Glycogenolysis

Breakdown of  glycogen to glucose is called glycogenolysis. The Breakdown of glycogen takes place in liver and muscle. In Liver , the end product of glycodgen breakdown is glucose where as in muscles the end product is Lactic acid Under the combined action of Phosphorylase  (breaks only –α-(1,4) linkage )and Debranching enzymes (breaks only α-(1,6) linkage )glycogen is broken down to glucose.

Weak Acids and pKa

• The strength of an acid can be determined by its dissociation constant, Ka.

• Acids that do not dissociate significantly in water are weak acids.

• The dissociation of an acid is expressed by the following reaction: HA = H⁺ + A^- and the dissociation constant Ka = [H⁺ ][A^- ] / [HA]  

• When Ka < 1, [HA] > [H⁺ ][A^- ] and HA is not significantly dissociated. Thus, HA is a weak acid when ka < 1.

• The lesser the value of Ka, the weaker the acid.

• Similar to pH, the value of Ka can also be represented as pKa.

• pKa = -log Ka.

• The larger the pKa, the weaker the acid.

• pKa is a constant for each conjugate acid and its conjugate base pair.

• Most biological compounds are weak acids or weak bases.

LIPIDS

The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, which are related more by their physical than by their chemical properties.

Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents.

Most membrane lipids are amphipathic, having a non-polar end and a polar end

Lipids are important in biological systems because they form the cell membrane, a mechanical barrier that divides a cell from the external environment.

Lipids also provide energy for life and several essential vitamins are lipids.

Lipids can be divided in two major classes, nonsaponifiable lipids and saponifiable lipids.

A nonsaponifiable lipid cannot be broken up into smaller molecules by hydrolysis, which includes triglycerides, waxes, phospholipids, and sphingolipids.

A saponifiable lipid contains one or more ester groups allowing it to undergo hydrolysis in the presence of an acid, base, or enzyme.

Nonsaponifiable lipids include steroids, prostaglandins, and terpenes

Nonpolar lipids, such as triglycerides, are used for energy storage and fuel.

Polar lipids, which can form a barrier with an external water environment, are used in membranes.

Polar lipids include glycerophospholipids and sphingolipids.

Fatty acids are important components of all of these lipids.

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.

Factors regulating blood calcium level

(i) Vitamin D

(a) Vitamin D and absorption of calcium: Active form of calcium is calcitriol. Calcitriol enters intestinal wall and binds to cytoplasmic receptor and then binds with DNA causes depression and consequent transcription of gene code for calbindin. Due to increased availability of calbindin, absorption of calcium increases leading to increased blood calcium level.
(b) Vitamin D and Bone: Vitamin D activates osteoblast, bone forming cells & also stimulates secretion of alkaline phosphatase. Due to this enzyme, calcium and phosphorus increase.

(c) Vitamin D and Kidney: Calcitriol increase reabsorption of calcium and phosphorus by renal tubules.

(ii) Parathyroid  hormone (PTH)

Normal PTH level in serum is 10-60ng/l.

(a) PTH and bones: In bone, PTH causes demineralization. It also causes recreation of collagenase from osteoclast  leads to loss of matrix and bone resorption. As a result, mucopolysacharides and hydroxyproline are excreted in urine.

(b) PTH and Kidney: In kidney, PTH causes increased reabsorption of calcium but decreases reabsorption of phosphorus from kidney tubules.

(iii) Calcitonin Calcitonin decreases serum calcium level. It inhibits resorption of bone. It decreases the activity of osteoclasts and increases osteoblasts.

Hyper Calcemia When plasma Ca2+ level is more than 11mg/dl is called Hypercalcemia. It is due to parathyroid adenoma or ectopic PTH secreting tumor. calcium excreted in urine decreases excretion of chloride causing hyperchloremic acidosis.

Hypocalcemia Plasma calcium level less than 8mg/dl is called hypocalcemia. Tetany due to accidental surgical removal of parathyroid glands or by autoimmune disease. In tetany, neuromuscular irritability is increased. Increased Q-7 internal in ECG is seen. Main manifestation is carpopedal spasm. Laryngismus and stridor are also observed.

The basic characteristics of enzymes includes

(i) Almost all the enzymes are proteins and they follow the physical and chemical reactions of proteins (ii) Enzymes are sensitive and labile to heat

(iii) Enzymes are water soluble

(iv) Enzymes could be precipitated by protein precipitating agents such as ammonium sulfate and trichloroacetic acid.