Lecture 12

Question 1

What is significant about studying kinetics?

Answer 1

it helps fully understand what is going on in a reaction we need to know

Question 2

If the reaction will occur =
How long will the reaction take =
How will the reaction occur =

Answer 2

If the reaction will occur = THERMODYNAMICS
How long will the reaction take = KINETICS
How will the reaction occur = MECHANISM

Question 3

What does kinetics tell us about enzymes?

Answer 3

important aspect to how they work
-enzymes do not create new chemistry, they just make it occur faster

Question 4

If living systems are not at equilibrium (parts may be), then what are they at?

Answer 4

often a steady state
-a balance of reactions creating and destroying compounds

Question 5

What is thermodynamics about, and what does it say about rate?

Answer 5

It is about stability
It says nothing about rate

Question 6

In thermodynamics, what does the free energy law tell us?

Answer 6

tells you if a reaction is favorable

NOTHING ABOUT RATE

Question 7

What are catalysts?

Answer 7

enzymes that increase reaction rates

Question 8

Kinetics is about what?

Answer 8

rates

Question 9

What is the Arrhenius equation?

Answer 9

k = Ae^-Ea/RT

Question 10

What does the Arrhenius equation show?

Answer 10

shows that the rate of a reaction (k) is inversely proportional to (Ea) the activation energy

Question 11

Rates are about what?

Answer 11

mechanics

Question 12

What is rate limited by?

Answer 12

limited by the stability of the Transition state relative to the reactions

Question 13

What do enzymes do to forward and reverse reactions?

Answer 13

they increase the rate of each, thus the equilibrium does NOT change

Question 14

What is the enzyme mechanism?

Answer 14

a chemical model describing how an enzyme reduces Ea (activation energy)

Question 15

What is the order of chemical reactions?

Answer 15

the forward rate constant (k1) dependence on S

Question 16

Zero order

Answer 16

rate does NOT depend on S

Vo = K1

Question 17

1st order

Answer 17

rate depends ONLY on S

Vo = k1[S1]

Question 18

2nd order

Answer 18

rate depends on BOTH S1 and S2

Vo = k1[S1][S2]

Question 19

In first order reaction, how do you find the reverse rate constant?

Answer 19

If you know forward rate constant (k1) and Keq then you can calculate.

Keq = k1/k-1 = P/S

Question 20

In order to find the forward rate in a second order reaction, you must find the concentrations of BOTH substrates which becomes difficult.

So what do you do to find the forward rate?

Answer 20

convert to a first order problem by making the reaction pseudo first order

Question 21

What has to be true of A or B for the reaction to be considered pseudo first order?

Answer 21

if either A or B remain constant as the reaction proceeds

Question 22

How can pseudo first order be achieved?

Answer 22

by increasing one substrate to saturating concentrations then varying the other

Question 23

In a pseudo 1st order reaction, what will the rate depend upon?

Answer 23

the limiting substrate

Question 24

If the rate equation (plot) is linear, what is true?

Answer 24

the rate increases only with S1

Question 25

What two men INDEPENDENTLY described the first kinetic model for an enzyme? What did they study?

Answer 25

Adrian Brown Viktor Henri invertase

Question 26

What does invertase do, and what is it important for?

Answer 26

converts sucrose to glucose and fructose important for brewing beer

Question 27

Who was a professor of Malting and Brewing?

Answer 27

Adrian Brown

Question 28

What did Henri find?

Answer 28

at saturating [S], the rate (Vo) increases linearly with increasing [E] reaction is pseudo-first order with respect to [E]

Question 29

When there is an enzymatic second-order reaction and [E] is varying, what does the graph look like?

Answer 29

linear

Question 30

When there is an enzymatic second-order reaction and [S] is varying, what does the graph look like?

Answer 30

curved

Question 31

Pictured is a Varying [S] reaction curve: What does the bottom left arrow mean? What does the top right arrow mean?

Answer 31

1) first order with respect to S 2) zero order with respect to S--means at high [S] the rate does not depend on [S]

Question 32

In and enzymatic second-order reaction and [S] is varying, what is this the hallmark behavior of?

Answer 32

a saturated catalyst

Question 33

In Henri's chemical model that explains enzymes, what is Vmax?

Answer 33

fastest rate that the enzyme can turnover (make product)

Question 34

What is the formula for Henri's chemical model?

Answer 34

Vo = Vmax[S] / b + [S] b = Km Km = [ES] / [E] [S] = k1/k-1

Question 35

What is Km on Henri's. chemical model?

Answer 35

it is equivalent to half of the V max but on the [S] x axis

Question 36

If Km isn't the ES affinity constant, and isn't the ES dissociation constant, then what is it?

Answer 36

the stability of the ES complex

Question 37

In Henri's model, what did the larger Km (affinity) suggest?

Answer 37

slower enzyme

Question 38

What did Michaelis and Menten redefine Km as?

Answer 38

as the ES dissociation constant

Question 39

According to Michaelis and Menten's approach, what is the new Km formula?

Answer 39

Km = [E] [S]/[ES] = k-1/k1

Question 40

What does Km correctly represent, and who figured this out?

Answer 40

the stability of the ES complex Briggs and Haldane

Question 41

SO, what is the correct Km formula?

Answer 41

Km = k-1 + k2 / k1

Question 42

What should stability in relation to the ES complex be defined as?

Answer 42

the rate dissociation of ES complex divided by the rate of formation of the ES complex

Question 43

Assuming all of [E] is in the ES complex, it is what?

Answer 43

saturated at very high [S]

Question 44

What does Vmax mean, and what are the two formulas that can be used?

Answer 44

fastest rate that the enzyme can Vmax = K2 [E] total or Vmax = Kcat [E] total

Question 45

In this formula: Vmax = Kcat [E] total What is Kcat?

Answer 45

the rate constant of the rate-limiting step Kcat=K2

Question 46

Vmax / [E] total = Kcat = turnover number (s^-1)(when sat'd) What does this mean?

Answer 46

the number of moles of substrate converted per second the catalytic constant for the rate limiting step

Question 47

How do you find the time for a single catalytic event?

Answer 47

1 / Kcat

Question 48

What does Kcat = ?

Answer 48

Kcat = turnover number (s^-1) moles of substrate converted per second

Question 49

Kcat / Km = what? (in words)

Answer 49

How fast the ES makes product / How easily ES forms

Question 50

In the classical competitive inhibition, what occurs?

Answer 50

the substrate and inhibitor compete for same site