Enzymes Lecture 2

Front 1

what are the 2 possible mechanisms of binding substrates to active sites? which one is thought be more correct?

Back 1

lock and key - everything is excat. no room to change

induced fit - the enzyme is not so rigid; contains binding or recognition sites which the substrate binds to and the enzyme undergoes a conformation change to fit the substrate.

Front 2

what are the 3 ways pH affects the reaction velocity?

Back 2

1. enzymes have a pH optimun for catalytic activity; not all the same
2. the pH can affect the ionization of the active site if there are chemical groups that are required to be in an ionized or unionized state. can do the same for the substrated ionization state

Front 3

what are the 2 ways temperature affects the reaction velocity?

Back 3

1. the temperature can increase the velocity by increasing the numbers of molecules having sufficient energy to reach the activation barrier to form products. (basically lowers the free energy of the substrate)

2. it can decrease the velocity by denaurating the enzyme

Front 4

how does enyzme concentration affect the reaction?

Back 4

the rate of an enzyme catalyzed reaction is directly proportional to the concentration of the enzyme; there must be sufficient substrate to saturate all the enzymes.

The curve for this with Velocity as the Y and [E] as the x will be a 1 to 1 line. 45 degrees if you will

Front 5

What are 2 ways the substrate concentration affects the reaction velocity?

Back 5

1. the rate of the enzyme cataluzed reaction increases with substrate concentration until a maxium velocity is reached
2. the leveling off of the reaction velocity speed relects the saturation with substrate of alailable binding sites on the enzyme

Front 6

What happens when there is low [S]?

Back 6

the reaction is a first order reaction which means the rate is directly proportional to the [S].

Front 7

what happens when [S] is very high?

Back 7

the reaction shows saturation; at high [S] the velocity no longer increases with increasing [S]; the reaction now is a zero order reaction

Front 8

what is vmax?

Back 8

v max is the reaction velocity at an infinite [S].

Front 9

how do you define Km

Back 9

the [S] that gives a reaction velocity = 1/2 Vmax.

Also known ass the Michaelis Constant

Front 10

What is the Michaelis-Menten Equation?

Back 10

V =( Vmax * [S] ) / ( Km + [S] )

Front 11

What are the three assumptions to the michaelis menten equation?

Back 11

1. the concentration of the enzyme is very small comppared to the concentration of the substrate
[E] <<< [S]

So: [E] = [Et] - [ES]

2. the reaction occurs at steady state. [ES] does not change with time;

3. only initial reaction volumes are used; at this time the concentration of the product is very small and the rate of the back reaction from P to ES can be ignored.

Front 12

What does it mean to have a high Km?

Back 12

a High Km mean the substrate has a low affinity for the enzyme.

Front 13

what does it mean to have a low Km?

Back 13

a low Km means that the substrate wants to bind to the enzyme; basically S loves E so so much. :)

Front 14

So CH3CHO is a bad intermediate product in the breakdown of EtOH;
The enzyme that breaks it down is ALDH; if you have a low Km value for this reaction is that good or bad? if you have a high Km value for this reaction is that good or bad?

Back 14

a low Km value is good bc it means that you will not accumulate CH3CHO; a high Km value is bad because CH3CHO will not bind to the enzyme and therefore will not be broken down very quick. this happens because of a mutation. A Lys (+) is replaced by Glu (-)

Front 15

is Km constant for a reaction? What are the units of the Km?

Back 15

yes. Km is constant for a reaction. the units are moles / liter

Front 16

what is Kcat? How do you calculate it?

Back 16

Kcat is the turnover number; the turnover number or the number of molecules of substrate converted to product per enzyme molecule per second. It is calculated by K3 = Vmax / [Et]

Front 17

for teh Lineweaver-Burk Plot what does each of the following values =
y = mx + b;

What are the x and y intercepts equal to?

Back 17

y is 1/V
x is 1/S
m is Km/Vmax
b is 1/Vmax

X intercept = - 1/Km
Y intercept = 1/Vmax

Front 18

in the Eadie Hofstee Plot what kind of line do you get, what is plotted against what? what is the slope equal to? what is the y-intercept?

