Chapter 2: Enzymes

Question 1

________________ catalyze redox reactions; that is, the transfer of electrons between biological molecules.

Answer 1

Oxidoreductases

Question 2

Oxidoreductases often have a ____________ that acts as an electron carrier.

Answer 2

cofactor

Question 3

In reactions catalyzed by oxidoreductases, the electron donor is known as the ____________, and the electron acceptor is known as the ____________.

Answer 3

reductant; oxidant

Question 4

Enzymes with ________________ or ____________ in their names are usually oxidoreductases. Enzymes in which oxygen is the final electron acceptor often in include ____________ in their names.

Answer 4

dehydrogenase, reductase, oxidase

Question 5

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

Answer 5

transferase

Question 6

____________ are a type of transferase that catalyze the transfer of a phosphate group, generally from ATP, to another molecule.

Answer 6

kinase

Question 7

____________ catalyze the breaking of a compound into 2 molecules using the addition of water. They are usually named for their substrate.

Answer 7

hydrolase

e.g. phosphatase cleaves phosphate group from another molecule

Question 8

________ catalyze the cleavage of a single molecule into 2 products.

Answer 8

lyases

Question 9

Lyases differ from hydrolases because of what?

Answer 9

They do not require water as a substrate

Question 10

Because most enzymes can also catalyze the reverse of their specific reactions, the synthesis of 2 molecules into a single molecule may also be catalyzed by a lyase. In this case, they are commonly referred to as ____________.

Answer 10

synthases

Question 11

____________ catalyze the rearrangement of bonds within a molecule. Can catalyze reactions between stereoisomers as well as constitutional isomers.

Answer 11

isomerases

Question 12

____________ catalyze addition or synthesis reactions, generally between large similar molecules and often require ATP.

Answer 12

ligases

Question 13

How do ligases differ from lyases?

Answer 13

ligases are for larger molecules, and lyases are for smaller molecules

Question 14

What are the major enzyme classifications?

LIL’ HOT.

Answer 14

1. Ligase
2. Isomerase
3. Lyase
4. Hydrolase
5. Oxidoreductase
6. Transferase

Question 15

An ____________ rxn is one that requires energy input. What is its ΔG?

Answer 15

endergonic; >0

Question 16

An ____________ rxn is one in which energy is given off. What is its ΔG?

Answer 16

exergonic; <0

Question 17

Enzymes do NOT alter the overall ________ ____________ change for a reaction, nor do they change the ____________.

Answer 17

free energy; equilibrium

Question 18

What do enzymes affect about reactions?

Answer 18

The rate/kinetics

Question 19

Catalysts exert their effect by lowering the ________________ ________ of a reaction. They make it easier for the substrate to reach the transition state.

Answer 19

activation energy

Question 20

The ________ ________ is the location within the enzyme where the substrate is held during the chemical reaction.

Answer 20

active site

Question 21

The ________ and ____ theory suggests that the enzyme’s active site (lock) is already in the appropriate conformation for the substrate to bind.

Answer 21

lock and key

Question 22

The ____________ ________ model, the substrate has induced a change in the shape of the enzyme. This interaction requires energy (endergonic). Once the substrate releases the enzyme, the enzyme reverts back, which releases energy (exergonic).

Answer 22

induced fit

Question 23

Many enzymes require nonprotein molecules called ____________ or ____________ to be effective. They tend to be small in size so they can bind to the active site of the enzyme and participate in catalysis.

Answer 23

cofactors or coenzymes

Question 24

Enzymes without their cofactors are called ____________, whereas those containing them are ________________.

Answer 24

apoenzymes; holoenzymes

Question 25

Tightly bound cofactors or coenzymes that are necessary for enzyme function are known as ________________ ________.

Answer 25

prosthetic groups

Question 26

Cofactors are generally what type of molecules? In what form are they ingested?

