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Biochem > Enzymes > Flashcards

Enzymes Flashcards

1
Q

Enzymes are…

A

biological catalysts that are unchanged by the reaction they catalyze

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2
Q

Enzymes act by…

A

stabilizing the transition state

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3
Q

Enzymes have…

A

an active site (site of catalyst)

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4
Q

Exergonic reactions…

A

release energy; delta G is -

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5
Q

Enzymes do not…

A

alter the free energy (delta G) or enthalpy (delta H)

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6
Q

Lock and Key Theory

A

the enzyme and substrate are complementary

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7
Q

Induced Fit Model

A

the enzyme and substrate undergo conformational changes to interact fully

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8
Q

Some enzymes require…

A

metal cation cofactors or small organic coenzymes to be active

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9
Q

The large rate accelerations of enzymes…

A

correspond to large decreases in the free energy of activation for the reaction

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10
Q

All reactions…

A

pass through a transition state on the reaction pathway

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11
Q

The active sites of enzymes…

A

bind the transition state of the reaction more tightly than the substrate

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12
Q

The catalytic role of an enzyme…

A

is to reduce the energy barrier between substrate (S) and transition state (X)

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13
Q

Rate acceleration by an enzyme means…

A

that the energy barrier between ES and EX must be smaller than the barrier between S and X

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14
Q

Enzyme catalyzes reactions by…

A

lowering the activation energy

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15
Q

For a given energy of EX, raising the energy of ES will…

A

increase the catalyzed rate

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16
Q

Raising energy will be accomplished by

A

loss of entropy due to formation of ES

destabilization of ES

17
Q

Destabilization of ES by…

A

strain, distortion, desolvation

18
Q

How does destabilization of ES affect enzyme catalysis

A

catalysis does not occur if ES and X are equally stabilized; catalysis will occur if X is stabilized more than ES

19
Q

Formation of the ES complex results in…

A

entropy loss

20
Q

Substrates typically lose waters of hydration in the formation of…

A

the ES complex

21
Q

Electrostatic destabilization of a substrate…

A

may arise from juxtaposition of like charges in the active site

22
Q

How tightly do transition-state analogs bind to the active site?

A

very tight binding (10^-20 to 10^-26)

23
Q

Enzymes are often targets for…

A

drugs and other beneficial agents

24
Q

Transition state analogs often make…

A

ideal enzyme inhibitors

25
Q

What are the mechanisms of catalysis?

A

covalent catalysis; general acid-base catalysis; low barrier hydrogen bonds; metal ion catalysis

26
Q

Enzymes facilitate formation of…

A

near attack conformations

27
Q

Protein motions are essential…

A

to enzyme catalysis

28
Q

Proteins are constantly moving…

A

bonds vibrate, side chains bend and rotate, backbone loops wiggle and sway

29
Q

Enzymes depend on protein movement to…

A

provoke and direct catalytic events

30
Q

Active site conformation changes can…

A
  1. ) assist substrate binding
  2. ) bring catalytic groups into position
  3. ) induce formation of NACs
  4. ) assist in bond making/ breaking
31
Q

Catalysis in enzymes active sites depends on…

A

motion fo active site residues

32
Q

Covalent catalysis

A

enzymes derive much of their rate acceleration from formation of covalent bonds between E and S

33
Q

The side chains of amino acids in proteins offer a…

A

variety of nucleophilic centers for catalysis

34
Q

The covalent intermediate can…

A

be attacked in a 2nd step by water or a 2nd substrate

35
Q

Specific acid-base catalysis

A

involves H+ or OH- that diffuses into the catalytic center

36
Q

General acid-base catalysis

A

involves acids and bases other than H+ and OH-

37
Q

typical H-bond strength

A

10-30kJ/mol

38
Q

Low-barrier hydrogen bonds

A

pKa values of the two electronegative atoms must be similar/ energy released can assist catalysis

39
Q

Residues may function in secondary roles in the active site:

A
  1. ) raising or lowering catalytic residue Pka
  2. ) orientation of catalytic residues
  3. ) charge stabilization
  4. ) proton transfers via hydrogen tunneling

Biochem (11 decks)

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