$$\text{Fraction ionized} = \frac{1}{1 + 10$$^{(pK_a - pH)}$$}$$

Question 1

Which of the following best describes the region where the average net charge of glycine is zero?

Accepted Answer

The pH is equal to the isoelectric point ($$pI) of $$glycine.

Question 2

At which pH does the carboxyl group of glycine become 50% ionized?

Accepted Answer

At the pH equal to the pK$$_a of $$the carboxyl group.

Question 3

Which formula is used to calculate the isoelectric point ($$pI) of $$glycine?

Accepted Answer

$$pI = \frac{pK_{a,1} + pK_{a,2}}{2}$$

Question 4

If the pK$$_a of $$glycine's carboxyl group is 2.3 and the pK$$_a of $$its amino group is 9.6, what is the isoelectric point ($$pI$$)?

Accepted Answer

$$pI = \frac{2.3 + 9.6}{2} = 5.95$$

Question 5

A solution of glycine at pH 1.0 will have which predominant ionic form?

Accepted Answer

Both amino and carboxyl groups are protonated.

Question 6

At a pH above 9.6, what is the net charge of glycine?

Accepted Answer

Net charge is -1.

Question 7

Which region on a titration curve of glycine corresponds to the pK$$_a of $$the amino group?

Accepted Answer

The second buffer region at high pH.

Question 8

During the titration of glycine, which equation can be used to estimate the fraction of ionized amino groups at a given pH?

Accepted Answer

$$	ext{Fraction ionized} = \frac{1}{1 + 10$$^{(pK_a - pH)}$$}$$

Question 9

A patient’s blood pH drops to 7.0. Considering the pK$$_a$$ values of glycine, which ionic form will predominate?

Accepted Answer

Glycine will be mostly in its zwitterionic form.

Question 10

Which of the following best explains why glycine acts as a buffer near its pK$$_a$$ values?

Accepted Answer

It can donate or accept protons, minimizing pH changes.

Question 11

If you add a strong acid to a glycine solution at its isoelectric point, what will happen to the net charge of glycine?

Accepted Answer

The net charge will become positive.

Question 12

Which of the following is true about the titration curve of glycine?

Accepted Answer

It has two buffer regions corresponding to the pK$$_a$$ values of the carboxyl and amino groups.

Question 13

A biochemist wants to prepare a buffer at pH 2.3 using glycine. Which group will be most effective in buffering at this pH?

Accepted Answer

The carboxyl group.

Question 14

Which statement best describes the state of glycine at pH 12?

Accepted Answer

Both carboxyl and amino groups are deprotonated.

Question 15

Which equation would you use to determine the net charge of glycine at a given pH?

Accepted Answer

$$	ext{Net charge} = (+1) 	imes 	ext{fraction protonated amino} + (-1) 	imes 	ext{fraction deprotonated carboxyl}$$

Question 16

During protein purification, why is it important to know the isoelectric point ($$pI) of $$amino acids like glycine?

Accepted Answer

Proteins are least soluble at their $$pI$$, aiding precipitation.

Question 17

If a solution contains glycine at pH 5.95, what is the predominant form?

Accepted Answer

Zwitterion (net charge 0)

Question 18

Which of the following best describes the effect of increasing pH on glycine’s structure?

Accepted Answer

The amino group loses a proton, increasing the negative charge.

Question 19

A researcher titrates glycine and observes two inflection points. What do these points represent?

Accepted Answer

The pK$$_a$$ values of the carboxyl and amino groups.

Question 20

Which of the following is a correct application of the Henderson-Hasselbalch equation for glycine’s carboxyl group?

Accepted Answer

$$pH = pK_a + \log \left( \frac{[A^-]}{[HA]} \right)$$

Amino Acid Ionization and Titration: Glycine as a Model

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