FHMP 011 Enzymes and catalysis

Question 1

What is an enzyme?

Answer 1

biological catalyst

Question 2

What is Vmax of an enzyme?

Answer 2

The maximum rate of reaction or the rate of reaction under ideal circumstances

Question 3

What is Kcat?

Answer 3

• the turnover number
• Vmax/[E]
• the number of substrate molecules converted into product by an enzyme molecule in a second when the enzyme is fully saturated with substrate

Question 4

What is Km?

Answer 4

Substrate concentration at 1/2 Vmax

Question 5

what 3 factors make enzymes good catalysts?

Answer 5

• activity at low temps
• specificity towards substrate
• specificity of reaction

Question 6

what is a cofactor?

Answer 6

something that an enzyme requires to increase their activity/efficiency

Question 7

give 3 types of cofactors

Answer 7

• metal = e.g. magnesium
• prosthetic group = bound to enzyme e.g. FAD
• coenzymes = e.g. ATP

Question 8

what is the EC number?

Answer 8

• way of classifying enzymes based on the type of reaction it catalyses
• e.g. 1,2,3,4,5,6

Question 9

what does EC number 1 mean?

Answer 9

1 = oxidoreductases = redox reactions = e.g. lactate dehydrogenase

Question 10

what does EC number 2 mean?

Answer 10

2 = transferase = group transfer reactions e.g. DNA methyltransferase

Question 11

what does EC number 3 mean?

Answer 11

3 = hydrolyses = hydrolysis reactions e.g. chymotrypsin

Question 12

what does EC number 4 mean?

Answer 12

4 = lyases = addition/removal of groups to form double bonds e.g. lyases

Question 13

what does EC number 5 mean?

Answer 13

5 = isomerases = isomerisation e.g. triose phophate isomerase

Question 14

what does EC number 6 mean?

Answer 14

6 = ligases = ligation of 2 substrates at the expense of ATP hydrolysis e.g. aminoacyl-tRNA synthase

Question 15

what is the active site?

Answer 15

The active site is the region on the enzyme where the substrate binds.

Question 16

what factors affect enzyme activity?

Answer 16

temperature, pH, substrate and enzyme concentration

Question 17

describe how pH effects enzyme activity

Answer 17

• every enzyme will have its specific optimum pH range
• the pH if outside the optimum range, the H+ or OH- ions will interact with the enzyme’s structure, thus effecting its binding ability and decreasing its activity outside the range ( enzyme denatures)

Question 18

describe how temperature effects enzyme activity

Answer 18

• as temperature increases, they gain more energy and collide more often and increasing the activity until it reaches its optimum temperature
• when the enzyme reaches past its optimum temperature, the bonds of the enzyme will start to break down and the structure which effects its binding ability and thus decreases its activity (enzyme denatures)

Question 19

what does thermolabile mean?

Answer 19

• a substance that is easily destroyed or denatured by heat

- mutations in an enzyme can make it more sensitive to temperature change

Question 20

How does enzyme concentration affect enzyme activity?

Answer 20

• increasing the enzyme concentration increases the rate of reaction as it increases the availability of the active sites
• the substrate conc is the limiting factor

Question 21

How does substrate concentration affect enzyme activity?

Answer 21

• increasing the substrate conc increases the rate of reactions as more substrate can bind to the enzymes
• the enzyme conc is the limiting factor

Question 22

What is an isozyme?

Answer 22

Enzymes that catalyze the same reaction but have different chemical composition and different physical properties

Question 23

give an example of isozymes

Answer 23

• lipoprotein lipase = adipose and muscle have different isozymes of this enzyme
• adipose = rate of fatty acid release is dependant on lipoprotein levels, has a high Km, after a meal when there is high lipoprotein levels, adipose LPL is highly active
• muscle = rate of fatty acid release is dependant on LPL conc as it has a low Km, so it is saturated at high lipoprotein levels, after meal, activity does not increase as already saturated
• or glucokinase/hexokinase

Question 24

What is cooperativity?

Answer 24

a form of allosteric regulation that can amplify or decrease enzyme activity

Question 25

what is negative cooperativity?

Answer 25

• binding of one molecules decreases the affinity for binding the others, at high substrate concentrations, the enzyme is inhibited
• decreases the activity of the enzyme

Question 26

what is positive cooperativity?

Answer 26

• First binding event increases affinity at remaining sites
• at high substrate concentration, the enzyme activity increases
• increase activity of the enzyme