Applications of the Henderson-Hasselbalch equation

• Calculate the ratio of CB to WA, if pH is given

• Calculate the pH, if ratio of CB to WA is known

• Calculate the pH of a weak acid solution of known concentration

• Determine the pKa of a WA-CB pair

• Calculate change in pH when strong base is added to a solution of weak acid. This is represented in a titration curve

• Calculate the pI

The Hemoglobin Buffer Systems

These buffer systems are involved in buffering CO₂ inside erythrocytes. The buffering capacity of hemoglobin depends on its oxygenation and deoxygenation. Inside the erythrocytes, CO₂ combines with H₂O to form carbonic acid (H₂CO₃) under the action of carbonic anhydrase.

At the blood pH 7.4, H₂CO₃ dissociates into H⁺ and HCO₃ ⁻ and needs immediate buffering.

Acids and bases can be classified as proton donors and proton acceptors, respectively. This means that the conjugate base of a given acid will carry a net charge that is more negative than the corresponding acid. In biologically relavent compounds various weak acids and bases are encountered, e.g. the acidic and basic amino acids, nucleotides, phospholipids etc.

Weak acids and bases in solution do not fully dissociate and, therefore, there is an equilibrium between the acid and its conjugate base. This equilibrium can be calculated and is termed the equilibrium constant = K_a. This is also  referred to as the dissociation constant as it pertains to the dissociation of protons from acids and bases.

In the reaction of a weak acid:

HA <-----> A^- + H⁺

the equlibrium constant can be calculated from the following equation:

K_a = [H⁺][A^-]/[HA]

As in the case of the ion product:

pK_a = -logK_a

Therefore, in obtaining the -log of both sides of the equation describing the dissociation of a weak acid we arrive at the following equation:

-logK_a = -log[H⁺][A^-]/[HA]

Since as indicated above -logK_a = pK_a and taking into account the laws of logrithms:

pK_a = -log[H⁺] -log[A^-]/[HA]

pK_a = pH -log[A^-]/[HA]

From this equation it can be seen that the smaller the pK_a value the stronger is the acid. This is due to the fact that the stronger an acid the more readily it will give up H⁺ and, therefore, the value of [HA] in the above equation will be relatively small.

CALCIUM

Total calcium in the human body is 1 to 1.5kg, out of which 99% is seen in bone and 1% in extracellular fluid. The main source of calcium is milk.

The daily requirement of calcium for child is 1200mg/day and for adult it is 500mg/day. During pregnancy /lactation the calcium requirement is 1500mg/day.

The absorption of calcium takes place in 1st and 2nd part of deuodenum. Calcium absorption requires carrier protein, helped by Ca²⁺ - dependent ATpase.

Factors responsible for increase in calcium absorption include Vitamin D, Parathyroid hormone, acidity and amino acids. Factors such as phytic acid,oxalates, malabsorption  syndromes and Phosphates decreases calcium absorption. The normal calcium level in blood is 9-11mg/dl.

Cholesterol synthesis:

Hydroxymethylglutaryl-coenzyme A (HMG-CoA) is the precursor for cholesterol synthesis. 

HMG-CoA is also an intermediate on the pathway for synthesis of ketone bodies from acetyl-CoA. The enzymes for ketone body production are located in the mitochondrial matrix. HMG-CoA destined for cholesterol synthesis is made by equivalent, but different, enzymes in the cytosol.

HMG-CoA is formed by condensation of acetyl-CoA and acetoacetyl-CoA, catalyzed by HMG-CoA Synthase.

HMG-CoA Reductase, the rate-determining step on the pathway for synthesis of cholesterol.

BIOLOGICAL ROLES OF LIPID

Lipids have the common property of being relatively insoluble in water and soluble in nonpolar solvents such as ether and chloroform. They are important dietary constituents not only because of their high energy value but also because of the fat-soluble vitamins and the essential fatty acids contained in the fat of natural foods

Nonpolar lipids act as electrical insulators, allowing rapid propagation of depolarization waves along myelinated nerves

Combinations of lipid and protein (lipoproteins) are important cellular constituents, occurring both in the cell membrane and in the mitochondria, and serving also as the means of transporting lipids in the blood.