enzymes 1

Question 1

enzyme definition

Answer 1

globular proteins that lower activation energy and speeding up rate of chemical reactions by stabilising transition states

Question 2

enzymes can be referred to biological catalysts. how do they differ from chemical catalysts?

Answer 2

• Catalyse very high reaction rates
• Shows great reaction specificity
  – Work in mild temperature/pH conditions
  – Can be regulated

Question 3

define co factor

Answer 3

non-protein compound or ion
aid catalysis by transferring functional groups or electrons
either organic (derived from vitamins) or inorganic (metal ions)

Question 4

define co enzyme

Answer 4

type of co-factor
organic molecule

Question 5

define prosthetic group

Answer 5

cofactor that is covalently bound or very tightly associated with he enzyme

Question 6

define apoenzyme

Answer 6

protein component of an enzyme containing a cofactor

Question 7

define holoenzyme

Answer 7

“whole enzyme”
apoenzyme + cofactor(s)

Question 8

define substrate

Answer 8

molecule acted on by the enzyme

Question 9

define active site

Answer 9

part of the enzyme in which the substrate binds and is acted upon

Question 10

reaction type of oxidoreductases (1)

Answer 10

transfer electrons

Question 11

reaction type of transferases (2)

Answer 11

group transfers

Question 12

reaction types of hydrolyases (3)

Answer 12

hydrolysis (transfer chemical groups to water)

Question 13

reaction type of lyases (4)

Answer 13

form, or add group to double bonds

Question 14

reaction type of isomerases (5)

Answer 14

transfer group within molecules (form isomers)

Question 15

reaction type of ligases (6)

Answer 15

formation of C-C, C-S, C-O and C-N bonds (coupled to ATP cleavage)

Question 16

function of enzymes:

Answer 16

• increase the rate of spontaneous reactions
• lower activation energy of biochemical reactions
• accelerate movement towards react equilibrium

Question 17

how do enzymes reduce activation energy?

Answer 17

• entropy reduction
• desolvation
• induced fit

Question 18

entropy reduction

Answer 18

Molecules in free solution will only react by “bumping” into one another
Enzymes “force” the substrate(s) to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed

Question 19

desovlation

Answer 19

• weak bonds between the substrate and enzyme replace most or all of the H-bonds between substrate and aqueous solution

Question 20

induced fit

Answer 20

• conformation changes occur in protein stature as substrate binds

Question 21

techniques used to understand enzyme function

Answer 21

• enzyme kinetics
• mutagenesis
• 3D structure

Question 22

energy barrier definition

Answer 22

the minimal amount of energy that is necessary to launch a chemical reaction

Question 23

explain concentrations of hexokinase and glucokinase post meal

Answer 23

• post meal = high [blood glucose]
• glucokinase activity inc as repsonse in inc bg
• hexokinase already at Vmax and so stays at constant rate
• allows glucokinase to respond proportionally to [bg]

Question 24

explain concentrations of hexokinase and glucokinase at low [blood glucose]

Answer 24

• gluconeogenesis releases glucose from liver
• glucokinase cannot catalyse glucose to G6P when [gb] low
• this prevents glucose phosphorylation allowing glucose to be available for immediate use and not trapped in liver

Question 25

isoenzyme definition

Answer 25

different proteins but catalyse same reaction

Question 26

In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the:

Answer 26

intercept on the
1/[S] axis

Km increases because the inhibitor competes with the substrate to bind to the enzyme’s active site

so intercept on the axis shifts right, indicating an increase in Km
​
.

Question 27

increase in km means:

Answer 27

High values of KM = low enzyme affinity for substrate (it takes more substrate to get to Vmax )
Low KM values = high affinity for substrate.

Question 28

heterotrophic modulator of allosteric protein

Answer 28

external molecule or ligand that binds to a regulatory site on the protein, inducing a conformational change that alters the protein’s activity.

Question 29

homographic modulator of allosteric protein

Answer 29

a molecule that acts as both a substrate for the enzyme’s catalytic reaction and as a regulatory molecule that affects the enzyme’s activity through binding to its allosteric site(s).

Question 30

Which statement is correct about the Michaelis-Menten parameters Vmax and KM? a. KM = Vmax when V0 = 1/2 Vmax b. Vmax is attained when [S] &laquo_space;KM c. Vmax does not depend on the total enzyme concentration in the reaction. d. A compound that exhibits mixed inhibition will both decrease Vmax and increase KM.

Answer 30

d