Enzymes - Incomplete

Front 1

What is an enzyme?

Back 1

A protein catalyst that increases the rate of reactions w/o being changed in the overall process

Front 2

What is a synthetase?

Back 2

Requires ATP to function

Front 3

What is a synthase?

Back 3

no ATP required to function

Front 4

What is a phosphatase?

Back 4

Uses water to remove a phosphoryl group

Front 5

What is a phosphorylase?

Back 5

Uses Pi to break a bond and generate a phosphorylated product

Front 6

What is a dehydrogenase?

Back 6

NAD/FAD is electron acceptor in redox reactions

Front 7

What is a oxidase?

Back 7

O2 acceptor but oxygen atoms are not incorporated into substrate

Front 8

What is a oxygenase?

Back 8

One or both oxygen atoms are incorporated

Front 9

What are RNAs w/ catalytic activity?

Back 9

Ribozymes

Front 10

What does the active site contain?

Back 10

Amino acid side chains that participate in substrate binding and catalysis

Front 11

What is the induced fit model?

Back 11

The enzyme undergoes a conformational change that allows catalysis of the enzyme

Front 12

What is the holoenzyme?

Back 12

The active enzyme w/ its nonprotein component

Front 13

What is a apoenzyme?

Back 13

The enzyme w/o its nonprotein moiety, the inactive form

Front 14

What is a cofactor?

Back 14

If the nonprotein moiety of an enzyme is a metal ion such as Fe3+ or Zn2+

Front 15

What is a coenzyme?

Back 15

IF the nonprotein moiety of an enzyme is small organic molecule

Front 16

What are cosubstrates?

Back 16

Coenzymes that only transiently associate w/ the enzyme

Front 17

What are coenzymes frequently derived from?

Back 17

Vitamins

Front 18

What is the purpose of enzyme compartmentalization?

Back 18

Serves to isolate the reaction substrate or product from other competing reactions

Also provides a favorable environment for the reaction, and organizes the thousands of enzymes present in the cell into purposeful pathways

Front 19

What is the free energy of activation?

Back 19

The energy difference b/e that of the reactants and a high-energy intermediate that occurs during the formation of product

Front 20

What do molecules need in order to react?

Back 20

Enough energy to overcome the energy barrier of the transition state

Front 21

What is accomplished by the enzyme stabilizing the transition state?

Back 21

Greatly increases the concentration of the reactive intermediate that can be converted to product and accelerates the reaction

Front 22

What is the enzymes maximal velocity?

Back 22

The rate of a reaction is the number of substrate molecules converted to product per unit time

Front 23

What enzymes do not follow michaelis-menten kinetics?

Back 23

Allosteric enzymes

Front 24

What effect on reaction velocity does temperature have?

Back 24

Increased temperature increases the rate of the reaction by adding more energy

Front 25

What happens to reaction velocity if you heat it too hot?

Back 25

The enzymes denature and reaction velocity decreases

Front 26

What is the michaelis-menton equation?

Back 26

v0 = (Vmax[S])/(Km + [S])

v0 = initial reaction velocity
vmax = maximum reaction velocity
[S] = substrate concentration
Km = constant

Front 27

What assumptions are made by the michaelis-menton equation?

Back 27

1. [S] >>> [E]
2. [ES] does not change w/ time
3. The rate of the reaction is measured as soon as enzyme and substrate are mixed

Front 28

What is Km equal to?

Back 28

Numerically equal to the substrate concentration at which the reaction velocity is equal to 1/2Vmax

Front 29

What does Km reflect about the enzyme? what does a low Km mean? high Km?

Back 29

The affinity of the enzyme for that substrate

low Km = high affinity of enzyme for substrate
high Km = a low affinity of enzyme for substrate

Front 30

What is the relationship of velocity to enzyme concentration?

Back 30

The rate of the reaction is directly proportional to the enzyme concentration at all substrate concentrations

*i.e. when [E] is halved, v0 is halved too

Front 31

What is the order of a reaction?

Back 31

first order: When [S] is much less than Km, the velocity of the reaction is approximately proportional to the substrate concentration

zero order: When [S] is much greater than Km, the velocity is constant and equal to Vmax, and rate is independent of [S]

Front 32

What is competitive inhibition?

Back 32

When the inhibitor binds reversibly to the same site that the substrate would normally occupy

Front 33

What is competitive inhibition's effect on Vmax? Km? lineweaver-burk plot?

Back 33

Vmax = effect of competitive inhibitor is reversed by increasing [S], so reactions eventually reach the Vmax
Km = increases the apparent Km, so more substrate is required to reach 1/2Km
L-B = shows a characteristic plot where the inhibited and uninhibited plots intersect on the y-axis at 1/Vmax

Front 34

What is noncompetitive inhibition? what is its effect on Vmax? Km? L-B?

Back 34

When inhibition occurs at a site other than the active site

Vmax = decrease the apparent Vmax of a reaction
Km = does not interfere w/ binding, so same Km
L-B = Apparent Vmax decreases

Front 35

What is the function of allosteric enzymes?

Back 35

Alter the affinity of the enzyme for its substrate, or modify the maximal catalytic activity of the enzyme or both

Front 36

What role does alanine play in the liver?

Back 36

Transfers ammonia equivalents to the liver for processing into urea

Front 37

What is the function of the ALT enzyme? What does it require to function?

Back 37

Plays a critical role in amino acid catabolism

The vitamin B6 derivative PLP ("pyridoxal-5'-phosphate")

Front 38

What cofactor do many neurotransmitters require for their synthesis?

Back 38

PLP

Front 39

Which Michaelis-Menten kinetic parameters correlate with enzyme concentration?

Back 39

v0

Front 40

Which Michaelis-Menten parameter depends on substrate concentration? why?

Back 40

Vmax;

b/c the Vmax is determined by how much substrate you can add before you reach maximum reaction speed

Front 41

Which Michaelis-Menten kinetic parameter indicates relative substrate preferences? why?

Back 41

Kcat/Km

b/c Kcat/Km is the specificity constant and represents the enzymes ability to catalyze a particular substrate, so the lower Km and the higher Kcat the better the substrate binds to the enzyme

Front 42

What are the kinetics of indicator reactions characterized by?

Back 42

low Km values and high activity

Front 43

What is the effect of pH on enzymes?

Back 43

There is a very narrow pH range where enzymes function w/o denaturing, so the pH must be strongly buffered

Front 44

What would you consider a compound that binds to an enzyme w/o being modified?

Back 44

A potential inhibitor

Front 45

Where do Competitive, noncompetitive and mixed inhibitors intersect on a lineweaver-burk plot?

Back 45

Competitive inhibitors intersect on the y-axis

noncompetitive inhibitors intersect on the x-axis

mixed inhibitors intersect somewhere in outerspace and not on a axis

Front 46

What effect do mixed inhibitors have on binding to the enzyme-substrate complex?

Back 46

Mixed inhibitors change the conformation of the active site and prevent substrate binding. SO it has the characteristics of competitive inhibition, but does not bind to the active site

Front 47

What effect will binding of a substrate to part of an allosteric effector have?

Back 47

Will change the conformation of all sites

Front 48

What is the most common enzyme that is inhibited by uncompetitive inhibition?

Back 48

bisubstrate enzymes

Front 49

What effect on apparent Km do competitive inhibitors have?

Back 49

Make the apparent Km larger