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EOM 1 - Test 1 > Lecture 12: Kinetics > Flashcards

Lecture 12: Kinetics Flashcards

Enzyme Kinetics I

1
Q

What role do enzymes have in:

Keq

ΔG

Ea

A

Keq - No Effect

ΔG - Decrease

Ea - Decrease

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2
Q

Are enzymes produced or consumed by reactions which they catalyze?

A

No, Catalysts are neither produced or consumed by reactions.

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3
Q

Zero Order:

Rate of Reaction Independent of:

Depending on:

Commonly seen on M-M Plot?

A

Independent of [S]

Depending on other factor–pH, Temp

As the slop approaches Vmax

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4
Q

First Order:

Proportional to:

Commonly Seen on M-M Graph:

A

Rate is proportional to [S]

The early climbing stage of M-M plot

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5
Q

Second Order:

Proportional to:

How do we usually handle this biologically, and why?

A

Proportional to [S1] and [S2]

If [S2] is >>> [S1] , [S1] will be rate limiting step, and we ignore [S2] ; commonly this is water in a biological approach

Treat as First Order

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6
Q

How do you calculate Km from a M-M plot or series of numbers?

How do you calculate Vmax?

A

Km = 1/2 Vmax

Vmax = Asymptote which graph approaches (or number if given table of values)

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7
Q

What is the rate limiting step in First Order kinetics?

Zero Order?

A

Collision of Substrate with Enzyme (there are open enzymes available)

Product Release from Enzyme (enzyme fully saturated)

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8
Q

What is the x-intercept on a Lineweaver Burk Plot?

What is the y-intercept on a Lineweaver Burk Plot?

What is the X-axis?

Slope?

A

X-intercept = -1/Km

Y-intercept = 1/Vmax

X-axis = 1/[S]

Slope = Km/Vmax

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9
Q

Which will have greater binding, a small Km or large Km?

A

Small Km = Tight Binding

Large Km = Weak Binding

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10
Q

What approximates the physionlogical concentation of true substrate in many cases?

A

Km

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11
Q

How would you determine which substrate has a higher affinity for a substrate given two enymes plotted on a M-M plot?

A

The smaller Km will have a higher affinity

(Km=1/2 Vmax)

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12
Q

How would you determine which substrate binds best when given a table including an enzyme, multiple substrates, and Km values?

A

The lowest Km has the highest affinity

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13
Q

What is the number of substrate molecules converted to product per enzyme molecue per unit time?

A

kcat

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14
Q

Which is a better enzyme, a large kcat or a small kcat?

A

Large Kcat = better enzyme

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15
Q

In living cells, are enzymes usually saturated?

A

No

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16
Q

How would you mathematically determine the “best” enzyme in a living cell given the following:

Why is the rate usually <<< k2K

A

Largest Ratio of k2 / Km

[S] usually < Km

17
Q

Enzymes reaching what specificity constant value are considered “perfect”?

A

108

18
Q

What is the specificity constant of an enzyme?

A

kcat / Km

19
Q

How do enzymes vary with temperature?

At what T does full denaturation usually occur?

What is the optimum tenperature for most enzymes?

A

Activity usually doubles w/ 10oC increase

Denatured at 70oC

~ 30oC

20
Q

In Single-Displacement reactions, what must occur before catalysis can proceed?

In Double-Displacement (ping-pong), what must occur for catalysis to proceed?

A

Both Substrates must combine with the enzyme

One or more products are released from the enzyme before all substrates are added

21
Q

On a Lineweaver-Burk Plot, what will the following plots be?

Single Displacement

Double Displacement (ping pong)

A

Several non-parallel lines, intersecting at a Ternary Complex

Parallel lines

22
Q
A
23
Q

What are the classes of Reversible Inhibitors?

What are Irreversible Inhibitors? Examples?

A

Reversible: Competitive and Noncompetitive Inhibitors

Irreversible: Covalent, permanent modification. Examples include antibiotics, which block bacteria cell walls.

24
Q

What effect on Vmax and Km do Competitive Inhibitors have?

Why? Can this be overcome?

What will be the appearance of Competitive Inhibition on a Lineweaver-Burk Graph?

What will be the appearance of Competitive Inhibition on a MM-plot?

A

Km - Increase

Vmax - No Change

Inhibitor competes with substrate for binding site, at infinite [S], Inhibitor has no effect.

Lineweaver Burk: Non parallel lines intersecting at the y-intercept, or 1/Vmax

M-M Plot: Similar shape, with increased Km

25
Q

What effect on Vmax and Km do Nonompetitive Inhibitors have?

Why? Can this be overcome?

What will be the appearance of Noncompetitive Inhibition on a Lineweaver-Burk Graph?

What will be the appearance of Noncompetitive Inhibition on a MM-plot?

A

Km - No Change

Vmax - Decrease

Inhibitor binds at site other than active site, no matter increase in [S], inhibitor can still bind to enzyme.

Lineweaver Burk: Non-parallel lines that intersect at the x-intercept (-1/Km)

M-M Plot: Similar shape with a reduced Vmax, but no change to Km

26
Q

What effect on Vmax and Km do Mixed Inhibitors have?

Why? Can this be overcome?

What will be the appearance of Mixed Inhibition on a Lineweaver-Burk Graph?

What will be the appearance of Mixed Inhibition on a MM-plot?

A

Km - Can Increase or Decrease

Increase: Inhibitor Favors Binding to Free Enzyme (like competitive)

Decrease: Inhibitor Favors E-S Complex (like uncompetitive)

Vmax - Decrease

Lineweave Burk: Will depend on the case above, Vmax will decrease, however Km can increase or decrease

M-M Plot: Decreased Vmax, Km increase or decrease

27
Q

What substance is the inhibitor Methotrexate similar to?

What type of Inhibitor is this?

What would be expected for Vmax and Km?

A

Folic Acid

Competitive Inhibutor

Km: Increase

Vmax: No Change

28
Q

What is the function of the inhibitor Arsenite?

What type of inhibitor is this?

What is the effect on Km and Vmax?

A

Arsenite blocks the catalytic activity of lipoamide containing enzymes, such as PDH

Noncompetitive Inhibitor

Km: No Change

Vmax: Decrease

29
Q

What is the function of the inhibitor Statin?

What do these inhibit?

What type of inhibitor are these?

What will be the effect on Km and Vmax?

A

Statins inhibit cholesterol biosynthesis by inhibiting HMG-CoA Reductase. Accomplish by blocking active site due to similar molecular presentation.

Competitive Inhibitor

Km: Increase

Vmax: No Change

30
Q

What is the role of the inhibitor Fluorouracil?

What type of inhibitor are these?

A

Inhibit thymidylate synthase, used to treat solar keratoses and skin cancer

Inhibits FdUMP as an irreversible inhibitor

31
Q

If an inhibitor resembles the structure o the substrate, what type of inhibitor is it likely?

A

Competitive

32
Q

If presented with “covalent bonding” what type of inhibition is usually indicated?

A

Irreversible

EOM 1 - Test 1 (16 decks)

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