Enzymes

Question 1

oxidoreductase

Answer 1

catalyze oxidation-reduction reactions. Often use cofactors such as NAD+
–> dehydrogenase or reductase

Question 2

transferases

Answer 2

shift functional group from one molecule to another

ex: kinases

Question 3

hydrolases

Answer 3

cleaves molecule using the addition of water

Question 4

lyases

Answer 4

split molecules without water, often forms ring/cyclic structures

Question 5

isomerases

Answer 5

catalyze rearrangement of bonds within a molecule

functions with stereoisomers and constitutional isomers

Question 6

ligases

Answer 6

use ATP to join large biological molecules

Question 7

enzymes

Answer 7

catalysts that lower the activation energy of a reaction. They do not affect the equilibrium, do not change the overall free energy change (/\ G). They affect the rate (kinetics) at which the reaction occurs

Question 8

coenzymes

Answer 8

organic molecules that enzymes need

ex: vitamins, NAD+

Question 9

soluble vitamins

Answer 9

B and C

Question 10

cofactors

Answer 10

inorganic and metal cations

ex: minerals

Question 11

holoenzyme

Answer 11

everything needed is present

Question 12

apoenzyme

Answer 12

missing something, cannot function

Question 13

prosthetic groups

Answer 13

tightly bound cofactors or coenzymes that are necessary for enzyme function

Question 14

B vitamins

Answer 14

B1: thiamine
B2: riboflavin
B3: niacin
B7: biotin
B9: folic acid

Question 15

how to increase vmax

Answer 15

increasing enzyme concentration –> inducing the expression of the gene encoding the enzyme

Question 16

Michaelis-Menten equations

Answer 16

describes how the rate of the reaction, v, depends on the concentration of enzyme and substrate
E + S ES E + P

Question 17

Michaelis-Menten equation when [E] is constant

Answer 17

v = vmax [S] / Km + [S]

Question 18

Km

Answer 18

measure the affinity of the enzyme for its substrate. Intrinsic property that cannot be altered by changing concentration

Question 19

kcat

Answer 19

number of substrate molecules “turned over” per enzyme molecule per second (units s-1)
vmax = [E] Kcat

Question 20

catalytic efficient

Answer 20

kcat/ km

large turn over (large kcat) or high affinity (small Km) will result in higher efficiency

Question 21

Lineweaver-Burk plots

Answer 21

y axis: 1/v y intercept: 1/vmax

x axis: 1/[S] x intercept: 1/ Km

Question 22

cooperativity

Answer 22

binding of a substrate encourages the transition of the other subunits from the T (low affinity tense state) to R (high affinity relaxed state)
Sigmoidal graph

Question 23

Hill’s coefficient

Answer 23

in regards to cooperativity
H > 1 –> positively cooperative
H = 1 –> no cooperativity
H < 1 –>negatively cooperative (one ligand decreases affinity)

Question 24

what affect enzyme rate

Answer 24

temperature: ideal ~ 37 C
pH: in general pH 7.4, but stomach enzymes function at lower pHs
salinity: increasing levels of salt disrupt H-bonds in vitro

Question 25

competitive inhibition

Answer 25

inhibitor competes for active site. increasing [S] overcomes effect
Vmax is the same (y - intercept does not change)
Km changes ( x-intercept changes)
--> all lines cross at the same y-intercept

Question 26

noncompetitive inhibitor

Answer 26

binds to allosteric site, inducing a change in enzyme conformation
inhibitor has the same affinity for [E] and [ES] complex
decreases Vmax because there is less active enzymes
does not change Km because the affinity for the substrate of the active enzymes is the same
–> lines meet at x intercept

Question 27

mixed inhibitor

Answer 27

binds to allosteric site but has different affinities for [E] or [ES- complex]
Affects both Vmax and Kmax

Question 28

uncompetitive inhibitor

Answer 28

binds only to [ES-complex], locking the substrate in the enzyme, preventing its release
lowers Km and Vmax

Question 29

allosteric enzymes

Answer 29

have multiple binding sites. can be in active or inactive form depending if it is bound to allosteric activators or inhibitor. often have sigmoidal curve

Question 30

covalently bound enzymes

Answer 30

often activated/deactivated by phosphorylation

glycosylation can also cause covalent changes

Question 31

zymogens

Answer 31

inactive forms of enzymes . regulatory domain must be removed or altered to activate enzyme
ex: trypsin, released by the pancreas as trypsinogen and activated in stomach