Enzymes

Question 1

Enzymes

Answer 1

incredibly important as biological catalysts

Question 2

catalysts

Answer 2

do not impact the thermodynamics of a reaction; Hrxn and equilibrium position do not change but the reaction proceeds at a much faster rate

Question 3

Key points about enzymes

Answer 3

• lower the activation energy
• increase rate of reaction
• do not alter the equilibrium constant
• are not changed or consumed in the reaction (appear in both reactants and products)
• are pH and temperature sensitive
• do not affect the overall ΔG of reaction
• are specific for a particular reaction or class of reactions

Question 4

enzyme specifity

Answer 4

enzymes will only catalyze a single reaction/class of reactions for a particular substrate

Question 5

oxidoreductase

Answer 5

catalyze redox reactions; transfer electrons between biological molecules; often has a cofactor that acts as an electron carrier

Question 6

reductant

Answer 6

electron donor

Question 7

oxidant

Answer 7

electron acceptor

Question 8

transferase

Answer 8

catalyze the movement of a functional group from one molecule to another

Question 9

kinase

Answer 9

catalyze the transfer of a phosphate group to another molecule

Question 10

hydrolase

Answer 10

catalyze the breaking of a compound into two molecules by addition of water

Question 11

lyase

Answer 11

catalyze the cleavage of one molecule into two products; do not require water and do not act as oxidoreductases

Question 12

synthase

Answer 12

synthesis of two molecules into one molecule

Question 13

isomerase

Answer 13

catalyze the rearrangement of bonds within a molecule; catalyze reactions between stereoisomers as well as constitutional isomers

Question 14

ligases

Answer 14

catalyze addition or synthesis reactions, generally between large similar molecules and often require ATP; nucleic acid synthesis/repair

Question 15

lyase

Answer 15

catalyze addition or synthesis reactions, generally between small similar molecules and often require ATP

Question 16

endergonic reaction

Answer 16

require energy input (ΔG>0)

Question 17

exergonic reaction

Answer 17

energy is given out (ΔG<0)

Question 18

activation energy

Answer 18

catalysts lower the activation energy to make it easier for the substrate to reach its transition state

Question 19

enzyme-substrate complex

Answer 19

physical interaction between substrate and enzyme

Question 20

active site

Answer 20

the location within the enzyme where the substrate is held during chemical reaction

Question 21

lock and key theory

Answer 21

proposes that the enzymes active site is already in the appropriate conformation for the substrate to bind

Question 22

induced fit model

Answer 22

the substrate induces a change in the shape of the enzyme; the enzyme returns to its original state after the interaction

Question 23

cofactors/coenzymes

Answer 23

bind to the active site of the enzyme and participate in the catalysis of a reaction

Question 24

apoenzymes v. holoenzymes

Answer 24

apoenzymes: enzyme without its cofactors
holoenzymes: enzyme with its cofactors

Question 25

prosthetic groups

Answer 25

tightly bound cofactors/coenzymes necessary for enzyme function

Question 26

cofactors

Answer 26

generally inorganic molecules or metal ions; often digested as dietary minerals

Question 27

coenzymes

Answer 27

small organic groups, the vast majority of which are vitamins or derivates of vitamins such as NAD+, FAD or coenzyme A

Question 28

water-soluble vitamins

Answer 28

B complex and vitamin C (Ascorbic acid)

Question 29

fat-soluble vitamins

Answer 29

A,D,E,K

Question 30

saturation

Answer 30

at this rate, enzyme is working at maximum velocity (Vmax)

Question 31

Michaelis-Menten

Answer 31

E+S()ES->E+P | where is k(1) and the second -> is Kcat

Question 32

Michaelis-Menten

Answer 32

v=(Vmax[S])/(Km+[S]) or v=(Kcat[E][S])/(Km+[S]) Km=substrate concentration at which half of the enzyme's active sites are full

Question 33

Kcat

Answer 33

measures the number of substrate molecules turned over per enzyme molecule per second Vmax=[E]Kcat

Question 34

catalytic efficiency

Answer 34

Kcat/Km; a large Kcat or a small Km will result in higher catalytic efficiency

Question 35

Lineweaver-Burk plots

Answer 35

-1/Km is the intercept of the line and the x-axis | 1/Vmax is the intercept of the line with the y-axis

Question 36

cooperative enzymes

Answer 36

- represented as a sigmoidal shape - have multiple subunits/active sites - attachment to one active site can lead the other sites to go from the tense (T) state to the relaxed (R) state - detachment from one active site can lead the other states to go from the relaxed (R) state to the tense (T) state

Question 37

Hill's coefficient

Answer 37

portrays if there is cooperative binding or not Hill's coefficient > 1, positive cooperative binding Hill's coefficient < 1, negative cooperative binding Hill's coefficient = 1, no cooperative binding

Question 38

temperature and enzymes

Answer 38

- enzyme-catalyzed reactions tend to double in velocity for every 10 degrees C until optimum temp reached - after this optimal temp, activity falls off sharply as they begin to denature at high temps

Question 39

pH and enzymes

Answer 39

human enzymes work best around 7.4; work less efficiently lower or higher

Question 40

feedback inhibition

Answer 40

once there is enough of a given product, the product binds to the active site of an enzyme, making them unavailable to make more product

Question 41

competitive inhibition

Answer 41

involves occupancy of the active site; can be overcome by adding more substrate; no effect to Vmax, but Km is increased

Question 42

noncompetitive inhibition

Answer 42

bind to an allosteric site instead on the active site, which induces a change in enzyme conformation; cannot be overcome by adding more substrate; bind equally well to E and ES; lowers Vmax but does not effect Km

Question 43

mixed inhibition

Answer 43

same as noncompetitive inhibitor in that in can bind to an allosteric site on both E or ES but has different affinity for each; alters Km, decreases Vmax

Question 44

uncompetitive inhibition

Answer 44

bind only to ES complex; lowers Vmax and Km

Question 45

allosteric enzymes

Answer 45

have multiple binding sites; alternate between active and inactive forms;

Question 46

allosteric sites

Answer 46

sites different from the active sites that bind either activators or inhibitors

Question 47

covalently modified enzymes

Answer 47

enzymes can be activated or deactivated by covalent modification, aka phosphorylation

Question 48

glycosylation

Answer 48

covalent attachment of sugar to an enzyme

Question 49

zymogens

Answer 49

enzymes are secreted as zymogens; regulatory domain must be removed in order for active site to be exposed