Anaerobic organisms lack a respiratory chain. They must reoxidize NADH produced in Glycolysis through some other reaction, because NAD⁺ is needed for the Glyceraldehyde-3-phosphate Dehydrogenase reaction (see above). Usually NADH is reoxidized as pyruvate is converted to a more reduced compound, that may be excreted.

The complete pathway, including Glycolysis and the re-oxidation of NADH, is called fermentation.

For example, Lactate Dehydrogenase catalyzes reduction of the keto group in pyruvate to a hydroxyl, yielding lactate, as NADH is oxidized to NAD⁺.

Skeletal muscles ferment glucose to lactate during exercise, when aerobic metabolism cannot keep up with energy needs. Lactate released to the blood may be taken up by other tissues, or by muscle after exercise, and converted via the reversible Lactate Dehydrogenase back to pyruvate

Fermentation Pathway, from glucose to lactate (omitting H⁺):

   glucose + 2 ADP + 2 P_i → 2 lactate + 2 ATP

Anaerobic catabolism of glucose yields only 2 “high energy” bonds of ATP.

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

Ampholytes, Polyampholytes, pI and Zwitterion

Many substances in nature contain both acidic and basic groups as well as many different types of these groups in the same molecule. (e.g. proteins). These are called ampholytes (one acidic and one basic group) or polyampholytes (many acidic and basic groups). Proteins contains many different amino acids some of which contain ionizable side groups, both acidic and basic. Therefore, a useful term for dealing with the titration of ampholytes and polyampholytes (e.g. proteins) is the isoelectric point, pI. This is described as the pH at which the effective net charge on a molecule is zero.

For the case of a simple ampholyte like the amino acid glycine the pI, when calculated from the Henderson-Hasselbalch equation, is shown to be the average of the pK for the a-COOH group and the pK for the a-NH₂ group:

pI = [pK_a-(COOH) + pK_a-(NH3⁺₎]/2

For more complex molecules such as polyampholytes the pI is the average of the pK_a values that represent the boundaries of the zwitterionic form of the molecule. The pI value, like that of pK, is very informative as to the nature of different molecules. A molecule with a low pI would contain a predominance of acidic groups, whereas a high pI indicates predominance of basic groups.

Monosaccharides: Aldoses (e.g., glucose) have an aldehyde at one end

They are classified acc to the number of carbon atoms present

Trioses, tetroses, pentose ( ribose, deoxyribose), hexoses  (glucose, galactose, fructose) Heptoses (sedoheptulose)

Glyceraldehyde simplest aldose

Ketoses (e.g., fructose) have a keto group, usually at C 2.

Dihydroxyacetone simplest Ketoses

The higher sugar exists in ring form rather than chain form

Furan  : 4 carbons and 1 oxygen

Pyrans : 5 carban and 1 oxygen

 These result from formation of hemiacital linkage b/w carbonyl and an alcohol group

Regulation of PTH secretion

Secretion of parathyroid hormone is controlled chiefly by serum [Ca²⁺] through negative feedback. Calcium-sensing receptors located on parathyroid cells are activated when [Ca²⁺] is low.

Hypomagnesemia inhibits PTH secretion and also causes resistance to PTH, leading to a form of hypoparathyroidism that is reversible.

Hypermagnesemia also results in inhibition of PTH secretion.

Stimulators of PTH includes decreased serum [Ca²⁺], mild decreases in serum [Mg²⁺], and an increase in serum phosphate.

Inhibitors include increased serum [Ca²⁺], severe decreases in serum [Mg²⁺], which also produces symptoms of hypoparathyroidism (such as hypocalcemia), and calcitriol.

These cannot be synthesized by the body and must be obtained from food.

Found in: Meat, eggs, dairy, soy, legumes, quinoa