Day 13 MCAT Practice Question

Passage 2: Acid-Base Regulation

Understanding acid-base regulation is often reduced to pigeonholing clinical

states into categories of disorders based on arterial blood sampling. An earlier

ambition to quantitatively explain disorders by measuring the production and

elimination of acid has not become standard clinical practice. Seeking back to

classical physical chemistry, we propose that in any compartment, the requirement

of electroneutrality leads to a strong relationship between charged moieties.

Figure 1 shows the relationship between [H+] of a mixture and the mean [H+] of two

mixtures. Figure 2 shows the equations related to the water dissociation constant.

Strong Relationships in Acid-Base Chemistry – Modeling Protons Based on

Predictable Concentrations of Strong Ions, Total Weak Acid Concentrations, and

pCO2. Adapted from Ring & Kellum (2016).

Which of the following protein chemical characteristics is correctly associated

with its biological importance?

A) Ionic interactions between heme groups in hemoglobin; cooperative binding

of oxygen

B) Covalent bonding between actin monomers; polymerization of actin

C) Hydrogen bonding in collagen; tensile strength in connective tissues

D) Hydrophobic interactions in keratin; structural stability in hair and nails