Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
26 Cards in this Set
- Front
- Back
|
How do enzymes change the rate of a reaction?
|
Lower the activation energy
|
|
|
T/F Enzymes shift the equilibrium of a rxn (change the Keq)
|
False, they do not
|
|
|
What are the 6 major classes of enzymes?
|
1. Oxidoreductases
2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases |
|
|
What are several ways in which enzymes accelerate the rate of the rxn they catalyze?
|
1. Stabilize the transition state
2. proximity effects 3. Microenvironment effects 4. Acid-base Catalysis 5. Covalent catalysis |
|
|
Are catalysts consumed in a rxn?
|
No
|
|
|
What is the most important way in which enzymes reduce the free energy of activation?
|
Stabilize the transition state
|
|
|
What's the difference between K eq and k r?
|
K eq = equilibrium constant, determined by the energy difference between A and B, unaffected by catalysts
k r = rate constant, determined by free energy of activation, reduced by catalysts |
|
|
If catalysts reduce the free energy of activation for A --> B, then the catalyst must also reduce the FE of activation for _________?
|
B --> A
|
|
|
Why does it make sense that metabolism reactions NOT occur without a catalyst?
|
If they occurred spontaneously, then there would be no way to control them
|
|
|
Distinguish kinetic control and thermodynamic control
|
A reaction can be thermodynamically favorable (products have lower free energy than reactants) but be kinetically UNfavorable (T* energy is too great). No reaction will occur without a catalyst
|
|
|
Why must the free energy of activation of A --> B NOT be too great in metabolism?
|
Because many reactions are reversible and if A-->B is too great, then B-->A will not be able to be catalyzed at 37C
|
|
|
What is an encounter complex?
|
When reactants diffuse together, water molecules cage them in, allowing for collisions to occur.
|
|
|
How many collisions can happen between A and B at room temperature before they diffuse apart?
|
150
|
|
|
When reactants collide, there must be two criteria met for them to react. What are the criteria?
|
1. Must collide with more energy than the energy of activation
2. Must collide with reactive groups in the correct orientation |
|
|
What are proximity effects?
|
By binding their substrates, enzymes increase the effective concentration of reactants within the active site.
|
|
|
Which amino acids have reactive side chains that can participate in enzyme catalysis?
|
Glu, Asp, Lys, Arg, Cys, His, Ser, Tyr
(8) |
|
|
What 2 general forms microenvironmental effects are observed with enzymes?
|
Hydrophobic and charge
|
|
|
What does desolvation mean?
|
when the solvent is removed from a solution
|
|
|
How does an enzyme provide a hydrophobic microenvironment and why is it important?
|
If the active site is lined with hydrophobic amino acids, then the functional groups become desolvated and more reactive. If the transition state is less polar than the products or substrates, it will be stabilized in the microenvironment.
|
|
|
How is the pKa of a Lys residue changed by another Lys residue?
|
The adjacent Lys, when protonated, makes it unfavorable for the active Lys to be protonated.
|
|
|
What does carboxypeptidase do?
|
Cleaves amino acids off the C terminus of proteins
|
|
|
What are the two steps of hydrolysis of a peptide bond?
|
1) Polarization of the peptide carboxyl group
2) Proximity of a nucleophile to attack the carbonyl atom. |
|
|
What's the difference between specific acid-base catalysis and general acid-base catalysis?
|
1) Specific = involves the constituents of water (H30+ and -OH)
2) General = Donor or acceptor are weak (as with many amino acid side chains) |
|
|
Which amino acid has a pH near physiological pH and can therefore act as an acid and base at the same time?
|
Histidine
|
|
|
In induced fit, how does the conformation change of the enzyme aid in catalysis?
|
The conformational change distorts the substrate into a more reactive state resembling the transition state.
|
|
|
What is covalent catalysis?
|
When a covalent enzyme-substrate intermediate is formed during the course of the reaction.
|
