Question 1

Which of the following best describes the isoelectric point ($pI$) of lysine, based on its titration curve?

Accepted Answer

The $pI$ is the average of the $pK_a$ values for the two groups that lose protons near neutral pH.

Question 2

Given the titration curve of lysine, at which region does the molecule act as the best buffer?

Accepted Answer

At pH values near each $pK_a$.

Question 3

Which equation correctly relates the Gibbs free energy change to enthalpy and entropy?

Accepted Answer

$\Delta G = \Delta H - T\Delta S$

Question 4

A spontaneous biochemical reaction must have which of the following properties?

Accepted Answer

A negative $\Delta G$

Question 5

Which statement best describes the hydrophobic effect in aqueous solutions?

Accepted Answer

Nonpolar molecules aggregate in an aqueous solution to decrease the amount of disordered water.

Question 6

At the midpoint of a titration curve for a weak acid, which of the following is true?

Accepted Answer

The concentrations of the weak acid $[HA]$ and the conjugate base $[A^-]$ are equal.

Question 7

Which of the following best describes diastereomers?

Accepted Answer

Non-mirror images of each other.

Question 8

If a solution of lysine is titrated and the pH is at the $pI$, what is the net charge on the molecule?

Accepted Answer

Zero

Question 9

During the titration of lysine, which functional group loses its proton first as pH increases?

Accepted Answer

The carboxyl group

Question 10

Which of the following is a correct statement about isomers?

Accepted Answer

Isomers have the same chemical formula but different arrangements of atoms.

Question 11

A buffer solution is most effective when:

Accepted Answer

The concentrations of acid and conjugate base are equal.

Question 12

Which of the following changes will increase the disorder (entropy) of the universe during a biochemical reaction?

Accepted Answer

Release of heat to the surroundings.

Question 13

If the $pK_a$ values for lysine are approximately 2.2, 9.0, and 10.5, what is the $pI$?

Accepted Answer

$pI = \frac{9.0 + 10.5}{2}$

Question 14

Which of the following is true about enantiomers?

Accepted Answer

They are mirror images of each other.

Question 15

A solution contains equal concentrations of a weak acid and its conjugate base. What is the pH of the solution relative to the $pK_a$?

Accepted Answer

pH $=$ $pK_a$

Question 16

Which of the following best explains why nonpolar molecules aggregate in water?

Accepted Answer

To maximize the entropy of water molecules.

Question 17

If a biochemical reaction absorbs energy and increases the disorder of the universe, what can be said about its spontaneity?

Accepted Answer

It may be spontaneous if $T\Delta S$ outweighs $\Delta H$.

Question 18

Which of the following is NOT a property of a good buffer?

Accepted Answer

It is composed of a strong acid and its conjugate base.

Question 19

Which of the following statements about the titration curve of lysine is correct?

Accepted Answer

There are three buffering regions, each corresponding to a $pK_a$ value.

Amino Acid Titration, Isomerism, Thermodynamics, and Buffer Systems in Biochemistry

Study Guide - Practice Questions