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BMS1. Enzymes (PATEL) > Enzymes Part 2 (Kinetics) > Flashcards

Enzymes Part 2 (Kinetics) Flashcards

1
Q

Endergonic Reaction

A
  • ΔG > 0
  • Non-spontaneous; requires input of energy
  • Products have higher free energy than the reactants
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2
Q

Exergonic Reaction

A
  • ΔG < 0
  • Spontaneous
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3
Q

How can an endergonic reaction be driven to move forward?

A

By coupling it with an exergonic (favorable) reaction

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4
Q

Main molecule utilized in enzyme coupled reactions:

A

ATP

  • adenine (nitrogenous base)
  • ribose (5 carbon sugar)
  • three phosphate groups
  • -3.5 total charge
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5
Q

ATP has a high energy phosphate bond. Removal of 1 phosphate group leads to ADP and gives off a considerable amount of energy.

What type of reaction occurs and how much energy is given off?

A
  • hydrolysis (a phosphate bond is cleaved)
  • ΔG = -30.5 kJ/mol
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6
Q

ATP + H2O → ADP + Pi

ΔG =

A

-30.5 kJ/mol

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7
Q

ADP + Pi → ATP

ΔG =

A

+30.5 kJ/mol

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8
Q

What is the molecular basis for the large amount of energy given of by the conversion of

ATP + H2O → ADP + Pi

A
  • Electrostatic repulsion between the three phosphates destabilizes ATP molecule.
    • ATP has -3.5 charge
    • ADP has -2.5 charge
  • After hydrolysis, an individual phosphate can be stabilized by resonance stabilization, which makes it more stable than its form in ATP.
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9
Q

Equilibrium is a state of:

A

maximum stability

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10
Q

A process is spontaneous and can perform work only when it is:

A

moving toward equilibrium

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11
Q

Reaction velocity versus [E]:

A
  • more enzyme = faster rate.
  • linear correlation
  • substrate has more enzyme to bind to, increases [ES], increases product formation.
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12
Q

Reaction velocity versus [S]:

A
  • rate increases asymptomatically with increasing [S]
  • Velocity initially increases linearly, but then stabilizes and becomes constant when all enzyme active sites are saturated.
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13
Q

If you want to increase Vmax, you need to increase:

A

[E]

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14
Q

E + S ⇔ ES ⇒ E + P

What is Km?

A
  • Michaelis Constant
  • Conversion of E + S ⇔ ES
  • reflects affinity for a substrate to an enzyme
  • Km = [S] at ½Vmax
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15
Q

E + S ⇔ ES ⇒ E + P

What is Kcat?

A
  • Rate of ES ⇒ E + P
  • (Kcat)([E]) = Vmax
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16
Q

(Kcat)([E]) =

A

Vmax

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17
Q

Michaelis Menten Equation

A
  • v = initial velocity at a given [S]
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18
Q

½Vmax =

A

Km

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19
Q

Lineweaver-Burk Plot Equation:

A
  • x-intercept = -1/Km
  • y-intercept = 1/Vmax
20
Q

Km only changes with:

A

pH and temperature

Does not change with [E] or [S]

21
Q

Numerically, Km =

A

[S] at ½Vmax

22
Q

Smaller the Km:

A
  • higher affinity of enzyme for substrate
  • “tighter ES binding”
23
Q

Larger the Km:

A
  • lower affinity of enzyme for substrate
  • “less tight ES binding”
24
Q

Vmax is linearly dependent on:

A

[E]

25
Q

Kcat only changes with:

A
  • pH and temperature
  • does not change with [E] or [S]
  • a constant
26
Q

Conceptually, Vmax is:

A

maximum velocity with which the enzyme can catalyze the reaction

27
Q

Conceptually, Kcat is:

A
  • kcat = (Vmax)([E])
  • turnover number of an enzyme reflecting the number of moles of substrates converted to products per sec per mol of enzyme
  • ES converted to E + P
28
Q

Higher the Kcat:

A
  • more product produced per second per mole of enzyme
  • “high turnover:
29
Q

Fastest way to regulate enzyme activity:

A
  • phosphorylation/dephosphorylation of the enzyme
  • most phosphorylation occurs on the serine, threonine, and tyrosine amino acids of an enzyme (all have -OH groups)
30
Q

Slowest way to regulate enzyme activity:

A

extracellular signalling

31
Q

Enzyme regulation by specific proteolysis:

A
  • irreversible
32
Q

The two types of enzyme inhibitors:

A
  1. irreversible
  2. reversible
    • competitive
    • uncompetitive
    • noncompetitive
33
Q

Irreversible inhibitors are:

A
  • molecules that covalently bind to an active site amino acid of the enzyme to inhibit the activity.
  • substrate analogs
  • Examples:
    1. penicillin
    2. sarin (nerve gas)
    3. aspirin
34
Q

Reversible inhibitors are:

A
  • molecules that bind reversibly to inhibit enzyme activity
  • Three kinds:
    1. competitive
    2. uncompetitive
    3. noncompetitive
35
Q

Competitive inhibitors:

A
  • reversible
  • bind to active site of enzyme, compete with the substrate for active site slots.
  • Km INCREASED, Vmax UNCHANGED
  • can be overcome by increasing [S]
36
Q

Noncompetitive inhibitors:

A
  • reversible
  • bind to a separate site of the enzyme (not the active site)
  • Km UNCHANGE, Vmax DECREASED
  • increasing [S] does not help since their is no competition for the active site
37
Q

Example of a competitive inhibitor:

A
  • statins
  • inhibit enzyme involved in cholesterol synthesis
38
Q

Transition State Analogs:

A
  • potent inhibitors
  • stable molecules that resemble geometric and/or electronic features of the highly unstable transition state
  • binding is often much tighter than the substrate because they fit all elements of the active site
39
Q

Allosteric Enzymes:

A
  • have two binding sites:
    1. active site (for substrate)
    2. allosteric site (for a noncompetitive inhibitor or effector)
  • all are oligomeric (>1 peptide sequence)
  • allosteric molecules do not resemble substrates
40
Q

V versus [S] curve of allosteric enzymes:

A
  • sigmoidal (S-shaped)
  • due to cooperative substrate binding
41
Q

The two equilibrium states of allosteric enzymes:

A
  1. R-state (active; strong substrate binding)
  2. T-state (inactive; weak substrate binding)
42
Q

Allosteric activators stabilize:

A
  • the R-state (active) of an allosteric enzyme
    • increases substrate binding
    • increases activity
43
Q

Allosteric inhibitors stabilize:

A
  • the T-state (inactive) of an allosteric enzyme
    • decreases substrate binding
    • decreases activity
44
Q

K-type Allosteric Inhibitor:

A
  • increase K0.5 (DECREASES AFFINITY)
  • no effect on Vmax
45
Q

K-type Allosteric Activator:

A
  • decreases K0.5 (INCREASES AFFINITY)
  • no effect on Vmax
46
Q

V-type Allosteric Inhibitor:

A
  • decreases Vmax
  • no effect on K0.5
  • no effect on affinity
47
Q

V-type Allosteric Activator:

A
  • increases Vmax
  • no effect on K0.5
  • no effect on affinity

BMS1. Enzymes (PATEL) (3 decks)

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