Back 18

it is a negative slope lline. the velocity (y) is plotted againts V/[S]. The slope is equal to -Km. the y intercept is Vmax

Front 19

What are irreversible enzyme inhibitors? What is an example?

Back 19

an irreversible enzyme inhibitor occurs when ann inhibitor covalently binds to the enzyme or binds so tightly it is not released. An example is nerve gas DFP - which binds to acetylcholinesterase and does not allow acetylcholine to be broken down as a result it accumulates and makes the nerve go into a constant contraction phase

Front 20

how do resersible enzyme inhibitors work?

Back 20

they bind to enzymes through non - covalent bonds - dilution of the enzyme inhibitor complex results in dissociation of the reversibly bound inhibitor and recovery of the enzyme activity; 2 types competitive and non-competitve

Front 21

How does a competitive inhibitor work? How can it be overcome? Does Vmax change with a competitive inhibitor? What does a competitive inhibtor do the Km value?

Back 21

It works by looking like the substrate and binding to the same active site as the substrate.
It can beovercome by adding more substrate
The Vmax does not change - because of high [S].
Km value goes up because more substrate is needed to reach 1/2 Vmax

Front 22

On a lineweaver-burk plot what will the different lines look with / or without a C.I.

Back 22

both lines will show different x-axis intercepts. As the [CI] goes up the x-axis intercept will move to the left. this is because the x-axis intercept is equal to -1/Km. However, they will both have the same y-axis intecept because they both will have the same Vmax

Front 23

Is it possible to get the E bound to the Substrate bound to the Competitive inhibitor?

Back 23

No, becasue the S and I both bind to the same active site.

Front 24

what will the traditional graph look like for a competive inhibitor enzyme reaction?

Back 24

the new line will be below the graph that does not have the CI, The Km value will be larger.

Front 25

what will the eadie-hofstee graph look like with a competitive enzyme reaction?

Back 25

the slope of the line will be different because slope is equal to -Km. The y intercept will be the same because Vmax is the same for both reaction. Since the velocity is different the line will be steeper pointing down closer to the orgin. as the [CI] goes up the line intersects the x axis closer and closer to the origin

Front 26

How does a noncopetitive inhibitor work?
what does Vmax do?
What does Km do?

Back 26

-they bind to the enzyme but not in the same spot as the substrate.
-they can bind to the free or substrated bounded enzyme
-may prevent necessary conformational change in the enzyme
-Vmax goes down even with very high [S]
- Km is unchanged

Front 27

what does the lineweaver - burk plot look like for a non competitive inhibitor?

Back 27

will have the same x-axis intercept because the Km values are the same, however will have different y- axis intercepts because the vmax are different. because here the y-axis intercept is 1/Vmax, the line will be higher compared to the reaction that does not have an NCI. The line gets steeper and steeper as you increase the [NCI]

Front 28

what does the traditional graph of the NCI ?

Back 28

the curve for the NCI is lower than the line for the reaction - the I. i.e. vmax is different but Km is the same.

Front 29

What does the Eadie-Hofstee graph look like with a NCI?

Back 29

bc the Km values are the same it means that the slopes are the same however, since the the Vmax are different the y axis intercepts are different. as the [NCI] goes up

Front 30

What is ethylene glycol? What does it do the body?

Back 30

Both Ethylene Glycol and EtOH are metabolized by the same thing, howevev ethylene glycol is turned into Oxalic Acid which is toxic; If pt has ethylene gylcol then give the pt EtOH to compete for the active site of ADH which prevents ethylene gylcol from turning into oxalic acid

Front 31

First how do sulfa drugs work?

Back 31

Sulfa drugs work by taking advantage of the fact that bacteria have to make folic acid from three things. Sulfa drugs have a molecule that looks like one of the substrates used by the molecule. So a sulfa drug is an example of a competivie inhibitor

Front 32

Just for your knowledge

Back 32

many commonly prescribed drugs are enzyme inhibitors;

ACE is used to convert angiotensis I to angiotensin II which causes blood vessels to constrict.