Enzyme Properties, Kinetics and Regulation

Question 1

What are Enzymes?

Answer 1

They are biological catalysts that speed up reactions without altering the final equilibrium and they aren’t used up

Question 2

Substrate Specificity?

Answer 2

Allows enzymes to only catalyse one type of reaction which is usually determined by the active

Question 3

Oxidoreductases?

Answer 3

Add O2 or remove H2 (Lactate Dehydrogenase)

Question 4

Transferases?

Answer 4

Transfer of functional group within the same molecule (Amino transferase)

Question 5

Hydrolases?

Answer 5

Cleaves bond by addition of water (Trypsin)

Question 6

Lyases?

Answer 6

Breaks the bond between a carbon atom and another atom

Question 7

Isomerases?

Answer 7

Isomerisation reactions (Isomerase)

Question 8

Ligases?

Answer 8

Uses ATP to catalyse the formation of new covalent bonds (DNA ligase)

Question 9

What stabilises proteins?

Answer 9

H-bonds, electrostatic salt links and hydrophobic actions

Question 10

Induced fit model?

Answer 10

a change in shape of he enzyme when substrate binds to active site

Question 11

Michaelis Menton Equation?

Answer 11

Km = K2 + K-1 / K1
K1 = Enzyme substrate forming
K-1/K2 = Getting rid of ES

Question 12

Determining Initial Velocity?

Answer 12

When [S] &laquo_space;Km, rate depends linearly on [S], so [S] is rate limiting
When [S]&raquo_space; Km, rate is independant of [S], [E] is rate limiting
Rate (v) is kinetically dependant on [E] total at any given value of [S]

Question 13

Limiting velocity?

Answer 13

Vmax = K2 [E]total is the limiting velocity of the reaction at any given concentration
Obtained at saturating levels of substrate
Referred to as the maximum velocity

Question 14

Michaelis Constant?

Answer 14

When [S] = Km, V = 1/2 Vmax, so Km is the substrate concentration at half the limiting velocity
Km is a measure of the lifetime of the ES complex and indicates concentration required for significant catalysis to take place
Kcat = Vmax/[E]total and Ka = Kcat/Km

Question 15

Types of Inhibitors?

Answer 15

Reversible inhibitors - bind to enzyme and can dissociate

Irreversible inhibitors - bind permanently

Question 16

Competitive, non-competitive and incompetitive inhibitors?

Answer 16

Competitive bind directly to active site
Non-Competitive bind away from site altering enzyme shape
Incompetitive - Only binds to E-S complexes to stop product from forming

Question 17

Inhibitors effect on Km and Vmax?

Answer 17

Competitive inhibitors increase Km and dont effect Vmax. it can be overcome by increasing [S] as when [S]&raquo_space; Km, the rate is independent of Km
Non-Competitive reduces Vmax but Km is not affected. Inhibition is independent of [S] as rate always depends on Vmax

Question 18

What is allosteric regulation?

Answer 18

Where a molecule binds to an enzyme someplace other than the active site (allosteric site)

Question 19

Allosteric Enzymes?

Answer 19

They have multiple active sites and when an inhibitor binds, all active sites are changed slightly so they dont work as well. Allosteric activators can cause an increase in function.

Question 20

What are Modulators?

Answer 20

They change enzyme structure making the enzyme either less or more active (T or R state)

Question 21

What is feedback inhibiton?

Answer 21

A sequence of enzymes produce a product which inhibits initial enzymes used to start the reaction