ch3 part D

4. List five characteristics of enzymes.

1. An enzyme undergoes no net chemical change as a result of catalyzing a reaction. 2. The binding of substrate to an enzyme's active site has all the characteristics—chemical specificity, affinity, competition, and saturation—of a ligand binding to a protein. 3. An enzyme increases the rate of a chemical reaction but does not cause a reaction to occur that would not occur in its absence. 4. Some enzymes increase both the forward and reverse rates of a chemical reaction, and thus do not change the chemical equilibrium that is finally reached. They only increase the rate at which equilibrium is achieved. 5. An enzyme lowers the activation energy of a reaction but does not alter the net amount of energy that is added to or released by the reactants in the course of a reaction.

2. List the four factors that influence the rate of a chemical reaction and state whether increasing the factor will increase or decrease the rate of the reaction.

1. Reactant concentrations—increasing them increases the rate of reaction; 2. Activation energy—increasing it decreases the rate of reaction; 3. Temperature—increasing it increases the rate of reaction; 4. Catalysts—increasing them increases the rate of reaction.

5. What is the difference between a cofactor and a coenzyme?

A cofactor is a modulator molecule that binds to the regulatory site of allosteric enzymes. Cofactors are often trace metals. A coenzyme is an organic molecule that acts as a cofactor except that it participates in the reaction being catalyzed and accepts or donates a few atoms to the substrate. In a subsequent reaction, the atoms are returned to or taken away from the coenzyme so that it is restored to its original form.

1. How do molecules acquire the activation energy required for a chemical reaction?

Activation energy is acquired when reactants collide. Increasing the temperature increases the likelihood of reaching activation energy because it increases the speed of molecular movement and thus the energy of impact. Catalysts reduce the activation energy of a reaction.

9. How can an "irreversible step" in a metabolic pathway be reversed?

An "irreversible" step can be reversed if it is coupled to a reaction that releases large amounts of energy from the simultaneous breakdown of a molecule. A second enzyme that is different from the one that catalyzed the forward reaction is needed.

3. What characteristics of a chemical reaction make it reversible or irreversible?

If small quantities of energy are released by a chemical reaction and the product concentrations are only slightly higher than reactant concentrations at equilibrium, then the reaction is reversible. If large amounts of energy are released and almost all of the reactant molecules have been converted to product at equilibrium, then the reaction is irreversible.

7. Why are small concentrations of coenzymes sufficient to maintain enzyme activity?

Recycling of coenzymes back to their original form means that only a few coenzymes need to be present to catalyze many reactions.

6. From what class of nutrients are coenzymes derived?

Vitamins

8. List three ways to alter the rate of an enzyme

mediated reaction.- Altering substrate concentration, enzyme concentration, or enzyme activity