Question

Hemoglobin and myoglobin both have, are, can, or do all of the following except A. subunits that provide hydrogen bonds to and nonpolar interaction with other subunits. B. highly \(\alpha\) helical. C. bind one molecule of heme per globin chain. D. bind heme in a hydrophobic pocket. E. bind one \(\mathrm{O}_{2}\) per heme.

Short answer

A. Subunits that provide hydrogen bonds to and nonpolar interaction with other subunits. B. Highly α helical. C. Bind one molecule of heme per globin chain. D. Bind heme in a hydrophobic pocket. E. Bind one \(\mathrm{O}_{2}\) per heme. Answer: A. Subunits that provide hydrogen bonds to and nonpolar interaction with other subunits.

Step-by-step solution

Option A

Subunits that provide hydrogen bonds to and nonpolar interaction with other subunits: Hemoglobin is a tetramer composed of four polypeptide chains, two alpha and two beta chains. These subunits have hydrogen bonds and nonpolar interactions between them. On the other hand, myoglobin is a monomer and doesn't have subunits to interact like hemoglobin does. Therefore, this property is not common between them.

Option B

Highly \(\alpha\) helical: Both hemoglobin and myoglobin have a highly \(\alpha\) helical structure. These α-helices provide stability to the protein. So, this property is common between them.

Option C

Bind one molecule of heme per globin chain: Both hemoglobin and myoglobin contain a heme group, which is responsible for binding to oxygen. Each globin chain in hemoglobin or myoglobin binds one molecule of heme. So, this property is common between them.

Option D

Bind heme in a hydrophobic pocket: Both hemoglobin and myoglobin bind the heme group in a hydrophobic pocket, protecting it from oxidation due to their hydrophobic amino acids. So, this property is common between them.

Option E

Bind one \(\mathrm{O}_{2}\) per heme: Both hemoglobin and myoglobin bind to a single \(\mathrm{O}_{2}\) molecule per heme group. So, this property is also common between them. Based on the analysis above, we conclude that the correct answer is: A. Subunits that provide hydrogen bonds to and nonpolar interaction with other subunits.

Key concepts

Protein Structure

Proteins are fundamental components of living organisms and play a critical role in nearly all biological processes. The structure of proteins is organized into four levels: primary, secondary, tertiary, and quaternary.

The primary structure refers to the linear sequence of amino acids in the polypeptide chain. This sequence determines how the protein will fold and ultimately what function it will perform. Secondary structures are repetitive patterns within sections of a polypeptide chain, commonly taking the form of \( \alpha \) helices and \( \beta \) sheets. These structures are stabilized by hydrogen bonds between the backbone atoms in the polypeptide chain.

When discussing hemoglobin and myoglobin in the context of protein structure, we are particularly focused on the \( \alpha \) helical content. These helices contribute to the stability and flexibility required for their function in oxygen transport. Hemoglobin, which is composed of four subunits, demonstrates quaternary structure, while myoglobin with its single polypeptide chain, exemplifies tertiary structure.

Understanding the structural complexity of these proteins is crucial for appreciating how they carry out their roles in the body. The dynamic nature of their folding and interactions with other molecules showcases the intricate design of biological systems.

Heme Group Binding

The heme group is a vital component for many proteins, including hemoglobin and myoglobin, due to its ability to bind and transport oxygen. This prosthetic group contains an iron atom at its center, which is where oxygen binding takes place.

In these proteins, the heme is nestled within a hydrophobic pocket. This specific environment is nonpolar, meaning it repels water and other polar compounds, which protects the iron from oxidation and allows it to bind oxygen more effectively. A single heme group is bound to each polypeptide chain in hemoglobin and myoglobin, allowing for oxygen transport.

The hydrophobic pocket's construction involves various amino acids that create a nonpolar environment and hold the heme securely in place through interactions with the iron atom. This specialized binding site is an excellent example of how protein structure is intricately linked to function, and it emphasizes the accuracy of biological systems to perform vital tasks like oxygen transport.

Oxygen Transport in Blood

Oxygen transport in the blood is an essential life process, and hemoglobin and myoglobin play pivotal roles in this biological function. Both proteins are equipped to transport oxygen, but they do so under different circumstances and with varying efficiencies.

Hemoglobin is mainly found in red blood cells and is responsible for transporting oxygen from the lungs to the rest of the body. Its four subunits allow it to bind up to four oxygen molecules at once. An interesting characteristic of hemoglobin is its cooperative binding: the binding of one oxygen molecule increases the affinity for the next one, a phenomenon known as 'cooperativity.' This allows for efficient oxygen uptake in the lungs and delivery to tissues where oxygen concentration is low.

Myoglobin, in contrast, serves as an oxygen storage unit and has a higher affinity for oxygen than hemoglobin. Located in muscle tissue, it grabs oxygen from hemoglobin and stores it until it's needed during periods of intense muscular activity. Its structure, with a single heme group, allows it to hold onto oxygen even at lower concentrations, ensuring that muscles receive sufficient oxygen to meet their metabolic needs.

The intricacies of oxygen transport reflect the fine-tuning of physiological systems and highlight the importance of understanding proteins like hemoglobin and myoglobin, which are central to the basic functions of life.