Biological molecules

State the chemical elements present in carbohydrates, lipids and proteins 3.

Carbohydrates contain carbon, hydrogen and oxygen.

Lipids contain carbon, hydrogen and oxygen.

Proteins contain carbon, hydrogen, oxygen and nitrogen.

Describe two differences between carbohydrates and lipids 4.

• Carbohydrates are made from sugars,

• whereas lipids are made from fatty acids and glycerol.

• Carbohydrates are used for short-term energy,

• whereas lipids are used for long-term energy storage.

Describe the structure of starch and glycogen 4.

• Both starch and glycogen are large molecules (polymers)

• made from many glucose molecules.

• Starch consists of long chains of glucose,

• while glycogen is highly branched.

Proteins are polymers. Explain what this means 1.

• Proteins are large molecules made from smaller subunits called amino acids.

Describe how a lipid molecule is formed 1.

• A lipid molecule is formed from one glycerol molecule joined to three fatty acid molecules.

Describe how to test a food sample for glucose and state the positive result 4.

• Add Benedict’s solution to the food sample and

• heat it in a water bath.

• A colour change from blue to orange or brick-red

• shows glucose is present.

What reagent is used to test for starch and what is the positive result 2.

• Iodine solution is used and a colour change from

• orange-brown to blue-black shows starch is present.

Describe the test for protein 4.

• Add Biuret solution to the food sample.

• No heating is required.

• A colour change from blue to purple or lilac

• shows protein is present.

Describe the ethanol emulsion test for fat

• Add ethanol to the food sample and shake,

• then add water.

• A white or milky emulsion shows fat is present.

Explain why a water bath is used instead of a Bunsen burner in the Benedict’s test 1.

• A water bath is safer,

• prevents direct heating,

• controls temperature and

• reduces the risk of fire.

Define an enzyme 1.

• An enzyme is a protein that

• acts as a biological catalyst and

• speeds up chemical reactions without being used up.

Explain why enzymes are specific 4.

• Enzymes have an active site

• with a specific shape.

• Only one substrate fits,

• forming an enzyme-substrate complex.

Describe the lock-and-key model of enzyme action 3.

• The substrate fits exactly into the enzyme’s active site

• like a key in a lock.

• The reaction occurs and products are released.

Describe and explain the effect of increasing temperature on enzyme activity 6.

• Enzyme activity increases at first

• because molecules have more kinetic energy and

• collide more often.

• At high temperatures the enzyme denatures,

• the active site changes shape and activity decreases.

What does it mean when an enzyme is denatured 2.

• The active site of the enzyme changes shape

• so the substrate can no longer bind.

Describe an experiment to investigate the effect of temperature on enzyme activity 6.

• Use an enzyme and a substrate

• Use water baths at different temperatures

• Keep pH constant

• Keep enzyme concentration constant

• Measure the rate of reaction

• Repeat for reliability

Explain how changes in pH affect enzyme activity 4.

• Each enzyme has an optimum pH

• Changes in pH affect bonds in the enzyme

• Active site shape changes

• Extreme pH causes denaturation

Describe how you would investigate the effect of pH on enzyme activity 6.

• Use buffer solutions of different pH

• Use the same enzyme and substrate

• Keep temperature constant

• Measure rate of reaction

• Record results

• Repeat and calculate a mean

State three variables that should be controlled in enzyme experiments 3.

• Temperature

• pH

• Enzyme concentration or substrate concentration

An enzyme works fastest at pH 7. Explain why activity decreases on either side 4.

• pH affects the enzyme’s structure

• Bonds holding the enzyme change

• Active site shape changes

• Fewer enzyme-substrate complexes form

An enzyme breaks down 60 molecules in 2 minutes. Calculate the rate per minute 3.

• Correct calculation method shown

• 60 divided by 2

• Rate is 30 molecules per minute

Give two advantages of enzyme-controlled reactions 4.

• Faster reaction rates

• Work at low temperatures

• Energy efficient

• Highly specific

Explain why digestive enzymes are important in humans. 5.

• Break down large molecules

• Into small soluble molecules

• Allow absorption into the bloodstream

• Provide energy

• Used for growth and repair

An enzyme is heated to 80°C and then cooled but no longer works. Explain why. 6.

• High temperature denatures the enzyme

• Bonds in the enzyme break

• Active site changes shape

• Substrate no longer fits

• Denaturation is permanent

• Cooling does not restore shape

Describe the structure and function of carbohydrates, proteins and lipids 6.

• Carbohydrates are made of sugars

• Used as an energy source

• Proteins are made of amino acids

• Proteins act as enzymes or structural molecules

• Lipids are made of fatty acids and glycerol

• Lipids store energy long-term