.

Isomers

The hexose carbohydrates include glucose, galactose, and fructose.

These molecules all have the same chemical formula (C6H12O6), but

their physical arrangement differs. These molecules are isomers.

Disaccharides

Two monosaccharides linked together in a condensation reaction.

The types of monosaccharides that link together will determine the type of disaccharide that forms.

Sucrose = fructose and glucose Maltose = two glucose molecules Remember that with condensation

reactions, a water molecule is also produced during the anabolic chemical reaction.

Disaccharides

The reverse reaction is a hydrolysis reaction and is used to break apart a disaccharide into its monosaccharide components. In a hydrolysis chemical reaction, water is needed to complete the catabolic process.

Polysaccharides

Polysaccharides are composed of hundreds of monosaccharides linked together.

While monosaccharides represent simple sugars, polysaccharides represent complex sugars.

Polysaccharides can exist as long chains or as a long chain with branches. The shape and linkage determines the physical properties of each polysaccharide.

Some biologically important polysaccharides include cellulose and starch which are found only in plants and glycogen which is found in animals. Starch and glycogen are storage molecules and cellulose provides structural support for plants.

Starch: Amylose & Amylopectin

Starch is a main staple for human consumption and is found in potatoes, rice, and wheat.

Starch is the combination of two polysaccharides, amylose, and amylopectin.

Starch: Amylose & Amylopectin

Amylose is a linear chain that is formed by linking the first carbon atom of one α-glucose molecule to the fourth carbon of the second α-glucose molecule (α 1 - 4).

Amylopectin is also composed of α 1 – 4 linkage along its main chain, however, it also contains α 1 – 6 branch.

Cellulose

Cellulose is also found in plants and is formed by excess glucose molecules.

Cellulose provides structural support rather than nourishment for the plant.

Cellulose is a straight chain polymer consisting of β – glucose molecules linked together.

The glycosidic link occurs at the first carbon of one β – glucose molecule and the fourth carbon of the second β – glucose molecule.

Cellulose

The orientation of the glucose molecules created hydrogen bonds between the hydroxyl groups of glucose molecules between two chains of cellulose. This creates strong tough fibres for the cell wall of plants and it also provides industrial use for lumber, paper, and clothing.

Glycogen

Glycogen is a polysaccharide that is only found in animal cells and is generated when there is an excess of glucose in our blood.

The α-glucose molecules are linked in a 1 – 4 arrangement with branches forming at the 1 – 6 linkage.

Similar to amylopectin, there are more branches in glycogen.

Chitin

Cellulose like polymer with a nitrogen containing group attached at C2.

Oligosaccharides

Contain a small number (3-10) of monosaccharides.

Example: a disaccharide is composed of two monosaccharides.

Often found as a component of glycoproteins and glycolipids within cell membranes.