3. Enzyme Kinetics

Question 1

What effects do enzymes have?

Answer 1

The free energy change (deltaG) of the catalyzed rxn is the same as for the uncatalyzed rxn; enzymes catalyze rxns by lowering their activation energy, and are not changed or consumed during the course of the rxn. While activation energy is lowered, the free energy of the rxn, deltaG, remains unchanged in the presence of an enzyme. A rxn will continue to occur in presence or absence of an enzyme

Question 2

Optimal conditions for enzyme activity

Answer 2

• temperature of 37 degrees C - pH of 7.4 (which is pH of most body fluids)

Question 3

Michaelis-Menten equation

Answer 3

enzymes form Enzyme-Substrate complex, which can either dissociate back into the enzyme and substrate or proceed to form a product

Question 4

At what point does an increase in [substrate] not increase rate of the rxn?

Answer 4

When the enzymes are totally saturated, then adding more substrate will have no effect on rxn rate

Question 5

Apoenzyme

Answer 5

an enzyme DEVOID of the prosthetic group, coenzyme, or cofactor necessary for normal activity

Question 6

Holoenzyme

Answer 6

an enzyme that has ALREADY BOUND a required prosthetic group, coenzyme, or cofactor

Question 7

Coenzyme

Answer 7

an organic molecule that helps an enzyme carry out its function

Question 8

Zymoenzyme/Zymogen

Answer 8

an enzyme that is secreted in the inactive form and must be activated by cleavage; common examples are digestive enzymes

Question 9

What factor determines an enzyme’s specificity?

Answer 9

Determined by the 3D shape of its active site; it determines which substrates the enzyme will react w/

Question 10

Finding Km of a graph or table

Answer 10

Km is [substrate] @ 1/2 vmax

Question 11

Lyase

Answer 11

responsible for breakdown of single molecule into 2 molecules w/o the addition of water or the transfer of electrons; lyases often form cyclic compounds or double bonds in the products to accomodate this

Question 12

What are some methods by which enzymes decrease activation energy for biological rxns?

Answer 12

1. Modifying the local charge environment
2. Forming transient covalent bonds
3. Acting as electron donor or receptors

HOWEVER, an enzyme is NEVER altered by the process of catalysis; a molecule that breaks intramolecular bonds to provide activation energy would not be able to be reused, so breaking bonds would not be a possible method

Question 13

Cooperative binding enzymes