Molecular Biology - Saccharides 

Monosachharide #1 - Glucose

• Glucose has the formula C6H12O6
• It forms a hexagonal ring (hexose)
• Glucose is the form of sugar that fuels respiration
• Glucose forms the base unit of many polymers

Monosaccharide #2 - Glactose

• Glactose is also a hexose sugar
• It has the same formula C6H12O6 but is less sweet
• Most commonly found in milk but also cereals

Monosaccharide #3 - Fructose

• Fructose is another pentose sugar
• Commonly found in fruits and honey
• Sweetest naturally occurring carbohydrate

Monosaccharide #4 - Ribose

• Ribose is a pentose sugar
• Forms the backbone of RNA
• Deoxyribose – 2nd carbon is deoxygenated – forms backbone of DNA

Monosaccharides (sugars) are the monomers of polysaccharides (carbohydrates):

Disaccharide #1 - Maltose

• Maltose (C12H22O11) is a dimer of glucose)
• Double the formula and ge rid of a water molecule

Disaccharide #2 - Lactose

• Lactose (C12H22O11) is most commonly found in milk
• The two subunits that make up lactose are glucose and galactose

Disaccharide #3 - Sucrose

• Sucrose (C12H22O11) is also known as table salt
• Two monosaccharides that make it up are glucose and fructose

Polysaccharides (such as glucose) are polymers more than two molecules

• Starch, cellulose, glycogen
• Starch and glycogen have a 1-4 bond (straight chains)

Polysaccharides #1 - Cellulose

• Cellulose made from beta glucose molecules
• Condensation reactions link carbon atom 1 to carbon atom 4 on the next beta glucose
• Glucose subinite=s in the chaina re oriented alternately upwards and downwards
• This makes is a straight chain
• Cellulose molecules are unbranched chains of beta glucose
• Hydrogen bonds link the molecules together
• The linked molecules form bundles called cellulose microfibrils
• They have high tensile strength.

Polysaccharide #2 - Starch

• Amylose and amylopectin are both forms of starch and made from repeating glucose units
• Amylose – the chain of alpha glucose molecules un branched and forms helix
• Amylopectin the chain is branches so has a more globular shape
• Starch is only made my plant celss
• Molecules of both types of starch ar hydrophilic but are too large to be soluble In water
• Starch does not affect osmotic balance of cells
• It is easy to add or remove extra glucoe molecules to starch

Polysaccharide #3 - Glycogen

• Glycogen (C6H10O5) is a polymer made from repeating glucose subunits
• It branches many times
• Condensation reaction link carbon atom 1-4 on the next alpha glucose
• Store glucose as glycogen so we can break it down later