2(c) Biological molecules

Biological molecules

Large molecules made up of smaller units

What elements are found in Carbohydrates?

Carbon, Hydrogen, Oxygen

（example of carbohydrates: starch and glycogen=polymers）

What are the subunits/monomers that make up carbohydrates?

Simple sugars

What elements are found in Lipids?

Carbon, Hydrogen, Oxygen

What are the subunits/monomers that make up lipids?

Fatty acids+glycerol

One glycerol is usually joined to 3 fatty acids.

What elements are found in proteins?

Carbon, Hydrogen, Oxygen, Nitrogen (+sulphur)

What are the subunits/monomers that make up proteins?

Amino acids

FOOD TESTS

How do you prepare the food sample?

1. Grind the food with a small quantity of distilled water in a mortar using a pestle.

2. Pour off the liquid into a test tube, leaving any solids behind

How do you test for starch?

Use Iodine!

1. Add 1cm³ of sample solution to a test tube.

2. Using a graduated pipette, add two drops of iodine solution to the food sample. Record any colour change.

3. If starch is present, the solution will turn blue-black. If not, the solution will remain orange.

How do you test for glucose?

1. Add 1 cm³ of sample solution into a test tube.

2. Add an equal volume of Benedict's solution and swirl the mixture.

3. Place it into an electric water bath, temperature set about 80ºC.

4. Leave it for 5 minutes or until the colour no longer changes.

5. If glucose is present, the solution will change from bblue-green-orange-brick-red. If not, the solution remains blue.

What do the colours of the results represent(Benedict's test)?

Blue=no glucose

Green=low concentration of glucose

Orange=medium concentration of glucose

Brick-red=high concentration of glucose

How do you test for Protein?

1. Add 1 cm³ of sample solution into the test tube.

2. Add an equal volume of Biuret's solution to the test tube to mix the contents.

3. Gently shake the tube to mix the contents.

4. If protein is present, the solution will turn lilac/purple. If not, the solution will remain blue.

How do you test for lipids?

1. Add 1cm³ of sample solution into the test tube.

2. Add 2cm³ of ethanol to the sample and gently shake the mixture to mix the contents.

3. Add 2cm³ of distilled water.

4. If lipids are present, a milky-white emulsion will form. If not, the solution will remain clear/transparent/colourless.

Enzymes

Are biological catalysts in metabolic reactions, meaning that they speed up the rate of reaction without being changed or used up

What are enzyms made up of?

Enzymes are proteins made up of chains of amino acids.

How do enzymes work?

Each enzyme has an active site. The shape of substrate is complementary to the shape of active site. When they bind, an enzyme-substrate complex is formed.

What 2 factors affect the rate of enzyme activity?

• Temperature

• pH

What happens to the rate of enzyme activity when the temperature is low?

1. The rate is very slow

2. Molecules have very little kinetic energy and move slower

3. Enzyme and substrate collide less often with each other

4. Less enzyme-substrate complex is formed

What happens to the rate of enzyme activity when the temperature is high?

1. The rate of reaction is fast

2. Molecules have more kinetic energy and move faster

3. Enzyme and substrate collide more often with each other

4. More enzyme-substrate complexes are formed

What happens to the rate of enzyme activity at its optimum temperature?

The rate of reaction is the fastest.

All enzymes have an optimum temperature at which they work the best.

What happens to the rate of enzyme activity above its optimum temperature?

1. Some bonds holding the enzyme together will break, changing the shape of its active site permanently.

2. The substrate no longer fits.

3. The enzyme is denatured.

4. It can no longer catalyse the reaction.

Practical: Investigating how temperature affects enzyme activity

1. Using a pipette, place 1-2 drops of iodine solution into wells of a dimple tile.

2. Add 2cm³ of Amylase to a boiling tube and place it into a water bath with a set temperature(e.g. 20ºC) and wait for 5 minutes.

3. Then add 5cm³ of starch solution to the boiling tube.

4. Add drops of the amylase-starch mixture into a well every 30 seconds, until the colour no longer turns blue-black.

5. Measure the time taken for the reaction to occur.

6. Repeat the whole procedure with different temperatures.

7. Control the concentration or volume of enzyme or substrate.

How does ph affect the rate of enzyme activity?

All enzymes have an optimum pH at which they work the best. It is often neutral pH 7 but not always.

What happens to the rate of enzyme activity when the pH is too high or too low?

1. The pH interferes with the bonds holding the enzyme together, changing the shape of its active site permanently.

2. The substrate no longer fits.

3. The enzyme is denatured.

4. It can no longer catalyse the reaction.