Day 74 MCAT Practice Question

Passage 4: Hemoglobin

Hemoglobin is a vital protein found in red blood cells that is responsible for

transporting oxygen from the lungs to tissues throughout the body. The

structure of hemoglobin is crucial to its function and is a prime example of the

relationship between protein structure and function.



Hemoglobin is a tetramer composed of four subunits: two α-globin and two β globin

chains. Each subunit contains a heme group, which consists of an iron atom bound

to a porphyrin ring. The iron atom in the heme group is responsible for reversibly

binding to oxygen molecules. The globin chains fold into a globular shape, creating a

hydrophobic pocket that protects the heme group and facilitates oxygen binding

The conformational stability of hemoglobin is maintained by various intramolecular

interactions. These interactions allow hemoglobin to maintain its tertiary and

quaternary structure, which is essential for its function. However, certain conditions,

such as changes in pH or the presence of allosteric effectors, can alter the

conformational stability of hemoglobin and affect its oxygen-binding properties.

Hemoglobin exhibits cooperative binding, which is achieved through allosteric

interactions between the subunits. When one subunit binds to oxygen, it induces

a conformational change in the other subunits, making them more receptive to

oxygen binding. This property allows hemoglobin to efficiently load oxygen in the

lungs and release it in the tissues.



The oxygen-binding affinity of hemoglobin can be modulated by various

factors, such as pH, carbon dioxide concentration, and the presence of 2,3-

bisphosphoglycerate (2,3-BPG).



Hemoglobin can be separated and purified using various techniques, such

as ion-exchange chromatography and gel filtration. These techniques rely

on the differences in charge and size of the protein molecules. Ion-exchange

chromatography separates proteins based on their net charge, while gel filtration

separates them based on their molecular size and shape.

Cooperative binding in hemoglobin refers to:

A) The binding of oxygen to the iron atom in the heme group

B) The binding of oxygen to the globin chains

C) The increased affinity for oxygen in the remaining subunits when one

subunit binds oxygen

D) The decreased affinity for oxygen in the remaining subunits when one

subunit binds oxygen