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Bchem 393 > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

Equation for reaction rate and units of k for 1 and second order reaction

A

V=K[reactants]

K= 1/s

K=1/MS

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2
Q

What does a pseudo first order reaction mean

A

One of the reactants is much lower concentration than than the other so the reaction rate doesn’t depend on the lower one

A»»B

A is only included in calculation

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3
Q

What is a zero order reaction

A

The reaction doesn’t depend on the concentration of reactants

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4
Q

What is initial velocity

How does it get simplified

A

The moles of product formed per second

The early measurement when time is around 0 and product is around 0

Because of this we can assume [products] is negligible and take it out of the equation to simplify

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5
Q

What happens to initial velocity when conenctrstion of substrate increses

A

The intially velocity is higher

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6
Q

What is the value of Km

A

K-1 + k2 / k1

Or the x axis value at Vmax/2

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7
Q

What does the michealis mean ten plot assume

What does this mean

A

Assume steady state kinetics

The initial velocity is measured while the [ES] (enzyme substrate complex) is relatively stable (constant, meaning the rate of the ES formation = rate of ES breakdown)

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8
Q

What is maximum velocity

A

Measured When all the enzyme is bound to the substrate so that [ES] = [E] total

It’s directly dependent on enzyme concentration

Vmax = K2 • [E]t

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9
Q

On the part of the graph where [S] is much less than Km what happens to initial velocity

A

V0= Vmax([S]/Km)

The initial velocity becomes directly proportional to the [S]

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10
Q

On the part of the graph where [S] is much greater than Km what happens

A

V0= Vmax

The rate is zero order and independent of [S]

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11
Q

On the part of the graph where [S] is equal to Km what happens

A

V0 = Vmax / 2

km is equal to [S] when the reaction rate is at 1/2vmax

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12
Q

What is Km and what does it depend on

A

The concentration of substrate where half the enzymes molecules are bound to the substrate

Depends on the type of substrate, ph, temp, ionic strength, type of enzyme

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13
Q

The cellular concentration of a substrate is usually close to what

How does this help

A

The Km value

This is the point where we have a significant velocity and any small changes up and down in substrate concentration will change the velocity significantly

Sensitive area

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14
Q

What are the two ways to determine km and Vmax

A

Nonlinear regression analysis

Lineweaver burk plot

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15
Q

What is a non linear regression analysis

A

You do an experiment an make the michealis menten plot, then put is into a computer system with the equation that the plot gave you

The computer tests values of km and v max that will make the calculated data best fit the experimental data

Fastest and accurate way to find km and Vmax

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16
Q

What is a lineweaver burk plot

A

Take the inverse of the menten equation (v0= Vmax (s/s+km))

This gives equation in the form of
y=mx + b

The x intercept is -1/km
Y int is 1/vmax

Can find the Vmax and km from the
X and y intercepts

Less reliable because taking reciprocal of larger values

17
Q

What is the turnover number

A

Kcat

The number of substrate molecules that the enzyme can convert to product per unit time ONLY when the enzyme is fully saturated with substrate

For ex. If enzyme has kcat value of 500 per second that means the enzyme can take 500 molecules of the substrate per second and turn them each into product

When under these saturated condition we are operating under Vmax

The k2 in the Vmax equation becomes kcat

Kcat=vmax/[E]t

18
Q

How do you find the amount of time a reaction takes place for kcat

A

1/kcat give amount of time for a single reaction

19
Q

Catalytic efficiency : If we want to include kcat in our v0 equation what do we do

A

Substitute Vmax in the v=0 equation for kcat • [E]t

20
Q

Catalytic efficiency : When [S] «< Km what happens

A

V0= (kcat/km) [S] • [E]t

The concentration of E is about equal to the total e concentration

21
Q

What is kcat/km

A

The rate constant for ES formation

Is called the specificity constant and measures the catalytic efficiency because it takes into account the rate of catalysis (kcat) and the nature of the enzyme/substrate interaction (Km)

Shows enzymes preference for substrate, if higher more prefer

22
Q

What is chemotrypsin

A

A type of enzyme protease that cleaves next to bulky hydrophobic (nonpolar) side chains

Has a higher kcat/km value for phenylalanine meaning the enzyme is good a turning substrate to product

23
Q

Kcat/km is always Less than

A

K1

24
Q

What happens if the rate of product being formed (kcat) is much greater than the dissociation of ES (k-1)

A

The kcat/km is close to k1

25
Q

What is k1

A

The rate constant for the formation of the enzyme substrate complex

The rate limiting step for how efficient the enzyme is going to be

26
Q

What is the diffusion controlled rate of encounter

A

The thing that limits the catalytic efficiency, how fast the enzyme can collide with/encounter the substrate in solution

10^8-10^9 is best

If the kcat/km is close to the rate of encounter the enzyme is kinetically perfect

27
Q

How do temp affect enzyme activity

A

The activity increases with higher temps but eventuallyy get denatures and stop working

28
Q

What is tyrosinase

A

Example of how temp affect activity

The the temp on a cat is lower the colour of fur is darker since enzyme is working better

If temp is higher the enzyme is denature and white fur happens

29
Q

What is the optimal ph for pepsin

Chemotrypsin

A

1.5

8

30
Q

How does Ph affect enzyme activity

A

Depending on the ph of where the enzyme is, the side chain amino acid residue in the enzyme with be deperotonated or protonated

The optimal activity would be at the peak of the curve

Bchem 393 (31 decks)

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