enzymes 1

Question 1

are enzymes chemically altered in a reaction?

Answer 1

no

Question 2

how do enzymes increase the rate of a reaction?

Answer 2

by providing an alternative reaction pathway with a lower activation energy

Question 3

what conditions do enzymes work under?

Answer 3

physiological conditions (moderate temperature, around neutral pH, low concentrations of substrate, aqueous environment)

Question 4

what is the active site?

Answer 4

enzymes work by forming complexes with their substrate by binding to them at the active site, providing a unique microenvironment for the reaction to proceed. Very high specificity for reaction catalysed AND substrate used.

Question 5

as the substrate concentration is increased what happens to the velocity of the reaction?

Answer 5

the velocity increases

Question 6

what is increased steadily until a maximum rate of reaction is reached?

Answer 6

the rate of a reaction increases as the substrate concentration increases until Vmax is reached

Question 7

what type of graph can be plotted to calculate the Vmax?

Answer 7

a Lineweaver-Burke Plot

Question 8

what is the first michaelis-menten equation?

Answer 8

K-1 + K2/K+1 = Km
where K+1 is the rate of formation of the complex, K-1 is the rate at which the complex changes back into substrates and K2 is the rate of formation of end products

Question 9

what is the second michaelis-menten equation?

Answer 9

Vo = Vmax [S]/Km + [S]

where Vo is the initial reaction velocity, [S] is the substrate concentration and Vmax is the maximum reaction velocity

Question 10

what is Km?

Answer 10

Michaelis constant; it is the substrate concentration required for half maximum velocity

Question 11

what are irreversible enzyme inhibitors?

Answer 11

substances that react with the enzyme to form a covalent adduct with the protein.

Question 12

what does diisopropyl fluorophosphate (DIPF) do?

Answer 12

this is an organophosphate pesticide which inhibits the enzyme acetylcholinesterase (AChE) which breaks down the neurotransmitter acetylcholine into choline and acetic acid.

Question 13

how does DIPF inactivate AChE?

Answer 13

by phosphorylating the serine hydroxyl group located at the active site of the enzyme. This results in an accumulation of ACh throughout the nervous system, resulting in overstimulation of receptors.

Question 14

what are the functions of aspirin? (acetylsalicylic acid)

Answer 14

it is an antipyretic, anti-inflammatory and analgesic

Question 15

what enzyme does aspirin inhibit?

Answer 15

cyclooxyrgenase-1 (COX-1) which catalyses the conversion of arachidonic acid (AA) to prostaglandin H2 (PGH2) which is a precursor for synthesis of inflammatory mediators

Question 16

how does aspirin inhibit COX-1?

Answer 16

by reacting with a serine residue close to the active site which prevents the substrate from binding.

Question 17

what is a competitive inhibitor?

Answer 17

a competitive inhibitor is a drug that can compete with the substrate for the active site of the enzyme. Similar structure to the substrate and leaves the active site unchanged.

Question 18

how is the action of an enzyme affected by a competitive inhibitor?

Answer 18

the action of the enzyme is slowed down.

Question 19

what is the name of the chemicals that competitively inhibit the enzyme bacteria use to synthesise folic acid?

Answer 19

sulphonamides which are similar in structure to the substrate, 4-aminobenzoic acid

Question 20

what is needed to reach the Vmax for a competitively inhibited reaction?

Answer 20

a higher substrate concentration, Vmax is unchanged. Results in an increase in Km

Question 21

what type of graph can competitive inhibition be shown on ?

Answer 21

a line weaver-burke plot. The enzymes with a higher concentration of inhibitor have a steeper gradient.

Question 22

what are allosteric inhibitors?

Answer 22

inhibitors that bind to the enzyme away from the active site and changes the conformation of the enzyme, meaning that the substrate cannot bind to the enzyme anymore

Question 23

what happens to Vmax inn allosteric inhibition?

Answer 23

VMax decreases

Question 24

what often (but not always) happens to Km with allosteric inhibition?

Answer 24

Km increases

Question 25

what reaction does phosphofructokinase catalyse?

Answer 25

the transfer of phosphate from ATP to fructose 6-phosphate, which is an important step in glycolysis

Question 26

how does ATP prevent glycolysis from proceeding?

Answer 26

by binding at both the active site and the inhibitory site, preventing fructose 6-phosphate from binding. Therefore glycolysis does not take place as it appears that no ATP is needed.

Question 27

what competes with ethylene glycol for the alcohol dehydrogenase active site?

Answer 27

ethanol

Question 28

what type of enzymes are involved in oxidation/reduction reactions?

Answer 28

oxidoreductases (eg alcohol dehydrogenase)

Question 29

what type of enzymes are involved in the transfer of functional groups?

Answer 29

transferases (eg hexokinase)

Question 30

what type of enzymes are involved in hydrolysis reactions?

Answer 30

hydrolases (eg trypsin)

Question 31

what type of enzymes are involved in the addition of double bonds?

Answer 31

lyases (eg carbonic anhydrase)

Question 32

what type of enzymes are involved in isomerisation reactions?

Answer 32

isomerases (eg L-alanine isomerase)

Question 33

what type of enzymes are involved in the formation of bonds with ATP cleavage?

Answer 33

ligases (eg glutamine synthase)