6.5 Enzymes and the Rate of Chemical Reactions

Allosteric Enzymes

an enzyme whose activity is affected by binding a molecule at a site other than the active site. typically, allosteric enzymes change their shape on binding an activator or inhibitor.

If you added an enzyme that catalyzes the reaction shown, you would predict that ___ would be reduced but ___ would remain the same. A) arrow b; arrow e B) arrow d; arrow e C) arrow e; arrow b D) arrow e; arrow c E) arrow b; arrow c

A) arrow b; arrow e

How does protein folding allow for enzyme specificity?

An enzyme will only act on those substrates that bind to its active site (the portion of the enzyme that binds substrate and converts it to product). An enzyme has to fold into its correct shape for the active site to be the right shape to bind its substrate.

In a reaction, enzymes change the: A) second law of thermodynamics B) activation energy C) types of products D) first law of thermodynamics E) ΔG

B) activation energy

You notice that a chemical reaction in your system is happening at a slow rate. You want to speed up the reaction. What do you do? A) increase the activation energy B) add an enzyme that catalyzes the reaction C) change the ΔG for the reaction D) add more products

B) add an enzyme that catalyzes the reaction

Which labeled arrow in the figure represents the activation energy (Ea)? A) arrow A B) arrow B C) arrow C D) arrow D E) arrow E

B) arrow B

In this figure, the solid blue curve plots free energy of a reaction against progress of that reaction. This reaction is: A) exergonic B) endergonic C) more info is needed in order to answer the question

B) endergonic

The highest free energy is found in the _____(s) of a reaction. A) starting substrate B) transition state C) end product

B) transition state

What are the functions of an enzyme? Choose all that apply. A) to allow a reaction to be reversible B) to alter the equilibrium of a specific reaction C) to lower the activation energy for the reaction D) to increase the rate of a specific reaction E) to alter the ΔG of a specific reaction

C) to lower the activation energy for the reaction D) to increase the rate of a specific reaction

Which of the statements is true of allosteric inhibitors of an enzyme? A) allosteric inhibitors are structurally similar to the normal substrate of an enzyme B) allosteric inhibitors increase the rate of enzyme activity C) allosteric inhibitors bind to the active site of the enzyme D) allosteric inhibitors decrease enzyme activity

D) allosteric inhibitors decrease enzyme activity

The transition state is that portion of the process of a chemical reaction with a large amount of energy found in ____ reactions. A) endergonic B) exergonic C) non-spontaneous D) both endergonic and exergonic

D) both endergonic and exergonic

Which labeled arrow in the figure represents the change in free energy of the reaction (ΔG)? A) arrow A B) arrow B C) arrow C D) arrow D E) arrow E

E) arrow E

Which of the following do enzymes change? ΔG, reaction rate, types of product, activation energy, the laws of thermodynamics.

Enzymes increase the reaction rate and decrease the activation energy. Enzymes do not change the other parameters.

What are three characteristics of enzymes, and how does each permit chemical reactions to occur in cells?

Enzymes reduce the activation energy of a chemical reaction (or the energy input necessary to reach the transition state) by stabilizing the transition state and decreasing its free energy. Enzymes are catalysts that participate in a chemical reaction, forming complexes with products and reactants, but are not themselves consumed in the process. Enzymes are also highly specific. They typically catalyze only one reaction, recognizing a specific substrate. Finally, inhibitors and activators can influence enzyme activity. Inhibitors decrease the activity of enzymes, whereas activators increase this activity.

Activators

a compound that increases the activity of an enzyme

Substrate

a molecule acted upon by an enzyme (usually the reactant)

Enzyme

a protein that functions as a catalyst to accelerate the rate of a chemical reaction; enzymes are critical in determining which chemical reactions take place in a cell.

Inhibitors

a synthesized compound that decreases the activity of an enzyme

Transition State

the brief time in a chemical reaction in which chemical bonds in the reactants are broken and new bonds in the product are formed

Negative Feedback

the effect in which the final product of a biochemical pathway inhibits the first step; the process in which a stimulus acts on a sensor that communicates with an effector, producing a response that opposes the initial stimulus. Negative feedback is used to maintain steady conditions, or homeostasis.

Activation Energy (Ea)

the energy input necessary to reach the transition state

Active Site

the portion of an enzyme that binds substrate and converts it to product