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Question : Describe anaerobic phase of aerobic respiration |
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Answer» Solution : Definition : Glycolysis means the phase till formation of two molecules of pyruvic acid from one molecule of glucose takes place. Origin : The term glycolysishas originated form the Greek words glucose form sugar and lysis for splitting. The scheme of glycolysis was given by Gustav Embden, OttoMeyercdofand J. Parnas and is often referred to as the EMP pathway. In anaerobic organisms, only glycolysisoccurs. Glycolysisoccurs in the cytoplasm of the cell and in thisprocess undergoes partial oxidation toform two molecules of pyruvic acid . In plants, this glucose is derived from sucrose . whichis theend productof photosynthesis or from storagecarbohydrates. Both these monosaccharidesreadilyenter the glycolytic pathway. Glucose and fructose are phosphorylated to give rise to Glucose-6- phosphateby theactivity of the enzyme hexokinase. Glucose + ATP `overset("Hexokinase")to ` Glucose-6-Phosphate Thisphosphorylated form of glucose then isomerises toproduce fructose-6- phosphate. Glucose-6- Phosphate `to` Fructose-6- Phosphate Subsequentsteps of metabolism of glucoseand fructose are same. Inglycolysis, a chain of TEN reactions, under the control of differentenzymes, takesplace toproducepyruvate from glucose. Nowfructose-6- phosphate is converted into fructose-1, 6 -biphosphate in presence of ATP. ATP is utilised at two steps. First in the conversion of glucose into glucose 6-phosphate an in second stepthe conversion of fructose 6-phosphate to fructose 1, e-biphosphate. Now the fructose 1,6-biphosphate is split into dihydroxyacetone phosphate and3-phosphoglyceraldehyde (PGAL). Fructose 1, 6-Biphosphate `to ` DHAP(3G) + PGAL (3G) There isone STEP where NADH + `H^(+)`is formed from `NAD^(+)`,this is when 3-phosphoglyceraldehyde is converted to 1,3-biphosphoglycerate (BPGA). 3-phosphoglyceraldehyde `to` 1,3-biphosphoglycerate + NADH `+ H^(+)` Two redox-equivalents are removed (in the form of hydrogen atoms) from PGAL, and transferred to a molecule of `NAD^(+)` PGAL is oxidisedand with inorganic phosphate to get converted intoBPGA. Theconversion of BPGA to 3-phosphoglyceric acid (PGA) ,is also an energy yielding process. This energy is trapped by the formation of ATP Another ATP is SYNTHESISED during the conversion of PEP to pyruvic acid . (Formationof ATP = 4ATP mode) Pyruvicacid is then the key productof glycolysis. Whatis he metabolic fate of pyruvate ? depends on the cellular need. There are three major ways in which differentcells handle pyruvic acid produced by glycolysis (1) Lactic acid FERMENTATION. (2) Alcoholic fermentation. (3) Aerobic respiration. fermentation takes place under anaerobic conditions in many prokaryotes and unicellular eukaryotes. For the complete oxidation of glucose to `CO_(2)and H_(2)O`, however, organisms adopt Kreb, cycle which is also calledas aerobic respiration. This requires `O_(2)`supply. 
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