Unit 3: Thermodynamics and Catalysts

Question 1

What does a negative free energy difference represent?

Answer 1

exergonic reaction - which will occur spontaneously as it releases energy

Question 2

What does a positive free energy difference represent?

Answer 2

endergonic reaction - will need to be paired with an exergonic reaction as this reaction requires energy and will never occur on its own

Question 3

From the point of view of the molecules involved, which of the following reactions illustrate an increase in entropy?

a) condensation
b) hydrolysis
c) polymerization
d) formation of glycosidic bonds
e) formation of phosphodiester bonds

Answer 3

b) hydrolysis - CORRECT

Everything else would require the addition of energy for the reaction to proceed making it a decrease in entropy

Question 4

Which of the following is not true when comparing an un-catalyzed reaction to the same reaction with a catalyst?

a) the catalyzed reaction will be faster
b) the catalyzed reaction will release a different amount of free energy
c) the catalyzed reaction will have lower activation energy
d) the catalyzed reaction will not consume any of the catalyst

Answer 4

b) the amount of free energy will always be the same rather a catalyst was used or not, the amount of energy required at the beginning of the reaction will be different though

Question 5

Activation energy…

a) refers to the energy stored in chemical bonds
b) is reduced by enzyme catalysts
c) refers to the energy associated with the thermal motion of atoms and molecules within a living cell
d) refers to the fact that energy cannot be created or destroyed
e) is maximized by enzyme catalysts

Answer 5

b) reduced by enzyme catalysts

Question 6

A reaction with a large positive free energy difference will….

a) be spontaneous
b) highly endergonic
c) proceed more rapidly than a reaction with a small positive free energy difference
d) proceed when coupled to another reaction with a small negative free energy difference
e) a and c

Answer 6

b) highly endergonic

Question 7

Which of the following is true as it relates to the phosphorylation of enzymes

a) phosphorylation of enzymes always increases its activity
b) phosphorylation of an enzyme always decreases its activity
c) phosphates can be added to R groups of any amino acid
d) phosphate groups are added by a class of enzymes known as kinases

Answer 7

d) added through kinase enzymes and removed through phosphatase enzymes

Question 8

Enzyme in HIV called protease was discovered. Once the enzyme’s structure was known, researchers began developing drugs that fit into the active site and blocked it. This strategy for stopping HIV infections is an example of?

a) feedback regulation
b) immunization
c) allosteric regulation
d) competitive inhibition

Answer 8

d)

Question 9

Enzymes catalyze reactions by:

a) lowering the activation barrier for an exergonic reaction
b) changing the equilibrium of the reaction to favour product formation
c) decreasing the free energy difference between reactants and products
d) a and c
e) all of the above

Answer 9

a)

Question 10

Enzyme-catalyzed reactions increase in rate very rapidly at low substrate concentrations but plateau at higher substrate concentrations. Why?

a) As substrate concentrations increase, the concentrations of inhibitors increase in order to keep the enzyme under control
b) At high substrate concentrations, the active sites on the enzyme molecules are all occupied, and the enzymes are therefore working at maximal speed
c) hydrogen ions are produced as a side effect of enzyme-catalyzed reactions, and the increasing acidity inactivates the enzymes
d) an activator is necessary to maintain high reaction rates when substrate concentrations are high

Answer 10

b)