Simple sugars - monosaccharides

What are carbon-containing molecules known as?

‘Organic molecules’

Define ‘monomer’

• A single molecule that can chemically bond with other similar molecules to form a polymer

Give 6 examples of monomers

• Monosaccharides

• Amino acids

• Nucleotides

• Phospholipids

• Glycerol

• Fatty acids

Give 4 examples of polymers

• DNA

• Carbohydrates

• Proteins

• Lipids

Define ‘polymer’

• A large molecule made up of many monomers linked together in long chains

Describe monosaccharides

• Simple sugars

• Monomers which join to form more complex carbohydrates e.g disaccharides & polysaccharides

• General formula is (CH2O)n where n is from 3-7

• All monosaccharides & some disaccharides are reducing sugars

• Examples include: glucose, galactose + fructose

What are isomers?

• Molecules that share same molecular formula but have different structural or spacial arrangement of atoms

What are the 2 forms of glucose?

• Alpha & beta - structural forms are known as isomers of glucose

What is glucose also known as?

Hexose sugar (6 carbon atom structure)

Draw alpha glucose

Draw beta glucose

State the function of monosaccharides

• Provide a rapid source of energy. Readily absorbed & require little to no change for use in respiration

State function of glucose

• Cellular fuel: Cells take in glucose & release energy in respiration

• Storage: Extra glucose stored in liver & muscles as glucose so body can use it later when fasting/exercising

State function of galactose

• Mainly in diet as a monomer of a sugar called lactose (disaccharide)

• Energy source & often used in baking products

State function of fructose

• Sugar naturally found in fruit, honey & vegetables - energy source

What’s the difference between alpha glucose & beta glucose?

In α-glucose the OH group is below carbon 1,

in β-glucose the OH group is above carbon 1.

Describe the biochemical test for starch

Add potassium iodide solution.

‣ If starch is present, solution turns from

orange-brown to blue-black.

Describe the biochemical test for a non-reducing sugar

Heat with hydrochloric acid (to hydrolyse any

glycosidic bonds).

‣ Add sodium hydrogen carbonate to neutralise.

‣ Add Benedict’s reagent and heat.

‣ Green/yellow/orange/brick-red precipitate indicates

presence of non-reducing sugar in sample.

‣ Negative result: solution remains blue [sample

contains neither reducing or non-reducing sugars].

Why should an excess of benedict’s reagent be added?

To ensure all the sugars have reacted.