Enzymes

Question 1

How do enzymes function as biological catalysts?

Answer 1

• they speed up biological reactions by lowering activation energy required to reach transition state of RXN
• enzymes are NOT used up in RXN’s, and at end of RXN… regenerated in original form

Question 2

Describe enzyme specificity.

Answer 2

the fact that enzymes act on a specific substrate/will only catalyze a specific RXN

Question 3

what are the names of the 6 different classes of enzymes?
(LIL’ HOT)

Answer 3

Ligase
Isomerase
Lyase
Hydrolase
Oxidoreductase
Transferase

Question 4

Describe Ligase enzymes.

Answer 4

addition or synthesis reactions, generally b/t large molecules, often require ATP
(i.e. DNA ligase)

Question 5

Describe isomerase.

Answer 5

rearrangement of bonds w/in a compound

Question 6

Describe lyase enzymes.

Answer 6

cleavage of a single molecule into two products, or synthesis of small organic molecules

Question 7

Describe hydrolase enzymes.

Answer 7

breaking of a compound into two molecules, with the addition of water

Question 8

Describe oxidoreductase enzymes.

Answer 8

catalyze oxidation reduction reactions (transfer of electrons)

Question 9

Describe transferase enzymes.

Answer 9

movement of a functional group from one molecule to another

Question 10

in what ways do enzymes affect the thermodynamics vs. the kinetics of a reaction?

Answer 10

enzymes DO NOT affect the thermodynamics of a reaction, so they do not change the ΔG or ΔH

enzymes DO lower energy required to reach transition state, so they lower activation energy of RXN

enzymes DO have profound effect on kinetics of RXN by lowering activation energy, and this causes equilibrium to be reached FASTER (position of equilibrium does not change though)

Question 11

lock and key model

Answer 11

active site of enzyme and it’s substrate fit perfectly together, as is

so, tertiary and quaternary structures NOT altered

Question 12

induced fit model

Answer 12

active site of enzyme undergoes confirmational change around substrate, only when substrate is present

tertiary and quaternary structure slightly altered for enzyme to function

Question 13

what do cofactors and coenzymes do? how do they differ?

Answer 13

cofactors and coenzymes are both activators of enzymes; in both cases, regulators induce confirmational change in enzyme to promote it’s activity

cofactors -> generally inorganic molecules (i.e.minerals)

coenzymes -> generally small organic molecules

(i.e. vitamins)

Question 14

what are the effects of increasing 〚S〛on enzyme kinetics?

Answer 14

it depends

at low〚S〛, increasing 〚S〛increases rate of reaction proportionally

at high 〚S〛, increasing 〚S〛will NOT change rate of reaction, b/c vmax already reached

Question 15

what are the effects of increasing 〚E〛on enzyme kinetics?

Answer 15

increasing 〚E〛will always increase reaction rate, no matter what the initial 〚E〛was

Question 16

how are the Michaelis-Menten and Lineweaver-Burk plots similar? how are they different?

Answer 16

similar:

• they both account for values of Km and Vmax under various conditions
• they provide simple visual representations of the variables

different:

• axes of the graphs are different, and the visual representation is different

MM: V vs.〚S〛

Lineweaver: 1/V vs. 1/〚S〛(which is straight line)

Question 17

what do the x and y intercepts of Lineweaver-Burk plot represent?

Answer 17

intercept: -1/Km

y-intercept: 1/Vmax

Question 18

what is enzyme cooperativity?

Answer 18

allosteric regulation where an enzyme becomes more receptive to bonding with additional substrate molecules after one substrate molecule attaches to an active site (i.e.once hemoglobin bonds one oxygen molecule, it’s easier for the other three to binds)

Question 19

what are the effects of temperature on the function of enzymes?

Answer 19

as temp ↑, rate of RXN ↑, BUT at a certain pt. temp is too HIGH, and proteins begin to denature

Question 20

what are the effects of pH on the function of enzymes?

Answer 20

enzymes are maximally active in small pH range, and outside of range, activity drops quickly

Question 21

what are the effects of salinity on the function of enzymes?

Answer 21

changes in salinity can disrupt bonds w/in quaternary structure, which leads to loss of function of enzymes

Question 22

whats the ideal enzymes for most enzymes in the body?

Answer 22

37 C, 98.6 F, 310 K

Question 23

what is feedback inhibition?

Answer 23

when the product of a reaction (thats near end of a chain) inhibits the function of an enzyme in an earlier reaction of the chain

Question 24

competitive inhibition

Answer 24

• a substance that resembles the normal substrate competes with the substrate at the enzymes active site
• inhibition CAN be overcome by adding more substrate

Question 25

what are the four types of reversible inhibitor?

Answer 25

competitive inhibition
non-competitive inhibition
mixed inhibition
uncompetitive inhibition

Question 26

interpretation of Km

Answer 26

low Km = high affinity of substrate AND enzyme

high Km = low affinity of substrate AND enzyme

Question 27

non-competive inhibition

Answer 27

• inhibitor binds to allosteric site on enzyme, so it can bind to either the free E OR to ES
• complex decreases the catalytic ability of the enzyme
• inhibition CAN’T be overcome by adding more substrate

Question 28

Describe where a competitive inhibitors bind in an enzyme.

Answer 28

Active site of enzyme

Question 29

Describe what happens to Km and Vmax during competitive inhibition.

Answer 29

impact on Km: Km ↑( b/c more substrate needed to reach 1/2vmax)

impact on Vmax: unchanged (b/c if enough substrate is present, it can outcompete inhibitor. thus, vmax can still be achieved)

Question 30

Describe where noncompetitive inhibitors bind to in an enzyme.

Answer 30

Allosteric site

Question 31

Describe what happens to Km and Vmax during noncompetitive inhibition.

Answer 31

impact on Km = unchanged (b/c inhibitor does not bind to active site, so enzymes affinity for substrate SAME)

impact on Vmax = decreases Vmax (b/c less enzyme available to react w/ substrate, to make product. this is b/c if inhibitor binds to allosteric site, it will causes confirmational change of enzyme, and enzyme will no longer be able to make product).

Question 32

Describe how mixed inhibitors bind to enzymes.

Answer 32

inhibitor can bind to allosteric site in either enzyme OR enzyme-substrate complex BUT has different affinity for each

Question 33

Describe how mixed inhibitors affect Km.

Answer 33

if inhibitor preferentially binds to enzyme = it increases Km value (lowers affinity)

if inhibitor preferentially binds to enzyme-substrate complex = it lowers Km value (increases affinity)

Question 34

Describe uncompetitive inhibition.

Answer 34

• inhibitor binds only to enzyme-substrate complex
• when inhibitor bound, it locks substrate in enzyme preventing its release (increasing affinity of enzyme w/ substrate, so lower Km)

Question 35

Describe the impact of a uncompetitive inhibitor on Km and Vmax.

Answer 35

impact on Km: decreases (this is b/c w/ present of inhibitor, it prevents substrate from being able to be released. so, Km lower (affinity of enzyme w/ substrate increased)

impact on Vmax: decreases

Question 36

what is irreversible inhibition?

Answer 36

active site is made unavailable for a long period of time, or the enzyme is permanently altered; thus, enzymes CAN’T be easily renatured to perform it’s function

Question 37

what are examples of covalent enzyme modifications?

Answer 37

phosphorylation/de-phosphorylation

glycosylation

Question 38

why are some enzymes released as zymogens?

Answer 38

they are precursors of an active enzyme; it’s critical that certain enzymes (i.e. digestive enzymes pancreas) remain inactive until they arrive to target site