Enzymes

Question 1

What is enzyme specificity?

Answer 1

A given enzyme will only catalyze a single reaction or class of reactions with these substrates

Question 2

Oxidoreductases

Answer 2

Enzymes that catalyze oxidation-reduction reactions - transfer of electrons between biological molecules

Question 3

What cofactor do many oxidoreductases have?

Answer 3

One that acts as an electron carrier - NAD+ or NADP+

Question 4

Reductant

Answer 4

Electron donor

Question 5

Oxidant

Answer 5

Electron acceptor

Question 6

What class of enzymes does a dehydrogenase fall within?

Answer 6

Oxidoreductase

Question 7

What class of enzymes does a reductase fall within?

Answer 7

Oxidoreductase

Question 8

Transferases

Answer 8

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

Question 9

What class of enzymes does a kinase fall within?

Answer 9

Transferase

Question 10

What do kinases do?

Answer 10

Catalyze the transfer of a phosphate group (usually from ATP) to another molecule

Question 11

Hydrolases

Answer 11

Enzymes that catalyze the breaking of a compound into two molecules using the addition of water

Question 12

What class of enzymes does a nuclease fall within?

Answer 12

Hydrolase

Question 13

What class of enzymes does a phosphatase fall within?

Answer 13

Hydrolase

Question 14

Lysases

Answer 14

Enzymes that catalyze the cleavage of a single molecule into two products WITHOUT the use of water as a substrate

Question 15

What is a lysase often called when catalyzing its reverse reaction?

Answer 15

Synthase

Question 16

Isomerase

Answer 16

Enzyme that catalyzes the rearrangement of bonds within a molecule

Question 17

Ligases

Answer 17

Enzyme that catalyzes addition or synthesis reactions, generally between large, similar molecules, often requiring ATP

Question 18

What class of enzymes would catalyze the synthesis of small molecules?

Answer 18

Lysase

Question 19

What class of enzymes would catalyze the synthesis of large molecules?

Answer 19

Ligase

Question 20

What type of molecules are cofactors typically?

Answer 20

Inorganic or metal ions

Question 21

How does the body obtain cofactors?

Answer 21

Diet

Question 22

What type of molecules are coenzymes typically?

Answer 22

Small organic groups

Question 23

How does the body obtain coenzymes?

Answer 23

Vitamins

Question 24

Prosthetic groups

Answer 24

Cofactors or coenzymes that are tightly bound to an enzyme and are necessary for enzyme function

Question 25

Apoenzymes

Answer 25

Enzyme without its cofactor

Question 26

Holoenzymes

Answer 26

Enzyme with its cofactor

Question 27

Enzyme saturation

Answer 27

No active sites are left and reaction cannot go any faster

Question 28

How can Vmax be increased?

Answer 28

Adding more enzyme

Question 29

Describe Michaelis-Menten Plot

Answer 29

x axis has substrate concentration y axis has reaction velocity Km is the substrate concentration at half of Vmax Slope increases and then reaches Vmax

Question 30

Michaelis-Menten Equation

Answer 30

v=(Vmax[S])/(Km+[S])

Question 31

When comparing two enzymes, does a higher Km suggest a higher or lower enzyme affinity?

Answer 31

Lower - requires more substrate to reach half-saturated

Question 32

Describe Lineweaver-Burk Polot

Answer 32

``` Double reciprocal of Michaelis-Menten Plot x axis is 1/[S] y axis is 1/v x-intercept is 1/Km y-intercept is 1/Vmax ```

Question 33

How does enzyme cooperativity affect the Michaelis-Menten Plot?

Answer 33

Becomes sigmoidal - Substrate binding encourages change in shape from tense to relax, further improving enzyme affinity for substrate

Question 34

Hill's coefficient

Answer 34

Numerical quantification of cooperativity

Question 35

Hill coefficient >1

Answer 35

Positive cooperation - binding of substrate improves enzyme affinity for more substrate

Question 36

Hill coefficient <1

Answer 36

Negative cooperation - binding of substrate decreases enzyme affinity for more substrate

Question 37

Hill coefficient =1

Answer 37

Enzyme does not exhibit cooperative binding

Question 38

What are the four types of reversible enzyme inhibition?

Answer 38

Competitive Non-competitive Mixed Uncompetitive

Question 39

What occurs to the enzyme in competitive inhibition?

Answer 39

Inhibitor binds to the active site

Question 40

How is competitive inhibition overcome?

Answer 40

Add more substrate

Question 41

Does competitive inhibition change Vmax and why?

Answer 41

No - if enough substrate is added it will still run at maximum velocity

Question 42

Does competitive inhibition change Km and why?

Answer 42

Yes - more substrate will be needed to reach half of Vmax

Question 43

What occurs to the enzyme in noncompetitive inhibition?

Answer 43

Inhibitor binds to an allosteric site and induces a change in enzyme conformation (can bind either enzyme or enzyme-substrate complex with same affinity)

Question 44

Does noncompetitive inhibition change Vmax and why?

Answer 44

Yes - lowers it because there is less enzyme available to react

Question 45

Does noncompetitive inhibition change Km and why?

Answer 45

No - the noncompetitive inhibitor does not change the affinity for substrate and adding more will not change the reaction

Question 46

Allosteric site of an enzyme

Answer 46

Non-catalytic site that binds regulators

Question 47

What occurs to the enzyme in mixed inhibition?

Answer 47

Inhibitor can bind either the enzyme or enzyme-substrate complex with different affinities

Question 48

Does mixed inhibition change Vmax and why?

Answer 48

Yes - lowers it because there is less enzyme available to react

Question 49

Does mixed inhibition change Km and why?

Answer 49

Yes - it raises Km if it preferentially binds to the enzyme and it lowers Km if it preferentially binds to the enzyme-substrate complex

Question 50

What is similar and different about noncompetitive and mixed inhibitors?

Answer 50

Both can bind to both the enzyme alone and the enzyme-substrate complex. Noncompetitive have the same affinity for both while mixed have different affinities

Question 51

What occurs to the enzyme in uncompetitive inhibition?

Answer 51

Inhibitor binds to allosteric site only to enzyme-substrate complex and locks the substrate into the enzyme

Question 52

Does uncompetitive inhibition change Vmax and why?

Answer 52

Yes - lowers it because reaction cannot reach full speed

Question 53

Does uncompetitive inhibition change Km and why?

Answer 53

Yes - lowers it because technically increases enzyme affinity by keeping substrate locked into enzyme

Question 54

When is irreversible inhibition most applicable?

Answer 54

Drugs / medications - irreversibly bind to enzymes that modulate pain or inflammatory pathways, for example

Question 55

Allosteric enzymes

Answer 55

Have multiple binding sites and alternate between an active and inactive form

Question 56

What are examples of covalent enzyme modifications?

Answer 56

Phosphorylation, glycosylation

Question 57

Zymogens

Answer 57

Inactive forms of very dangerous enzymes such as apoptotic or strong digestive enzymes that contain an active and regulatory domain - the regulatory domain must be altered to expose the active site