Answer 26

inorganic molecules or metal ions; ingested as dietary minerals

Question 27

____________ are small organic groups, mostly vitamins or derivatives of vitamins, e.g. NAD+, FAD, and coenzyme A.

Answer 27

Coenzymes

Question 28

The fat-soluble vitamins, A, D, E, and K, are better regulated by ________________ ____________, which quanitify the ability of a molecule to dissolve in a polar vs. nonpolar environment.

Answer 28

partition coefficient

Question 29

What affects how fast a reaction will occur?

Answer 29

The concentrations of substrate and enzyme

Question 30

A reaction cannot go any faster once it has reached ____________.

Answer 30

saturation

Question 31

When saturation is reached, the enzyme is working at maximum ____________. How is this denoted?

Answer 31

velocity; v_max

Question 32

How can you increase v_max?

Answer 32

Increase the enzyme concentration

Question 33

What does the Michaelis-Menten equation describe?

Answer 33

How the rate of the reaction, v, depends on the concentration of both the enzyme [E], and the substrate [S], which forms product [P]

Question 34

Enzyme-substrate complexes form at a rate _____.

Answer 34

k_1.

Question 35

The ES complex can either dissociate at a rate ____ or turn into E + P at a rate ____.

Answer 35

k_{-1 or kcat}

Question 36

K_{m is what?}

Answer 36

the Michaelis constant - the substrate concentration at which half of the enzyme’s active sites are full

Question 37

What does K_{m a measure of?}

Answer 37

The affinity of the enzyme for its substrates

Question 38

How can we compare enzymes using K_m?

Answer 38

The one with the higher K_{m has the lower affinity for its substrate because it requires a higher substrate concentration to be half-saturated}

Question 39

When [S] is less than K_{m, what effects reaction rate the most?}

Answer 39

changes in substrate concentration

Question 40

When [S] exceeds K_{m, the reaction rate increases much more _________ as it approaches vmax, where it becomes independent of [S].}

Answer 40

slowly

Question 41

How do we measure maximum enzyme velocity?

Answer 41

moles of enzyme per second

Question 42

What does k_{cat measure?}

Answer 42

The number of substrate molecules converted to product per enzyme molecule per second

Question 43

What is catalytic efficiency?

Answer 43

ratio of k_cat/Km

the higher, the more efficient

Question 44

________________ enzymes have multiple subunits and multiple active sites.

Answer 44

Cooperative

Question 45

What shape is the Michaelis-Menten plot of cooperative enzymes?

Answer 45

sigmoidal

Question 46

What 2 states do subunits and enzymes exist in?

Answer 46

low-affinity tense state (T) or high-affinity relaxed state (R)

Question 47

Binding of the substrate encourages subunits to transition from what state to the other?

Answer 47

T state to R state

low to high affinity

Question 48

Cooperativity is quantified by ________ ________________.

Answer 48

Hill’s coefficient

Question 49

What do different values of Hill’s coefficient mean?

Answer 49

> 1, positive cooperativity
<1 negative cooperativity
=1 no cooperativity

Question 50

Enzyme-catalyzed reactions tend to double in velocity every ____degree C increase in temperature until optimum temperature is reached. What is optimal temp?

Answer 50

10; 37

Question 51

Most enzymes also depend on pH in order to function properly. What is optimal?

Answer 51

7.4

Question 52

What are the 4 types of reversible inhibition?

Answer 52

1. competitive*
2. noncompetitive*
3. mixed
4. uncompetitive

*most common

Question 53

________________ inhibition simply involves occupancy of the active site by an inhibitor

Answer 53

Competitive

Question 54

How can competitive inhibition be overcome?

Answer 54

Add more substrate so that the substrate-to-inhibition ratio is higher

Question 55

What does a competitive inhibitor not alter?

Answer 55

It doesn’t alter vmax, because if enough substrate is added, it will reach vmax anyway.

Question 56

Really know this!

What does a competitive inhibitor alter?

Answer 56

It alters K_{m, because [S] has to be higher to reach half the maximum velocity in the presence of the inhibitor}

Question 57

________________ inhibitors bind to an allosteric site instead of the active site, which induces a change in conformation.

