$$\text{pH} = \text{pKa} + \log \frac{[A^-]}{[HA]}$$

Zwitterionic form ($$\text{H}_3\text{N}^+-\text{CH}_2-\text{COO}^-)$$

The carboxylate group ($$\text{COO}^-) $$will capture a proton and become $$\text{COOH}$$

Question 1

Which equation represents the relationship between pH, pKa, and the ratio of conjugate base to acid in a buffer system?

Accepted Answer

$$	ext{pH} = 	ext{pKa} + \log \frac{[A^-]}{[HA]}$$

Question 2

A solution contains equal concentrations of $$	ext{HA}$$ and $$	ext{A}^-. $$What is the pH relative to the pKa?

Accepted Answer

pH is equal to pKa

Question 3

Which of the following best describes the buffering region of a polyprotic acid, as shown in the titration curve for $$	ext{H}_3	ext{PO}_4$$?

Accepted Answer

Buffering occurs at each pKa value

Question 4

Which form of glycine predominates at a pH of 7.0, based on its titration curve?

Accepted Answer

Zwitterionic form ($$	ext{H}_3	ext{N}^+-	ext{CH}_2-	ext{COO}^-)$$

Question 5

What is the effect of adding a strong acid to a solution containing amino acids in their zwitterionic form?

Accepted Answer

The carboxylate group ($$	ext{COO}^-) $$will capture a proton and become $$	ext{COOH}$$

Question 6

Which of the following statements about the peptide bond is correct?

Accepted Answer

The peptide bond has partial double bond character, restricting rotation

Question 7

In the context of protein structure, what is the primary stabilizing force for alpha helices?

Accepted Answer

Hydrogen bonds between the NH and CO groups of the main chain

Question 8

Which amino acid is most likely to be found at every third position in the collagen triple helix, and why?

Accepted Answer

Glycine, because it is small enough to fit in the interior of the helix

Question 9

What is the role of vitamin C in collagen synthesis?

Accepted Answer

It acts as a cofactor for prolyl hydroxylase, enabling hydroxylation of proline residues

Question 10

Which of the following best explains why hemoglobin exhibits a sigmoidal oxygen-binding curve, while myoglobin does not?

Accepted Answer

Hemoglobin binds oxygen cooperatively, while myoglobin binds oxygen independently

Question 11

What is the effect of 2,3-bisphosphoglycerate (2,3-BPG) on hemoglobin's oxygen affinity?

Accepted Answer

2,3-BPG decreases hemoglobin's oxygen affinity by stabilizing the T state

Question 12

In sickle cell disease, which amino acid substitution leads to hemoglobin aggregation in the deoxy form?

Accepted Answer

Glutamate is replaced by valine at position 6 of the beta chain

Question 13

Which of the following best describes the Bohr effect in hemoglobin?

Accepted Answer

Decreased pH leads to decreased oxygen affinity, promoting oxygen release in tissues

Question 14

Which of the following is true regarding the formation of salt bridges in hemoglobin at low pH?

Accepted Answer

Salt bridges stabilize the T state, favoring oxygen release

Question 15

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

Accepted Answer

The curve shows two distinct buffering regions corresponding to the pKa values of the amino and carboxyl groups

Question 16

Which of the following best describes the effect of hyperventilation on blood pH?

Accepted Answer

Hyperventilation decreases CO$$_2$$ concentration, shifting equilibrium left and increasing blood pH

Question 17

Which of the following is a consequence of the partial double bond character of the peptide bond?

Accepted Answer

No rotation is allowed around the peptide bond

Question 18

Which of the following best explains why buffers are most effective at a pH near their pKa?

Accepted Answer

At pH near pKa, the concentrations of acid and conjugate base are nearly equal, maximizing resistance to pH changes

Biochemistry Study Notes: Acid-Base Chemistry, Buffers, Amino Acids, Protein Structure, and Hemoglobin

Study Guide - Practice Questions