2. proteins and enzymes exam qu

Question 1

explain what causes the secondary structure of a protein to differ from the primary structure (1 mark)

Answer 1

(polypeptide is) coiled/folded

Question 2

explain what is meant by the tertiary structure of a protein (1 mark)

Answer 2

way in which whole molecule is folded
OR
globular shape
OR
folding of secondary structure
OR
structure held by ionic/disulfide bonds

Question 3

explain how heating may affect the tertiary structure of a protein (2 marks)

Answer 3

causes bonds which hold the tertiary structure to break
shape is no longer maintained / protein is denatured

Question 4

explain why trypsin and chmotrypsin break peptide bonds between different amino acids (3 marks)

Answer 4

substrates/active sites with shapes
active site/substrate with complementary shape
fitting/binding to form enzyme-substrate complex

Question 5

describe how you would use a biochemical test to show that a solution contained protein (2 marks)

Answer 5

add biuret’s reagent
turns purple

Question 6

use your knowledge of protein structure to explain why enzymes are specific and may be affected by non-competitive inhibitors (6 marks)

Answer 6

• each enzyme/protein has a specific primary structure/amino acid sequence
• folds in a particular way / has a particular tertiary structure
• active site with unique structure
• shape of active site complimentary to substrate
• inhibitor fits at site other than active site
• determined by shape
• distorts active site
• substrate will no longer fit / form enzyme substrate complexes

Question 7

describe the result you would expect if an enzyme was tested with biuret’s reagent (1 mark)

Answer 7

purple

Question 8

explain why the rate of reaction would change if the temperature fell by 10 degrees (3 marks)

Answer 8

molecules would have less kinetic energy
fewer collisions
less enzyme-substrate complexes formed

Question 9

explain why the rate of reaction would change if the pH changed substantially (3 marks)

Answer 9

change in pH alters shape
distorts active site / shape of tertiary structure
substrate will no longer fit to active site

Question 10

explain why proteins are polymers (1 mark)

Answer 10

made up of many monomers/amino acids

Question 11

explain what causes molecules of a particular protein always to fold into the same shape (2 marks)

Answer 11

protein has primary structure / amino acid sequence
therefore bonds always form in same position

Question 12

describe how molecular shape is important in explaining the way in which enzymes may be affected by inhibitors (6 marks)

Answer 12

• active site (of enzyme) has particular shape
• (into which) substrate molecule fits / binds
• appropriate reference linking induced fit and shape
• (competitive inhibitor) has similar shape to substrate
• also fits active sites
• prevents substrate access
• (non-competitive inhibitor) fits at site other than active site
• distorting shape of active site / enzyme
• prevents substrate access (award once only)
• two types identified as competitive and non-competitive