NEET MDS Lessons
Biochemistry
Glycogen Metabolism
The formation of glycogen from glucose is called Glycogenesis
Glycogen is a polymer of glucose residues linked mainly by a(1→ 4) glycosidic linkages. There are a(1→6) linkages at branch points. The chains and branches are longer than shown. Glucose is stored as glycogen predominantly in liver and muscle cells
Glycogen Synthesis
Uridine diphosphate glucose (UDP-glucose) is the immediate precursor for glycogen synthesis. As glucose residues are added to glycogen, UDP-glucose is the substrate and UDP is released as a reaction product. Nucleotide diphosphate sugars are precursors also for synthesis of other complex carbohydrates, including oligosaccharide chains of glycoproteins, etc.
UDP-glucose is formed from glucose-1-phosphate and uridine triphosphate (UTP)
glucose-1-phosphate + UTP → UDP-glucose + 2 Pi
Cleavage of PPi is the only energy cost for glycogen synthesis (1P bond per glucose residue)
Glycogenin initiates glycogen synthesis. Glycogenin is an enzyme that catalyzes glycosylation of one of its own tyrosine residues.
Physiological regulation of glycogen metabolism
Both synthesis and breakdown of glycogen are spontaneous. If glycogen synthesis and phosphorolysis were active simultaneously in a cell, there would be a futile cycle with cleavage of 1 P bond per cycle
To prevent such a futile cycle, Glycogen Synthase and Glycogen Phosphorylase are reciprocally regulated, both by allosteric effectors and by covalent modification (phosphorylation)
Glycogen catabolism (breakdown)
Glycogen Phosphorylase catalyzes phosphorolytic cleavage of the →(1→4) glycosidic linkages of glycogen, releasing glucose-1-phosphate as the reaction product.
Glycogen (n residues) + Pi → glycogen (n-1 residues) + glucose-1-phosphate
The Major product of glycogen breakdown is glucose -1-phosphate
Fate of glucose-1-phosphate in relation to other pathways:
Phosphoglucomutase catalyzes the reversible reaction:
Glucose-1-phosphate → Glucose-6-phosphate
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.
Vitamin B12: Cobalamin
Vitamin B12, also known as cobalamin, aids in the building of genetic material, production of normal red blood cells, and maintenance of the nervous system.
RDA The Recommended Dietary Allowance (RDA) for vitamin B12 is 2.4 mcg/day for adult males and females
Vitamin B12 Deficiency
Vitamin B12 deficiency most commonly affects strict vegetarians (those who eat no animal products), infants of vegan mothers, and the elderly. Symptoms of deficiency include anemia, fatigue, neurological disorders, and degeneration of nerves resulting in numbness and tingling.
SELENIUM
normal serum level is 50-100 mg/day
Selenium dependent enzymes include glutathione Peroxidase and 5-de-iodinase. Selenium concentration in testis is the highest in adult. It is very necessary for normal development and maturation of sperm.
By rearranging the above equation we arrive at the Henderson-Hasselbalch equation:
pH = pKa + log[A-]/[HA]
It should be obvious now that the pH of a solution of any acid (for which the equilibrium constant is known, and there are numerous tables with this information) can be calculated knowing the concentration of the acid, HA, and its conjugate base [A-].
At the point of the dissociation where the concentration of the conjugate base [A-] = to that of the acid [HA]:
pH = pKa + log[1]
The log of 1 = 0. Thus, at the mid-point of a titration of a weak acid:
pKa = pH
In other words, the term pKa is that pH at which an equivalent distribution of acid and conjugate base (or base and conjugate acid) exists in solution.
STEROIDS
Steroids are the compounds containing a cyclic steroid nucleus (or ring) namely cyclopentanoperhydrophenanthrene (CPPP).It consists of a phenanthrene nucleus (rings A, B and C) to which a cyclopentane ring (D) is attached.
Steroids are the compounds containing a cyclic steroid nucleus (or ring) namely cyclopentanoperhydrophenanthrene (CPPP).It consists of a phenanthrene nucleus (rings A, B and C) to which a cyclopentane ring (D) is attached.
There are several steroids in the biological system. These include cholesterol, bile acids, vitamin D, sex hormones, adrenocortical hormones,sitosterols, cardiac glycosides and alkaloids
IONIZATION OF WATER, WEAK ACIDS AND WEAK BASES
The ionization of water can be described by an equilibrium constant. When weak acids or weak bases are dissolved in water, they can contribute H+ by ionizing (if acids) or consume H+ by being protonated (if bases). These processes are also governed by equilibrium constants
Water molecules have a slight tendency to undergo reversible ionization to yield a hydrogen ion and a hydroxide ion :
H2O = H+ + OH−
The position of equilibrium of any chemical reaction is given by its equilibrium constant. For the general reaction,
A+B = C + D