Conclusion is. therefore in anaerobic catabohsm of glucose, laclic acid accumulates in the blood Thus

other coenzymes are regenerated (i e they become free to catch H atom again) If 02 is not available (eg in anona), the NADH cannot unload it's H atom [hydrogen combines with oxygen to form water] and go conversion of phosp ho glycef aldehyde Into diphosphoglycerate can no longer occur and the EMP should stop A compensatory mechanism exists by which NADH can unload its Hatom, as follows The end product of EMP 15 pyruvic acid [table 7.6.1) NADH unloads The H atom into the pyruvic acid, converting it into lactic acid and The NAD* is regenerated, The reaction is catalyzed by lactale dehyd'ogenase . Conclusion is. therefore in anaerobic catabohsm of glucose, laclic acid accumulates in the blood Thus after 3 100 meter sprinting, a prize lighter's blood lactale concentration may rise to such values like 200 mg/100 ml (normal value at rest about 5 mg/100 ml] For further details, see physiology of exercise (chap 93) Limitation or anerobc catabohsm of glucose Formation of lacttc acid can ens ure the continuation of EMP fof sometime, but not for long time As the concentration of blood lactate uses, the individual is forced to stop exercise. [By contrast, in the steady state of muscular exercise, e';g running slowly, there is no lack of 02 Krebs Cycle operates fully, tactic acid does not accumulate appreciably, and the exercise can be continued for long spell] Utility of anerobic catabolism of glucose When i hunted animal is running for life it has no time for breathing or, even if he is able to breaihe, the amount of 01 may be insufficient (see oxygen debt chap 9.3) Anerobic metabolism of glucose and formation of lactic acid gives him a chance To tide over the crisis. Similar circumstances occur in human beings, e g during emergency, sports etc. The polar animal, 'seal' which is a land mammal, when dives in water and chases a fish undarwuler, might have to remain several minutes under waler, struggling with the fish At such times, the animal can develop a phenomenal blood lactale concentration (see also 'diving reflex1 in cardiovascular physiology, chap 5.4) Con Cycle During anaerobic exercise, thus, lactic acid accumulates in the muscle Some of this lactic acid escapes into the blood and reaches the liver where the latic acid by glurnneogenesis. is converted into liver glycogen. Neatly, the liver glycogen, by glycogenotysis. becomes glucose and is released into blood. This glucose, borne by blood, now appears back in the exercising muscle and so the EMP and generation of ATP within the muscEe are maintained to some extent despite the anoxia This is Cori Cycle (named after the American biochemist GT Con and his wife) Fig 762 Con's cycle Energy Yield during EMP As stated already [dunng the discussion on steps of EMP], 4 molecules of ATP are produced in addition to 4 atoms of H released. however where glucose is the starting material, 2 molecutes of ATP are expended also Transfer of each 2 atoms of H yield 3 molecules of ATP so that 4 atoms of H become equivalent lo 6 ATP molecules The number of ATP gamed is thus. (A * E - 2) = 8 molecules per single molecule of glucose However, if the starting material is glycogen, the gain is 9 molecules per 6 C atoms as 1 molecule of ATP in step I is saved Conversion of pyruvic acid to active acetate Pyruvic acid is subsequently converted into active acetate, according lo the equation given below CK3CC COOH + HSCoA o CK3CO S CoA + C02 +2H [Pyruvic a) (Coenzyme A) (H accepted by NAO+J Acetyl coenzyme A is popularly called "acfive acetate'. The reaction, as shown above is irreversible and catalyzed by pyruvare dehydrogenase [Actually, pyruvale dehydrogenase is a complex of enzymes and the above shown reaction occurs in several stages). In the above shown reaction, thiamine pyrophosphate' (TPP), [a coenzy/tne derived from vitamin BTJ, and lipoic acrd must be present as cofactor. In severe deficiency of vit Bl (ben ben), therefore, pyruvic acid accumulates in blood (normal value, about 0.5 mg/100 ml). Rise of Wood pyruvtc acid at rest ishtheraforeh diagnostic of vit Bl deficiency As shown above, conversion of pyruvate to active acetate releases 2 atoms of H (- 1 molecules of ATP). Two molecules of pyruvic acid (= one molecule of glucose), therefore, yields 4 H (-^G molecules of ATP) atoms Fale of active acetate This has been discussed in detail in a. later chapter of this section For the time being it may be noted that most of the active acetate molecules enter Krebs cycle. KREBS CYCLE (ALSO CALLED CITRIC AClD' OR TRICARBQXYUC ACID' CYCLE) Introduction Site and major sleps. Control of Krebs cycle Energy Yield. Concept of a final common path. Amphibolic role of Krebs Cycle. Applied biochemistry Introduction As staled earlier, pyruvic acid formed from EMP is converted into active acetate which is a 2 C1 structure Active acelale unites with oxaloacetic acid (OAA). [which is 4 "C1 structure) so that citric acid, a 'J '! structure containing three carboxyl, COOH radicals (hence the names, citric acid qt tricar box ylic acid cycle) is Formed This 6 'C1 structure (i e citric acid) undergoes a senes of changes brought by enzymatic catalysis, so that it loses 2 C atoms to become the 4 HC' structure, that is. OM again The two 'C' aloms escape as C02 and the associated H atoms are removed by respiratory chain (hydrogen transfer system) The CD2 is eventually handed over to the venous blood and escapes via the lungs, whereas the H atoms form waler and removed as unne/sweal elc The carnage of H atoms yreld la