Biological molecules

Question 1

What are the chemical elements found in carbohyrates?

Answer 1

carbon, hydrogen, oxygen

Question 2

What are the chemical elements found in proteins?

Answer 2

carbon, hydrogen, oxygen, nitrogen

Question 3

What are the chemical elements found in lipids?

Answer 3

carbon, hydrogen, oxygen

Question 4

Describe the structure of carbohydrates as a large molecule made up from smaller basic units

Answer 4

starch and glycogen are large complex carbohydrates, made of of many smaller units (eg glucose, maltose) joined together in a chain

Question 5

Describe the structure of proteins as a large molecule made up from smaller basic units

Answer 5

proteins are made up of long chains of amino acids

Question 6

Describe the structure of lipids as a large molecule made up from smaller basic units

Answer 6

lipids (fats and oils) are built from fatty acids and glycerol

Question 7

Describe the food test to identify the presence of glucose

Answer 7

1. prepare a food sample and add 5cm3 to a test tube
2. prepare a water bath at 80°C
3. add 10 drops of benedicts solution to the test tube
4. leave the test tube in the water bath for 5mins
   * blue (no change) = no glucose
   * green / yellow = low concentration
   * brick red = high concentration

Question 8

Describe the food test to identify the presence of starch

Answer 8

1. prepare a food sample and put 5cm3 in a test tube
2. add 5 drops of iodine solution
   * brown / orange (no change) = no starch
   * blue / black = starch present

Question 9

Describe the food test to identify the presence of proteins

Answer 9

1. prepare a food sample and add 5cm3 to a test tube
2. add 5cm3 of biruet solution
   * blue (no change) = no protein
   * pink / purple = protein present

Question 10

Describe the food test to identify the presence of lipids (fats)

Answer 10

1. prepare a food sample and add 5cm3 to a test tube
2. add ethanol and water to substance
   * no change = no lipids
   * white cloudy suspension = lipids present

Question 11

What are the roles of enzymes as biological catalysts in metabolic reactions?

Answer 11

• proteins which catalyse reactions without being changed
• digestion - breaks down a large substance into smaller molecules
• synthesis - helps smaller chemicals join together to make larger ones

Question 12

Explain how temperature can affect enzyme function

Answer 12

• temperature too low - less kinetic energy so less collisions, slower reaction rate
• all enzymes have an optimum temperature
• temperature too high - enzyme denatures (changes shape of active site)
• changes shape because the bonds holding the enzyme together break
• substrate cannot fit anymore so rate of reaction decreases rapidy and stops
• denaturing is irreversible

Question 13

How does pH affect enzyme function?

Answer 13

• pH can interfere with the bonds holding the enzyme together if too high or too low, which changes the shape of the active site - denatures the enzyme
• all enzymes have an optimum pH, often 7, but not always