Chapter 22

What is a pseudo-first-order reaction?

What is the difference between competitive inhibition and noncompetitive inhibition of an enzyme?

Why are heavy metals often poisons in the body?

What are coenzymes?

Suggest a way to test whether an enzyme inhibitor is competitive or noncompetitive.

Suggest how a Lineweaver-Burk plot can be used to determine whether an inhibitor is competitive or noncompetitive.

A first-order reaction requires 10.0 min for \(50 \%\) conversion to products. How much time is require for \(90 \%\) conversion? For \(99 \%\) conversion?

A first-order reaction required 25.0 s for \(30 \%\) conversion to products. What is the half-life of the reaction?

Sucrose is hydrolyzed to glucose and fructose: $$ \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} $$ In dilute aqueous solution, the water concentration remains essentially constant. and so the reaction is pseudo first order and follows first-order kinetics. If \(25.0 \%\) of a \(0.500 M\) sucrose solution is hydrolyzed in \(9.00 \mathrm{~h}\), in how much time will the glucose and fructose concentration be equal to one-half the concentration of the remaining sucrose?

Hydrogen peroxide decomposes by a second-order reaction, $$ 2 \mathrm{H}_{2} \mathrm{O}_{2} \stackrel{\text { catalyst }}{\longrightarrow} 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2} $$ If \(35.0 \%\) of a \(0.1000 M\) solution decomposes in \(8.60 \mathrm{~min}\), how much time is reauired for the evolution of \(100 \mathrm{~mL} \mathrm{O}_{2}\) from \(100.0 \mathrm{~mL}\) of a \(0.1000 \mathrm{M}\) solution of \(\mathrm{H}_{2} \mathrm{O}_{2}\) at standard temperature and pressure?

The activity of a glucose oxidase preparation is determined by measuring the volume of oxygen gas consumed as a function of time. A 10.0 -mg fraction of the preparation is added to a solution containing \(0.01 M\) glucose and saturated in oxygen. After 20.0 min, it is determined that 10.5 mL oxygen is consumed at standard temperature and pressure (STP). What is the activity of the enzyme preparation expressed in enzyme units per milligram? If the purified enzyme has an activity of 61.3 units/mg, what is the percent purity of this enzyme preparation?

When an apple is sliced, it turns brown on exposure to air due to catalysis of the oxidation of phenols in the apple by \(o\) -diphenyl oxidase enzyme. An experiment is performed to determine the Michaelis constant of \(o\) -diphenyl oxidase in which fresh pieces of apple are ground up and then centrifuged to produce a supernatant that will serve as the enzyme source (see www.ultranet. com/ -jkimball/BiologyPages/E/EnzymeKinetics.html). Catechol is used as the substrate. A fixed amount of the enzyme preparation is added to a tube containing \(0.300 \mathrm{mM}\) catechol, and the change in absorbance is measured at \(540 \mathrm{nm}\) at 1 -min intervals for several minutes. The experiment is repeated with three other tubes containing \(0.600,1.20,\) and \(4.80 \mathrm{mM}\) catechol. The following results are obtained \((\mathrm{m} M\) catechol/ \(\Delta A / \mathrm{min}): 0.30 / 0.020 ; 0.60 / 0.035\) \(1.20 / 0.048 ; 4.80 / 0.081 .\) Prepare a spreadsheet to determine \(K_{m}\)