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MCC > Wk 2 TBL 4 Enzyme Kinetics > Flashcards

Wk 2 TBL 4 Enzyme Kinetics Flashcards

1
Q

What is the pyrimidine biosynthetic pathway?

A

Pyrimidine synthesis (cytosine, thymine, and uracil)

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2
Q

What does OMP decarboxylase (UMP synthase) do?

A

Removes a CO2 in the pyrimidine biosynthesis pathway from OMP to make UMP

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3
Q

What is unique about the OMP decarboxylase enzyme?

A

1/2 life of the reaction is > 78,000,000 years w/o the enzyme
W/ enzyme: 1/2 life is <0.02 s

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4
Q

What is special about the delta-ALA synthase?

A
  1. 1st step in heme synthesis, puts glycine and succinyl-CoA together to make ALA
  2. derivative of B6 needed at active site
  3. linked to X-linked sideroblastic anemia
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5
Q

What can often cure X-linked sideroblastic anemia?

A

High doses of vit B6

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6
Q

Why do high doses of vit B6 often work to cure X-linked sideroblastic anemia?

A

The cofactor B6 vitamin derivative that’s part of ALA synthase helps stabilize the structure to help it work well enough to keep the heme synthesis pathway operating

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7
Q

What happens at enzyme active sites?

A

Substrates bind to the enzyme active sites where chemical transformations occur to create the product

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8
Q

How do active site AAs work?

A

Often act as acids and bases in the reaction
-enzyme activity often very pH sensitive

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9
Q

What dicates the reaction specificity?

A

The active site structure

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10
Q

Why are cofactors or coenzymes often necessary?

A

Reactions req chem capabilities not available from AA so the cofactors and coenzymes provide them

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11
Q

What is enzyme catalysis?

A

lowering the free energy of the transition state
-enzymes alter the kinetics (rates) but NOT the thermodynamics (the equilibrium b/w substrates and products) of a reaction

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12
Q

What does k stand for?

A

kinetics/rate of reaction
kcat = rate with catalysis

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13
Q

What do interactions w/ enzymes do to the free energy of transition states?

A

Lower the free energy

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14
Q

Why could a fever potentially lead to hypoglycemia in a neonate?

A

The rate of chemical and enzyme-catalyzed reactions increases ~12% per increase in degrees C, so a fever -> increased metabolic rate

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15
Q

What is rate-limiting for a reaction?

A

Binding of a substrate

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16
Q

What is rate-limiting for a reaction?

A

Binding of a substrate

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17
Q

What shape is a saturation curve?

A

hyperbolic

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18
Q

Example of non-enzymatic reaction with different kinetics

A

HbA + glucose -> HbA1c
-linear reaction rate - as substrate increases, the rate of formation increases

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19
Q

Yente analogy to enzyme

A
20
Q

What happens to the max rate if more enzymes are recruited?

A

If double the enzymes, double the max rate (Vmax)

21
Q

What is the equation that fits a typical enzyme curve?

A

michaelis menten equation for hyperbolic curve:

22
Q

What is Vmax?

A

maximal velocity - rate no longer increases when it is saturated w/ substrate

23
Q

What is the Km?

A

substrate concentration that gives 1/2Vmax
=approx measure of the affinity for an enzyme for its substrate
-lower concentrations -> tighter binding
-independent of enzyme concentration

24
Q

What values change w/ changed enzyme concentration?

A

Vmax but not Km

25
Q

When is the rate of reaction most sensitive to changes in [substrate]?

A

Below Km
-the curve is steeper

26
Q

The rate sensitivity to [substrate] changes has caused what to evolve regarding enzymes?

A

To have Km values > the physiologic [substrate]

27
Q

What is the kcat?

A

Turnover rate for an enzyme
=product/time
-value is independent of [enzyme] present in a reaction or cell
-a per enzyme molecule rate (=#marriages each Yente can arrange per year)

28
Q

What values does enzyme concentration affect?

A

Vmax but not kcat

29
Q

What are 2 common mechanisms for enzyme regulation other than by gene expression?

A
  1. post-translational modification
  2. reversible binding of activators or inhibitors
30
Q

What is a competitive inhibitor?

A

Compete w/ substrate for binding
-Vmax stays same (w/ high enough [substrate], enzyme can still achieve same max rate
-Km increases b/c takes more substrate to get to 1/2Vmax

31
Q

What would the double-reciprocal plot of competitive inhibition look like?

A
32
Q

What does the slope of double reciprocal plot look like?

A

slope = Km/Vmax

33
Q

What is the intercept of a double-reciprocal plot?

A

intercept = 1/Vmax

34
Q

What does the double reciprocal plot look like w/ competitive inhibitor?

A

lines Cross = Competitive inhibitor

35
Q

What happens to enzyme kinetics when noncompetitive/uncompetitive inhibitors bind?

A

Vmax ALWAYS decreased
Km may or may not be affected

36
Q

What is a chemically stable analog of a tansition state?

A

An inert molecule that does not react with the enzyme even though it has binding interactions like the transition state
=competitive inhibitors

37
Q

Summary

A
38
Q

What is the transition state?

A

the most unstable or high energy state along the reaction pathway

39
Q

Do catalysts/enzymes alter the equilibrium of a reaction?

A

No b/c they are regenerated after each reaction cycle

40
Q

What is the major source of free energy used to lower the activation energy barrier?

A

Binding energy, which is free energy released from interactions b/w substrates and enzymes in the complex with weak, noncovalent bonds

41
Q

What are active sites most complemetary to?

A

The transition states of the reactions they catalyze, not the substrates directly

42
Q

Besides activation energy, what else can enzymes affect?

A

They can reduce the entropy that substrates must overcome to form a product
-binding energy holds the substrates in the proper position

43
Q

At what temp do enzymes typically begin to unfold?

A

45 degrees C

44
Q

What is the reaction rate increase with enzymes for each 1 degree C increase?

A

~10%

45
Q

How are steady-state kinetics performed?

A

Use a small (and constant) concentration of enzyme and measure how fast product is formed when differing concentrations of substrates are used.
-Generates a rate vs [substrate] curve

46
Q

Why are steady-state kinetics performed?

A

To understand how enzymes fxn and what happens when someone inherits a genetic variant in a gene encoding an enzyme

47
Q

How do rate vs [substrate] curves compare with and w/o enzymes?

A

curvilinear vs linear

MCC (44 decks)

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