Enzymes I

Question 1

what is the role of enzymes?

Answer 1

to catalyse specific chemical reactions

eg blood clotting, nerve conduction

Question 2

what can enzyme defects lead to?

Answer 2

disease

eg glycogen storage disease

Question 3

how are enzymes utilised?

Answer 3

they are targets for therapeutic drugs

• antibiotics inhibit enzymes
• anti inflammatory agents
• anti cancer drugs

Question 4

what are the properties of enzymes?

Answer 4

• increase rate of reaction by 10 billion folds
• shows specificity
• unchanged at end of reaction
• does not alter reaction eqm
• lowers activation energy so less ΔG required

Question 5

describe the structure and function of active sites

Answer 5

• 3D cavity/cleft that binds to substrate w specificity through hydrophobic, H, electrostatic bonding and van de waal forces
• formation of ES complex is first step of enzyme catalysis
• seen through x ray crystallography and kinetic studies of enzymes

Question 6

what is the michaelis constant?

Answer 6

measures the enzyme substrate affinity

-Vmax/2

Question 7

what is Vmax?

Answer 7

the maximum velocity of saturation at the active sites

Question 8

what is the michaelis-menton equation?

Answer 8

V = Vmax + ([S]/ ([S] + Km))

• will give a exponential graph

Question 9

what is the double reciprocal plot?

Answer 9

1/V = 1/Vmax + ((Km/Vmax) x (1/[S]))

• gives a linear graph

Question 10

What is the turnover number?

Answer 10

• max number of substrate molecules handled per active site
• also called Kcat:

Vmax/[enzyme]

Question 11

what is a competitive inhibitor?

Answer 11

molecule that competes with substrate by binding to the active site of the enzyme

Question 12

what happens in the presence of a competitive inhibitor?

Answer 12

• Km increases
• more substrate required to reach Km
• Vmax stays same

Question 13

what is a non competitive inhibitor

Answer 13

a molecule that binds to a different site to the active site

• causes a conformation on enzyme
• Vmax reduced but Km stays same

Question 14

how is enzyme activity regulated?

Answer 14

• control of gene expression
• compartimentation: sequence of enzyme polypeptide chain target enzyme to ER to ensure that enzyme activity occurs in particular part of cell
• allosteric regulation: regulatory molecule causes conformational change to reduce enzyme activity
• covalent modification of an enzyme: changes enzyme shape