Carbohydrates Only 3 elements – carbon,

hydrogen and oxygen

glucose

Glucose is a monosaccharide

This means that it is the smallest unit of sugar – a single sugar molecule.

Glucose has a ring structure with a single oxygen (red) in the ring.

The Carbon atoms are numbered 1 to 6 (black)

The chemical formula for glucose is;

C6H12O6

With equal numbers of Carbon (C) and water (H2O)

This molecule is a carbohydrate.

To simplify this diagram, biologists use a shorthand sketch to represent glucose.

The sketch shows lines between the carbons and the important oxygen molecule in the ring.

When glucose is heated to above 80°C – the bond on the oxygen within the ring will break.

This heating gives a linear molecule.

Benedict’s reagent will bind to the double bonded oxygen – causing a colour change.

Two types of Glucose

Both types of glucose have a hydroxyl group on one side at carbon 4. This is a reactive chemical group.

Two types of Glucose

Alpha Glucose…

…has a hydroxyl on carbon 1 which is turned upwards.

Beta Glucose…

…has a hydroxyl on carbon 1 which is turned downwards.

Two types of Glucose

α Glucose… β Glucose…

This affects the way glucose molecules bond to each other.

C4 C1 C4 C1

4 1 4 1

Monosaccharides are bonded by enzymes. It is the hydroxyls on Carbon 1 and Carbon 4 that are reacted to join the molecules.

The enzymes remove water from the bond, leaving a single oxygen. This is a condensation reaction.

H2O

Removing water to join molecules is called a condensation reaction.

Water is condensed out, in the reaction.

If you are a chemistry student, you will know that removing water to join any molecules is referred to as a condensation.

4 1 4 1

Monosaccharides are bonded by enzymes. It is the hydroxyls on Carbon 1 and Carbon 4 that are reacted to join the molecules.

This bond is called a 1,4,glycosidic bond.

H2OThis forms maltose – a disaccharide.

maltose

Hydrolysis

Two glucose molecules that are joined by a glycosidic bond are referred to as a disaccharide.

Such molecules can be split by enzymes - water is added to the glycosidic bond

Adding water is called hydrolysis (chemists should know that adding water to split non-biological molecules has a different terminology in chemistry)

Challenge!

Can you draw a maltose molecule and show how it can be split using a hydrolysis reaction?

Don’t use the text book!

Polysaccharides = many ……………… joined by ……………

bonds

• They are large insoluble molecules

• They are either used for storage (………. in plants and ………….. in animals)

• Or they are used to form ………………… in plants (……………..)

Polysaccharides = many monosaccharides joined by

glycosidic bonds

• They are large insoluble molecules

• They are either used for storage (starch in plants and glycogen in animals)

• Or they are used to form cell walls in plants (cellulose)

Starch – a compact polymer of alpha glucose in plants

Glycogen – a compact polymer of alpha glucose in animals

Cellulose - a fibrous / linear polymer of beta glucose in plants

Carbohydrates:- if these are the answers, what are the questions?

1) glycosidic bond2) beta glucose3) carbon, hydrogen and oxygen4) insoluble, compact, hydrolysed to alpha glucose5) insoluble, linear, strong, difficult for mammals

to digest6) sucrose7) brown to black8) blue solution to red precipitate 9) water forms and a bond is made10) many weak hydrogen bonds

Brain warm-up Can you explain these words?

α glucose reducing sugar

β glucose glycosidic bond

monosaccharide/ disaccharide monomer

condensation hydrolysisreaction reaction