Buffers           

• Biological systems use buffers to maintain pH.

• Definition: A buffer is a solution that resists a significant change in pH upon addition of an acid or a base.

• Chemically: A buffer is a mixture of a weak acid and its conjugate base

• Example: Bicarbonate buffer is a mixture of carbonic acid (the weak acid) and the bicarbonate ion (the conjugate base): H₂CO₃ + HCO₃ ^–

• All OH- or H+ ions added to a buffer are consumed and the overall [H+ ] or pH is not altered

H₂CO₃ + HCO₃ ^- + H⁺ <- -> 2H₂CO₃

H₂CO₃ + HCO₃ -  +  OH^-  <- -> 2HCO₃  ^- + H₂O

• For any weak acid / conjugate base pair, the buffering range is its pKa +1.

It should be noted that around the pK_a the pH of a solution does not change appreciably even when large amounts of acid or base are added. This phenomenon is known as buffering. In most biochemical studies it is important to perform experiments, that will consume H⁺ or OH^- equivalents, in a solution of a buffering agent that has a pK_a near the pH optimum for the experiment.

Most biologic fluids are buffered near neutrality. A buffer resist a pH change and consists of a conjugate acid/base pair.

Important Physiological Buffers include carbonate (H₂CO₃/HCO₃^-),

Phosphate (H₂PO^-₄ /HPO^2-₄) and various protiens

PHOSPHORUS

Serum level of phosphate is 3-4 mg/dl for adults and 5-6 mg/dl in children. Consumption of calcitriol increases phosphate absorption.

Functions of phosphorus
(a) Plays key role in formation of tooth and bone

(b) Production of high energy phosphate compounds such as ATP, CTP, GTP etc.,

(c) Synthesis of nucleotide co-enzymes such as NAD and NADP

(d) Formation of phosphodiester backbone structure for DNA and RNA synthesis

Hypophosphatemia is the condition which leads to decrease in absorption of phosphorus. it leads to hypercalcamia

Hyperphosphatemia, increase in absorption of phosphate was noticed. Hyperphosphatemia leads to cell lysis, hypocalcemia and thyrotoxicosis.

The Effects of Enzyme Inhibitors

Enzymes can be inhibited

• competitively, when the substrate and inhibitor compete for binding to the same active site or
• noncompetitively, when the inhibitor binds somewhere else on the enzyme molecule reducing its efficiency.

The distinction can be determined by plotting enzyme activity with and without the inhibitor present.

Competitive Inhibition

In the presence of a competitive inhibitor, it takes a higher substrate concentration to achieve the same velocities that were reached in its absence. So while V_max can still be reached if sufficient substrate is available, one-half V_max requires a higher [S] than before and thus K_m is larger.

Noncompetitive Inhibition

With noncompetitive inhibition, enzyme molecules that have been bound by the inhibitor are taken out

• enzyme rate (velocity) is reduced for all values of [S], including
• V_max and one-half V_max but
• K_m remains unchanged because the active site of those enzyme molecules that have not been inhibited is unchanged.

COPPER

The normal serum level of copper is 25 to 50 mg/dl.

Functions of copper

(a) Copper is necessary for iron absorption and incorporation of iron into hemoglobin.

(b) It is very essential for tyrosinase activity

(c) It is the co-factor for vitamin C requiring hydroxylation

(d) Copper increases the level of high density lipo protein and protects the heart.

Wilson’s disease

In case of Wilson’s disease ceruloplasmin level in blood is drastically reduced.

Wilson’s disease leads to

(i) Accumulation of copper in liver leads to hepatocellular degeneration and cirrhosis

(ii) Deposition of copper in brain basal ganglia leads to leticular degeneration

(iii) Copper deposits as green pigmented ring around cornea and the condition is called as Kayser-Kleischer ring

Over accumulation of copper can be treated by consumption of diet containg low copper and injection of D-penicillamine, which excretes copper through urine.

Menke’s kidney hair syndrome

 It is X-linked defect. In this condition copper is absorbed by GI tract, but cannot be transported to blood. The defect in transport of copper to blood is due to absence of an intracellular copper binding ATPase.

Glycogen Storage Diseases are genetic enzyme deficiencies associated with excessive glycogen accumulation within cells.

• When an enzyme defect affects mainly glycogen storage in liver, a common symptom is hypoglycemia (low blood glucose), relating to impaired mobilization of glucose for release to the blood during fasting.
• When the defect is in muscle tissue, weakness and difficulty with exercise result from inability to increase glucose entry into Glycolysis during exercise.

Various type of Glycogen storage disease are

Role of Coenzymes

The functional role of coenzymes is to act as transporters of chemical groups from one reactant to another.

Ex. The hydride ion (H+ + 2e-) carried by NAD or the mole of hydrogen carried by FAD;

The amine (-NH2) carried by pyridoxal phosphate