The flow of carbon metabolism has been discussed in details in the article Glucose oxidation: an unpacking of energy. Glucose generated in the process of photosynthesis by fixing atmospheric carbon dioxide finally releases the CO2 into the blood of animals. But what after that? Here, the pH of water at the cellular level makes the bigger difference. During glucose oxidation energy is extracted and released CO2 gets converted to HCO3- in the blood which leads to reduced local pH.
Change in pH of blood is associated with oxygen transport in blood
In the reduced pH condition haemoglobin looses its affinity towards oxygen due to the binding of H+ ions and CO2 resulting into the release of oxygen in the tissue for the consumption by cells. In the lungs, CO2 gets disassociated from haemoglobin raising the pH, which again increases the affinity of haemoglobin towards Oxygen for transport. This simple interplay between the pH and CO2 concentration assures the constant supply of oxygen to all the organs in the animal body.
On the other hand, some organisms live at the extreme environmental conditions which include the temperature differences, low pH. We have seen in the article pH of water and its biochemical consideration-I that a functional properties of the biomolecules are largely dependent on the surrounding environment. Depending upon the range of pH at which an enzyme or protein is functional, it is possible to predict the amino acids present at the binding site of the corresponding enzyme or protein.
pH and evolution of biomolecules
The ester linkages in the lipids of bacteria and eukaryotes are prone to hydrolysis in the acidic environment. In order to survive the extremely low pH condition archaea have evolved with more stable ether bonds instead of ester bonds to survive in the low pH and high-temperature conditions. Depending upon their survival strategies organisms are classified as acidophiles and alkalophiles
Application of pH in daily life
In the article pH of water and its biochemical consideration-I we have also seen that protein structures are prone to changing pH of the solution. When subjected to the extreme alkaline or acidic pH, protein molecules undergo denaturation and often precipitate. Which is why since ancient time some foods are purposefully stored at low pH environment to restrict the growth of the microbes and increase the shelf life of the foods. Lactose from milk is a favourite food of Lactobacillus bulgaricus bacterium and it ferments lactose to produce lactic acid dropping the pH of milk. This drop in pH precipitate the casein protein from milk forming one of the beloved food of the world, called as yogurt.
Alteration in changes in normal pH levels of body fluids have significant impact on the physiological balance. Acidosis is a major outcome of one of the diabetic condition in which use of fatty acids over the glucose, mediate increased accumulation of certain acids in the blood lowering the pH. This lowering pH manifests multiple conditions which if left untreated can lead to extreme medical conditions. This specific medical condition is known as acidosis and monitored by routine inspection of the pH.
Apart from all of these phenomenon, a net difference in the pH values plays a vital role in capturing a light energy through a process of photosynthesis. Also the gradient of the hydrogen ions across the membrane creates energy difference which then used for the synthesis of the energy currency called as ATP.
Constantly changing pH of the water and other biological fluids pose a big challenge in maintaining the healthy and constant growth habit of an individual. With the evolution of millions of years most of the surviving life forms have adapted a peculiar mechanisms to mitigate the serious consequences occurring due to change in pH. It is especial challenging when metabolism involves many acidic metabolic intermediates giving off large number of ionic hydrogen. That is why, a very intricate regulation of all the metabolic pathway have been evolved.
