Chapter 11 Enzyme Catalysts Flashcards

1
Q

•What are single displacement and double displacement bimolecular reactions?

A

Bimolecular Reactions
■ Typically have 2 (or more) substrates
■ Bisubstrate reactions have unique rate equations
– Single-displacement / Sequential
■ Ordered:
-Leading substrate binds first
-Ordered release of products
■ Random:
-Substrates can bind in any order
-Products released in any order
■ Double Displacement (Ping-pong):
-Product of the first reaction is released prior to the binding of the
second substrate
-Forms a covalently modified enzyme intermediate, F

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2
Q

o What is the function of Oxidoreductases?

A

Catalyze Oxidation-reduction reactions

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3
Q

o What is the function of Transferases?

A

Catalyze Transfer of functional groups reactions

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4
Q

What is the function of Hydrolases?

A

Catalyze Hydrolysis reactions

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5
Q

What is the function of Lyases?

A

Catalyze Group elimination to form double bonds

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6
Q

What is the function of Isomerases?

A

Catalyze Isomerization

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7
Q

What is the function of Ligases?

A

Catalyze Bond formation coupled with ATP hydrolysis

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8
Q

•What is the catalytic site, binding site, exosites of an enzyme?

A
  • The active site consists of amino acid residues that form temporary bonds with the substrate (binding site) and residues that catalyze a reaction of that substrate (catalytic site)
  • An exosite is a secondary binding site, remote from the active site, on an enzyme or other protein
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9
Q

•What are the general properties of enzymes and how do enzymatic reactions compare to chemical reactions?

A

General properties
-Rate Enhancement
■ Catalytic power (rate enhancement) - the ratio of the enzyme-catalyzed rate of a reaction to the uncatalyzed rate
-Specificity
■ Geometric and electronic
complementarity
– Lock and key
– Induced fit
Stereospecificity
■ May identify prochiral molecules
Some enzymes are less specific for substrate specificity and reaction type
– Exception to the rule (in picture)

Differ from chemical reactions
■ Higher reaction rates
■ Use milder reaction conditions
■ Reaction specificity
■ Tightly regulated

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10
Q

How do you calculate the catalytic power of an enzyme?

A

Look at video and practice everytime you get this card

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11
Q

• Define and recognize cofactors (metal ions, coenzymes, cosubstrates and prosthetic groups)

A

Cofactors basically act as an enzymes’ “chemical teeth”
-Metal ions- Cu2+, Fe3+, Zn2+ (if Cd2+ or Hg2+ replace Zn renders enzyme inactive)

Coenzymes

-cosubstrates(NAD+ and NADP+) and prosthetic groups (are permanently associated with their protein, often by covalent bonds,ex: cytochrome)

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12
Q

What is apoenzyme and holoenzyme?

A

A catalytically active enzyme-cofactor complex is called holoenzyme.

The enzymatically inactive protein resulting from the removal of a holoenzyme’s cofactor is referred to as an apoenzyme.

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13
Q
  • Describe transition state theory, ΔGand ΔG
A

■ ΔG - overall free energy change for a reaction, related to the equilibrium constant

■ ΔG‡ - free energy of activation for a reaction, related to the rate constant

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14
Q
  • Given a free energy diagram of a reaction be able to determine the rate limiting step
A

The highest curve on graph

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15
Q
  • Define ΔΔGcat and be able to calculate rate enhancement
A

Enzymes provide an alternative pathway for the reaction to occur that has a lower ΔGǂ

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16
Q

What is Acid-base catalysis? What is the mechanism?

A

■ Most enzymes are active in a narrow pH range

– Substrate binding

– Ionization state of amino acids

– Ionization state of substrate

– Variation in protein structure

May use acid and base catalysis simultaneously

■ RNAse A

■ His 12 – general base

■ His 119 – general acid

■ Second step

■ His 12 – general acid

■ His 119 – general base

17
Q

What is Covalent catalysis? What is the mechanism?

A

Forms transient enzyme-substrate covalent bond

■ Primary amine attacks carbonyl forming Schiff base

Forms transient enzyme-substrate covalent bond

Nucleophiles

  • Hydroxyl Group
  • Sulfhydryl Group
  • Amino Group
  • Imidazole Group
18
Q

What is Metal Ion (Metalloenzyme) catalysis? What is the mechanism?

A

Substrate orientation

■ Red-Ox reactions – can alter metal oxidation state

■ Electrostatically shielding or stabilizing negative charges

■ Carbonic Anhydrase

■ Zn2+ polarized a water molecule to form OH- which acts as a nucleophile to attack CO2

19
Q

What is the Proximity and Orientation Effect? What is the mechanism?

A

■ Bring substrates together

By binding to their substrates enzymes:

– Facilitate proper orientation

– Electrostatic catalysis

– charged groups stabilize transition state – Limit relative movement of substrate

20
Q

What is Transition state binding? What is the mechanism?

A

■ Enzyme may preferentially bind the transition state over the undistorted substrate

■ Drugs that resemble the transition state may inhibit the enzyme