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| Mechanism of Respiration |
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| Human cellular respiration can be divided into 2 main phases. |
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| a) Glycolysis |
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| b) Kreb's cycle |
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| The Broad Scheme of Respiration |
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| The Steps of Respiration at a Glance |
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| Glycolysis |
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| It is a common series of steps for both aerobic and anaerobic respiration. It is a process by which glycogen or glucose or other sugars are converted into pyruvic acid. This process does not utilise oxygen. Glycolysis is also called as EMP path way or EMBEN, MEYERHOF and PARNAS pathway as the various steps have been worked out by the two German biochemists. |
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| Various Steps Involved In the Process of Glycolysis |
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| Steps in glycolysis |
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| 1) Glucose in the cells is phosphorylated by ATP in the presence of gluco hexokinase to form glucose-6-phosphate. |
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| 2) Glucose-6-phosphate is then converted into fructose-6-phosphate by the enzyme glucose phosphate isomerase. |
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| 3) Fructose-6-phosphate is then phosphorylated by ATP in the presence of phospho fructokinase to form fructose 1,6,diphosphate. |
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| 4) The fructose 1, 6-diphosphate is split into 2 substances namely glyceraldehydes 3 phosphate and dihydroxyacetone phosphate. These 2 substances are inter convertible in the presence of triose phosphate isomerase. |
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| 5) The 2 molecules of glyceraldehydes phosphate are phosphorylated and oxidised into 2 molecules of 1,3-diphosphoglyceric acid catalysed by the enzyme phosphoglyceraldehyde dehydrogenase. NAD and inorganic phosphates are required. 1,3-diphosphoglyceraldehyde is the possible intermediate product. |
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| 6) 1,3-diphospho glyceric acid is converted into 3-phospho glyceric acid by means of phospho glycerate kinase in the presence of Mg++. |
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| 7) 3-phosphoglyceric acid is converted into 2-phosphoglyceric acid by the enzyme phosphoglyceromutase. |
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| 8) 2-phosphoglyceric acid is converted into phsophoenol pyruvic acid by dehydration in the presence of enolase. |
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| 9) The phosphoenol pyruvic acid transfers its energy rich phosphate to ADP under the influence of phospho pyruvate kinase and in the presence of Mg++ and K+ forming enolypyruvic acid and ATP. The enol pyruvic acid is spontaneously transformed into pyruvic acid. |
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| Pyruvic acid is the main end product of animal tissues, which are supplied with sufficient O2. |
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| Thus during glycolysis, each molecule of glucose yields 2 molecules of pyruvic acid with the formation of 10 molecules of ATP. |
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| Energetics of glycolysis |
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| During glycolysis of each molecule of glucose, 2 ATP molecules are utilised and 10 molecules of ATP are synthesized. Hence there is a net gain of 8 molecules of ATP during glycolysis. |
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| In the Glycolysis pathway, the molecules of ATP are produced in two ways: |
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| 1) Direct transfer of phosphate to ADP and |
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| 2) Oxidation of NADH produced during glycolysis to NAD+. |
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| Each molecule of NADH gives rise to 3 molecules of ATP. In glycolysis, 2-triose phosphates molecular are formed from one glucose molecule and 4 ATP molecules are produced. Out of these 4 ATP molecules, 2 are consumed initially in converting glucose to fructose 1-6 diphosphate. Three molecules each of ATP are produced from the oxidation of 2 molecules of NADH. Transfer a net gain of 8 ATP molecules occurs during glycolysis. |
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| The ATP utilisation and synthesis during glycolysis are summarised below: |
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| Functions of Glycolysis |
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| a) It is only in this process glucose is converted into pyruvic acid. |
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| b) The intermediate products formed in glycolysis are utilized for the synthesis of fat. |
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| c) It also yields some energy in the form of ATP. |
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