Chapter 8- Mechanisms and Inhibitors

Question 1

What are four strategies for catalyzing an enzyme might use? Explain briefly

Answer 1

1. Covalent Catalysis; active site contains reactive group that becomes modified during catalysis
2. General Acid-Base Catalysis; molecule plays the role of a proton donor or acceptor
3. Metal Ion Catalysis; Many metal ions are cofactors, They can bind to substrate increasing interactions with enzyme, or stabilize or add a charge
4. Catalysis by Approximation and Orientation; presence of two substrates and putting them in right orientation increases reaction rate

Question 2

What are environmental factors that affect enzyme acitivity?

Answer 2

Temperature, pH, inhibitory molecules

Question 3

What is the effect of temperature on the working of an enzyme?

Answer 3

A rise in temperature increases likelihood of interactions between enzyme and substrate. If temperature is too high, movement of polypeptide chains is so strong that protein loses 3d structure, denaturing

Question 4

What is the effect of pH changes on enzymes?

Answer 4

Enzymes have an optimal pH, at which it works properly with the right side-chains protonated or deprotonated. If the pH changes, side chains might become a different charge than optimal, making the enzyme inactive

Question 5

What are the three methods of reversible inhibition?

Answer 5

competitive, uncompetitive and noncompetitive inhibition

Question 6

How does competitive inhibition work? Can substrate bind or not at all?

Answer 6

The inhibitor binds to the active site of the enzyme, preventing substrate from doing so. It lowers the proportion of enzymes bound to a substrate, but the inhibition can be overcome by increasing the substrate concentration

Question 7

How does uncompetitive inhibition work?

Answer 7

Uncompetitive inhibition requires the enzyme-substrate complex to be made before binding. The binding site is only created when the ES complex is present.

Question 8

How does noncompetitive inhibition work?

Answer 8

the inhibitor and substrate bind to an enzyme at different sites, changing the conformation of the enzyme and thus not having an active enzyme-substrate complex.

Question 9

Explain how irreversible inhibition works

Answer 9

The inhibitor binds tightly to the enzyme, letting go only very slowly again.

Question 10

What are the four categories of irreversible inhibitors? Name their characteristics

Answer 10

1. Group-specific reagents; they modify specific R groups of amino acids
2. Substrate analogs or affinity labels; covalently modify the active-site residues, the inhibitor is similar to substrate
3. Suicide inhibitors; chemically modified substrates bind to the enzyme, generating an intermediate that inactivates the enzyme
4. Transition-state analogs; bind to the active site stronger than normal substrate, inhibiting the use of the enzyme.