Thermodynamics, Reaction Coupling, and Enzymes

Question 1

what is gibbs free energy equation

Answer 1

deltaG = deltaH - (deltaT)(deltaS)

Question 2

What deltaG values make a rxn spontaneous and nonspontaneous?

Answer 2

Spontaneous/exergonic = deltaG <0

Nonspontaneous/endergonic = deltaG >0

Question 3

what is deltaH?

Answer 3

enthalpy-it’s the potential energy

Question 4

what is deltaS?

Answer 4

entropy-it’s the kinetic energy

Question 5

distinguish between exergonic and endergonic

Answer 5

endergonic = release of heat

exergonic = release of any type of energy

all endergonic rxns are exergonic, but not all exergonic rxns are endergonic

Question 6

what is reaction coupling?

Answer 6

refers to coupling an endergonic rxn to an exergonic rxn to make a rxn proceed in the forward direction and thus making the overall rxn spontaneous

Question 7

____ hydrolysis is coupled with other rxns to drive other endergonic rxns within the body

Answer 7

ATP

Question 8

what does kinetics refer to?

Answer 8

how fast something will happen. thus, if you want to know how fast a rxn will go, you look at kinetic factors like transition state and activation energy.

Question 9

the higher the transition state (aka the higher the activation energy), the ____ (faster or slower) the rxn will occur

Answer 9

slower

Question 10

the energy difference between your reactants/reagents and your products is your ____

Answer 10

deltaG

Question 11

catalysts increase the rate of the rxn by _____ the transition state and reducing the ______ ______

Answer 11

stabilizing the transition state

reducing the activation energy

Question 12

why do catalysts not act in the thermodynamic region of the rxn and therefore do not affect deltaG?

Answer 12

because they cannot make a nonspontaneous rxn spontaneous; they can only make rxns happen faster.

Question 13

In order to be considered an enzyme, the enzyme must do what 3 things?

Answer 13

increase the rate of the rxn, not be used up in the rxn, and be specific for a particular rxn

Question 14

If an active site on an enzyme is negatively charged, what type of substrate will it bind to?

Answer 14

a positively charged substrate

Question 15

when an enzyme is turned “off,” it can be referred to as being in the ____ state

Answer 15

tense

Question 16

an enzyme in the on position is also referred to as being in the ____ state

Answer 16

relaxed

Question 17

what is the number one way to regulate enzyme activity?

Answer 17

phosphorylation (a type of covalent modification)

Question 18

what is the second most common way to regulate enzyme activity?

Answer 18

allosteric regulation (regulator binds to the allosteric site, which is any site on the enzyme that is not the active site)

Question 19

how are zymogens activated?

Answer 19

by proteolytic cleavage of one of its peptide bonds

Question 20

what does the feed forward mechanism refer to?

Answer 20

a lot of reactant will stimulate the rxn forward

Question 21

what is a V vs. S graph

Answer 21

looks at the affect of various concentrations of substrate on a constant concentration of enzyme

Question 22

V vs. S graph: If substrate concentration is substantially low and then doubled, what will the rate of product do?

Answer 22

it will also double

Question 23

V vs S graph: What is Vmax

Answer 23

signals the max production rate under those particular conditions shown on the graph (this is the point on the graph where the slope levels off)

Question 24

Vmax only depends on (or can be affected by) the ______ concentration and the type of ____ being used

Answer 24

enzyme, enzyme

Question 25

V vs S graph: What is Km?

Answer 25

the substrate required to reach 1/2 of Vmax, and can be related to level of affinity the enzyme has on its substrate

Question 26

If an enzyme has an increased affinity for its substrate, how will Km be affected?

Answer 26

Km will decrease

Question 27

Enzyme inhibition: distinguish between competitive, noncompetitive, uncompetitive, and mixed inhibition

Answer 27

competitive inhibitor: binds at the active site of the enzyme so the substrate can no longer bind onto the active site itself

non-competitive inhibitor: binds to the allosteric site; substrate can still bind to the enzymes active site, but the enzyme won’t be able to process or react with the enzyme

uncompetitive: binds to the allosteric site of the enzyme-substrate complex, which makes the substrate locked into that active site.

mixed inhibitor: can bind to the enzyme alone or the enzyme-substrate complex; can also sometimes change the active site, making it harder for the substrate to bind to the enzyme, if it can at all.

Question 28

How to competitive, non-competitive, uncompetitive, and mixed inhibition affect Vmax and Km?

Answer 28

competitive: Km increases, Vmax stays the same (because if you increase the substrate concentration high enough, it can out-compete the inhibitor)

non-competitive: Km stays constant, Vmax decreases

uncompetitive: Km decreases, Vmax decreases
mixed: Km varies, Vmax decreases

Question 29

what is the lineweaver-burk plot of V vs S?

Answer 29

a reciprocal (aka inverse) plot of V vs S

Question 30

V vs S Lineweaver-Burk Plot: the bigger the Vmax value, the _____ the y-axis intercept value will be on the reciprocal plot

Answer 30

smaller

Question 31

Lineweaver-Burk plot: For allosteric inhibition, Vmax is a smaller number on a regular V vs S plot, which means that it will intersect the y-axis at a ____ (higher or lower) value compared to the uninhibited rxn

Answer 31

higher

Question 32

Lineweaver-Burk Plot: The larger the value of Km, the more x-axis intercept value will be to the ____ (right or left) compared to the uninhibited rxn.

Answer 32

right

Question 33

Enthalpy (potential energy) is stored in _____ of molecules

Answer 33

bonds

Question 34

what is the kinetic energy component of the gibbs free energy equation?

Answer 34

(deltaT)(deltaS)

Question 35

Can the change of substrate concentration affect Vmax?

Answer 35

no

Question 36

An anti-substrate antibody would decrease concentration of substrate, which means there is less substrate that the enzyme can bind to. How would this affect Km and Vmax

Answer 36

Km would increase because the ability for the enzyme to bind to its substrate decreases, as there is less substrate to bind to. Vmax stays the same because the enzyme hasn’t lost it’s affinity for the substrate (remember Vmax is never altered by substrate concentration).