Question

Adult human haemolgobin consists of (a) 2 subunits \((\alpha, \alpha)\) (b) 2 subunits \((\beta, \beta)\) (c) 4 subunits \((2 \alpha, 2 \beta)\) (d) 3 subunits \((2 \alpha, 1 \beta)\).

Short answer

Adult human hemoglobin consists of 4 subunits (2 \(\alpha\), 2 \(\beta\)).

Step-by-step solution

Understanding Hemoglobin Structure

Hemoglobin is a protein found in red blood cells that is responsible for carrying oxygen from the lungs to the rest of the body. Its structure is made up of subunits that bind oxygen.

Identifying the Subunits

Adult human hemoglobin, also known as Hemoglobin A, is comprised of four polypeptide chains. Specifically, it has two types of chains named alpha (α) and beta (β).

Determining the Combination of Subunits

Each hemoglobin molecule is made up of two alpha (α) chains and two beta (β) chains. These combine to form a complete hemoglobin protein.

Key concepts

Hemoglobin Subunits

Hemoglobin is one of the most vital proteins in the human body as it is essential for the transport of oxygen from the lungs to tissues and the return of carbon dioxide back to the lungs for expulsion. The structure of this critical protein includes multiple subunits. Each hemoglobin molecule is comprised of four subunits, arranged into a pair of identical protein chains. Based on its structural composition, the correct answer to the exercise is (c) 4 subunits
(
2
alpha, 2
beta). These subunits work in tandem and are often referred to as globins. Adult human hemoglobin, denoted as Hemoglobin A, consists of two alpha (
α) chains and two beta (
β) chains. Each of these chains holds a heme group – an iron-containing compound that can bind to one molecule of oxygen, allowing hemoglobin to carry out its life-sustaining function of oxygen transport. This sophisticated arrangement not only facilitates the binding of oxygen molecules but also induces conformational changes that enhance the protein's ability to pick up and release oxygen at proper rates depending on the physiological conditions, such as the oxygen concentration in different parts of the body.

Oxygen transport

Oxygen transport is the most well-known function of hemoglobin. The process of transporting oxygen throughout the body begins when oxygen molecules enter the blood via the lungs. These molecules encounter hemoglobin within the red blood cells and bind reversibly to the iron atoms in the heme groups. Each hemoglobin molecule can bind up to four oxygen molecules, one per subunit, corresponding to the four heme groups it possesses.
As blood circulates and reaches areas with lower oxygen concentration, hemoglobin releases the oxygen molecules, which then diffuse into the surrounding tissues to maintain cellular functionality. The affinity of hemoglobin for oxygen is regulated by various factors, including pH levels, carbon dioxide concentration, and the presence of 2,3-bisphosphoglycerate (2,3-BPG). Superbly adapted to its role, hemoglobin's structure allows it to efficiently pick up oxygen in the high-oxygen environment of the lungs and release it in the low-oxygen environment of the tissues – a perfect example of structure complementing function.

Polypeptide Chains

Diving deeper into hemoglobin's polypeptide chains provides further insight into its functional versatility. Polypeptide chains, the building blocks of proteins, are long sequences of amino acids bound together by peptide bonds. The sequence of amino acids in each chain determines its unique three-dimensional structure and function.
In hemoglobin, the alpha (
α) and beta (
β) chains are different polypeptides with their own specific sequences, which allow them to fold and function together as a unit. The folding of these chains is crucial for the stability of hemoglobin and its capacity to transport oxygen. Mutations or alterations in the amino acid sequences of these chains can lead to variations in hemoglobin function, some of which are associated with diseases such as sickle cell anemia and thalassemia. Thus, the precise arrangement of amino acids in these polypeptide chains is critical for the proper operation of hemoglobin in oxygen transport.