The Bohr shift refers to the phenomenon where electrons in atoms emit or absorb photons of specific wavelengths when transitioning between quantized energy levels. According to Bohr's model, electrons can only exist in discrete energy states, often referred to as energy levels or orbits. When an electron transitions from a higher energy level to a lower energy level, it releases energy in the form of a photon. The energy of this photon is equal to the difference in energy between the two levels. This released energy corresponds to a specific wavelength of light. Conversely, when an electron absorbs a photon with energy equal to the energy difference between two levels, it can transition to a higher energy level. The emitted or absorbed photons have characteristic wavelengths, forming spectral lines. The Bohr shift is directly related to the quantized nature of energy levels within the atom. The specific wavelengths emitted or absorbed are determined by the particular atom and the energy level transitions involved.

The structure of haemoglobin is exquisitely adapted to facilitate efficient oxygen and carbon dioxide transport. Its functionality is directly linked to the interplay of its constituent components: the heme group, the iron ion, and the globin protein chains.

The heme group is the core functional unit of haemoglobin. It consists of a porphyrin ring, a complex organic molecule, with a central iron ion (Fe²⁺). The iron ion is crucial because it is the site where oxygen binds. The porphyrin ring stabilizes the iron ion and facilitates the reversible binding of oxygen. The four heme groups within each haemoglobin molecule allow for the binding of four oxygen molecules, contributing to haemoglobin's high oxygen-carrying capacity.

The globin protein chains are composed of four polypeptide chains (two alpha and two beta chains in adult haemoglobin). These chains provide a scaffold for the heme groups and contribute to the overall structure and stability of the haemoglobin molecule. The globin chains are responsible for the cooperative binding of oxygen. This cooperativity arises because the binding of one oxygen molecule to a heme group induces a conformational change in the globin chain, making it easier for subsequent oxygen molecules to bind. This results in a sigmoidal oxygen-binding curve, which is advantageous for efficient oxygen uptake in the lungs and release in the tissues.

The specific arrangement of the globin chains also allows for the binding of carbon dioxide. While CO₂ does not bind directly to the iron ion, it can bind to the globin chains, particularly to amino groups that have been protonated in acidic conditions. This binding of CO₂ helps to facilitate the release of oxygen in tissues with high CO₂ concentrations (the Bohr effect). The structure of haemoglobin, therefore, is a perfect example of form following function, with each component contributing to its overall efficiency in respiratory gas transport.

Carbonic anhydrase is an enzyme found in high concentrations within red blood cells. Its primary role is to catalyze the reversible reaction between carbon dioxide (CO2) and water (H2O) to form carbonic acid (H2CO3). This is a crucial step in the transport of CO2 because it allows for the conversion of CO2 into bicarbonate ions (HCO3-), which is the major form of CO2 transport in the blood.

The reaction equation is as follows:

In the tissues, where CO2 concentration is high, the enzyme facilitates the formation of carbonic acid, which then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). The bicarbonate ions are transported out of the red blood cells into the plasma, while the hydrogen ions bind to haemoglobin, contributing to the Bohr effect (which promotes CO2 release in the tissues).

In the lungs, the process is reversed. The enzyme catalyzes the breakdown of bicarbonate ions back into CO2 and water, which then diffuses into the alveoli to be exhaled.