Answer 57

noncompetitive

Question 58

____________ sites are non-catalytic regions of the enzyme that bind regulators.

Answer 58

allosteric

Question 59

Noncompetitive inhibition cannot be overcome just by ____________, unlike competitive inhibition.

Answer 59

adding more substrate

Question 60

Noncompetitive inhibitiors bind equally well to what 2 things?

Answer 60

1. Enzyme
2. Enzyme-substrate complex

Question 61

Adding a noncompetitive inhibitor ____________ the measured value of v_{max because there is less enzyme available to react.}

Answer 61

decreases

Question 62

Know this well!

Adding a noncompetitive inhibitor does NOT alter the value of ____ because any copies of the enzyme that are still active maintain the same affinity for their substrate.

Answer 62

K_m

Question 63

________ inhibition results when an inhibitor can bind to either the enzyme or the enzyme-substrate complex, but has different affinity for each.

Answer 63

Mixed

Question 64

If an inhibitor has the same affinity for both the enzyme and enzyme-substrate complex, it is a ____________________ inhibitor.

Answer 64

noncompetitive

Question 65

Mixed inhibition alters the experimental value of ____ depending on the preference of the inhibitor for the enzyme vs. the ES complex.

Answer 65

K_m

Question 66

Mixed inhibition

If an inhibitor preferentially binds to the enzyme, it ____________ the K_{m value. This ____________ affinity.}

Answer 66

increases, lowers

Question 67

Mixed inhibition

If the inhibitor binds to the enzyme-substrate complex, it ________ the K_{m value, which ____________ affinity.}

Answer 67

lowers; increases

Question 68

mixed inhibition

Regardless if the inhibitor binds to the enzyme or enzyme-substrate complex, it ________________ v_max.

Answer 68

decreases

Question 69

For mixed inhibition, the curves on a Lineweaver-Burk plot will intersect at a point that is where?

Answer 69

not on either axis

Question 70

________________ inhibitors bind only to the ES complex and essentially lock the substrate in the enzyme, preventing its release.

Answer 70

Uncompetitive

Question 71

Why do uncompetitive inhibitors lock substrate in the enzyme and prevent its release?

Answer 71

The affinity between enzyme and substrate is increased

Question 72

Because the enzyme-substrate complex has already formed upon binding, uncompetitive inhibitors must bind at an ________________ site.

Answer 72

allosteric

Question 73

What allows an uncompetitive inhibitor to bind to an allosteric site?

Answer 73

The formation of the ES complex that creates a conformational change

Question 74

What effect do uncompetitive inhibitors have on Km and vmax?

Answer 74

lowers them!

Question 75

On a Lineweaver-Burk plot, the curves for activity with and without an uncompetitive inhibitor are ____________.

Answer 75

parallel

Question 76

In ____________ inhibition, the active site is made unavailable for a prolonged period of time, or the enzyme is permenantly altered. Not easily reversed or overcome.

Answer 76

Irreversible

prime drug mechanism

Question 77

Enzymes that are ____________ have multiple binding sites. These other sites can regulate the activity of the active site.

Answer 77

allosteric

Question 78

Allosteric enzymes alternate between an active and an inactive form. Molecules that bind to the allosteric site can be ?

Answer 78

Allosteric activators or inhibitors

Question 79

Enzymes are often subject to covalent modification, such as ____________________ or ________________.

Answer 79

phosphorylation, glycosylation

Question 80

____________ is the covalent attachment of sugar moieties.

Answer 80

Glycosylation

Question 81

Certain enzymes can be dangerous if not tightly controlled. They may even digest the organ from which it is released, e.g. pancreas and trypsin. To avoid this danger, many enzymes are secreted as inactive ________________ like trypsinogen.

Answer 81

zymogens

Question 82

What do zymogens contain? How do they work?

Answer 82

Zymogens contain a catalytic (active) domain and regulatory domain. The regulatory domain must be either removed or altered to expose the active site.

Question 83

Apoptotic enzymes, ____________, exhibit similar regulation to zymogens.

Answer 83

caspases

Question 84

What suffix do most zymogens have?

Answer 84

-ogen