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

Thiamin: Vitamin B1

Thiamin, or vitamin B1, helps to release energy from foods, promotes normal appetite, and is important in maintaining proper nervous system function.

RDA (Required Daily allowance) Males: 1.2 mg/day; Females: 1.1 mg/day

Thiamin Deficiency

Symptoms of thiamin deficiency include: mental confusion, muscle weakness, wasting, water retention (edema), impaired growth, and the disease known as beriberi.

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.

TRIGLYCEROL

Triacylglycerols (formerly triglycerides) are the esters of glycerol with fatty acids. The fats and oils that are widely distributed in both  plants and animals are chemically triacylglycerols.

They are insoluble in water and non-polar in character and commonly known as neutral fats.

Triacylglycerols are the most abundant dietary lipids. They are the form in which we store reduced carbon for energy. Each triacylglycerol has a glycerol backbone to which are esterified 3 fatty acids. Most triacylglycerols are "mixed." The three fatty acids differ in chain length and number of double bonds

Structures of acylglycerols :

Monoacylglycerols,  diacylglycerols and triacylglycerols, respectively consisting of one, two and three molecules of fatty acids esterified to

a molecule of glycerol

Lipases hydrolyze triacylglycerols, releasing one fatty acid at a time, producing  diacylglycerols, and eventually glycerol

Glycerol arising from hydrolysis of triacylglycerols is converted to the Glycolysis intermediate dihydroxyacetone phosphate, by reactions catalyzed by:
(1) Glycerol Kinase
(2) Glycerol Phosphate Dehydrogenase

Free fatty acids, which in solution have detergent properties, are transported in the blood bound to albumin, a serum protein produced by the liver.
Several proteins have been identified that facilitate transport of long chain fatty acids into cells, including the plasma membrane protein CD36

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

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.