Proteins & Enzymes

Question 1

Explain why enzymes are referred to as biological catalysts

Answer 1

• They increase the rate of reactions in living organisms

Question 2

State the difference between the lock and key model and the induced fit • They increase the rate of reactions in living organisms

Answer 2

• The lock and key model states that the substrate and enzyme are fixed structures that fit perfectly together/ enzyme is rigid and does not change shap
WHEREAS
• The induced fit states that the active site changes shape to fit the substrate

Question 3

Describe the induced fit model

Answer 3

~ Active site not complementary
~ Substrate binds to active site and active site changes shape induced shape on substrate
~ Change in shape puts strain on the bonds, weakening them, so lowers the activation energy
~ Enzyme-product complex forms and the substrate no longer fits so is releases

Question 4

How does a functional protein differ from a polypeptide

Answer 4

•A polypeptide is a long chain of amino acids joined together by peptide bonds
•A functional protein is formed from one or more polypeptide chains
•A functional protein has a specific 3D shape

Question 5

Suggest why a protein can be the substrate for 2 different enzymes

Answer 5

• Different parts of the protein have different amino acid sequences so are a different shape

• Each enzyme has an active site that is a specific shape and complementary to a different part of the protein

Question 6

Describe and explain how you could use the biuret test to distinguish a solution of enzyme lactase from a solution of lactose

Answer 6

• Add biuret reagent to both solutions
• Lactase enzyme will give a purple colour because lactase is a protein

Question 7

Explain how a competitive inhibitor works

Answer 7

1. Inhibitor is a similar shape to substrate;
2. Inhibitor binds to active site of enzyme
3. Less substrate binds/fewer e-s complexes.
   Can be overcome by adding more substrate

Question 8

Explain how a non-competitive inhibitor works

Answer 8

• Inhibitor is not a similar shape to substrate
• Inhibitor enters away from active site/allosteric site
• This changes the shape of the active site
• Less substrate binds- so fewer E-Z complexes formed
Cannot be overcome by adding more substrate

Question 9

An enzyme only catalyses one reaction. Explain why (2)

Answer 9

Enzyme has active site which is a specific shape
Only one substrate binds to active site

Question 10

How does an enzyme-substrate complex increase the rate of reaction

Answer 10

Lowers activation energy by breaking bonds

Question 11

Which substances are formed when two amino acid molecules are joined together

Answer 11

Dipeptide + water

Question 12

Describe how a peptide bond is formed between two amino acids to form a dipeptide

Answer 12

• condensation reaction
• between amine and carboxyl group

Question 13

Two proteins have the same number and type of amino acids but different tertiary structures.

Answer 13

Diff primary structure
Forms ionic/hydrogen/disulphide bonds in different places