biological molecules (chapter 3)

carbohydrates definition

Carbohydrates are organic molecules made up of the elements carbon, hydrogen and oxygen. The hydrogen and oxygen atoms are present in the ratio 1:2

single sugars

• glucose → found in plants and animals

• fructose→common in plants but rare in humans

double sugars

• maltose = glucose +glucose

• sucrose = glucose +fructose

how can we test for reducing sugars

1. place 2cm3 of each food sample into a test-tube

2. Add 2cm3 of Benedicts solution to the food sample

3. Shake the mixture and place the test-tube in a boiling water-bath for 2-3 minutes

4. record the color of the solution

OBSERVATIONS:

• solution remains blue→ no reducing sugar

• turned from blue to green → traces of reducing sugar

• turned from blue to yellow/orange → moderate amount of reducing sugars

• turned from blue to red/ Red precipitate formed → large amount if reducing sugars

complex carbohydrates

1. STARCH → made up of several thousand glucose molecules joined together → storage form of carbohydrates in plants. can be digested to glucose to provide energy for cell activities . → found in storage organs of plants

2. CELLULOSE → made up of many glucose molecules joined together. The bonds between the glucose units are different from that in starch → found in cell walls which protect plants cells from bursting or damage. Cellulose cannot be digested in our intestines.

3. GLYCOGEN→ branched molecules, made up of many glucose molecules joined together. → storage form of carbohydrates in mammals, digested to glucose to provide energy for cell activities → stored in the liver and muscles of mammals.

breakdown of starch

• enzyme amylase digests starch to form sugar maltose .

• amylase CANNOT breakdown maltose to glucose.

• Maltose is hydrolysed to glucose by MALTASE.

fats definition

Fats are organic molecules made up of elements carbon, hydrogen and oxygen. Fats contains much less oxygen in proportion to hydrogen

Breakdown of Fats

Fat molecule ——> (lipase enzyme) glycerol+ three fatty acid molecules

Test for fats

Samples in liquid state

1. Add 2cm3 of ethanol to a drop of liquid sample in a test-tube and shake the mixture thoroughly.

Add 2cm3 of water to the mixture and shake the mixture

Samples in solid state

1. Crush the solid sample into smaller pieces using a mortar and pestle and place the pieces in a test-tube.

2. Add 2cm3 i of ethanol into the test-tube and shake throughly.

3. Allow the solid particles to settle. Carefully decant the ethanol into another test-tube containing 2cm3 of water and shake the mixture.

OBSERVATIONS:

• The white emulsion produced indicates the presence of fats

Proteins definition

Proteins are organic molecules made up of the elements carbon, hydrogen, oxygen and nitrogen. Sulfur MAY be presen

Test for proteins

1. To 2cm3 of liquid food sample, add an equal amount of biuret solution

shake well and allow the mixture to stand for 5 minutes

OBSERVATIONS:

• a violet colour indicates the presence of proteins