played by the hormones discussed. Blood Sugar Regulation Role of major hormones. (i) Insulin causes hypoglycemia severe hypoglycemia can lead to convu

played by the hormones discussed. Blood Sugar Regulation Role of major hormones. (i) Insulin causes hypoglycemia severe hypoglycemia can lead to convulsion; (a) glycogenolysis inhibited because phosptiokinase activity and hence phosphorylase a formation inhibited by insulin (b) glycogenesis stimulated (because glycogen synthase activity stimulated) (c) gluconetogenesis inhibited insulin also (d) increases glucose entry and (e) prevents ketosis. (2) Cortisol raises blood sugar by stimulating glucone agenesis and reducing peripheral utilization (but it also increases hepatic glycogenesis). (3) Glucagon causes increased glycogenolysis (only in liver) and gluconeogenesis (4) Adrenalin increases glycogenolysis (muscle + liver), lipolysis (which reduces glucose ntry within cell) and gluconeogenesis (5) On the whole , thyroxine raises blood sugar. Introduction EMP 3. Krebs cycle HMP. Uronic acid pathway. Introduction As already stated, glucose, when completely calabolized, yields H20 and C02 plus some energy. A portion of the energy is converted into ATP and the rest appears as heal. The catabolic steps may be divided into two traditional major stages. (A) glycolytic pathway (or Embden Meyerhof pathway, EMP), end product of EMP is pyruvic acid (when OZ supply to tissue is satisfactory) or lactic acid (when 02 supply is absent or deficient), and (9) Krebs cycle (after HA Krebs, who was awarded a Nobel Prize for his works on metabolism Krebs cycle is also called citric acid cycle or tricarboxylic acid cycle). The end products of Kreos cycle are CO2 and water. There is an alternative path, called the 'hexose monophosphate shunt or pathway' (HMS or HMP) by which glucose can be catabalized without going through the EMP However, as will be described afterwards, it appears that the major aim of HMP is to generator raw materials for fatty acid, nucleic acid and nucleotide synthesis rather than to generate energy. It will be seen that both the EMP and Krebs cycle can be viewed as mechanism which cause release of H atoms from the substrates. These H atoms are subsequently carried by hydrogen carrier system (for details see fig 7.2.1) so that H20 plus large amount of energy are formed, the energy is concomitantly trapped and ATP molecules are formed by adding a phosphate radical (phosphorylatig) to ADP EMBDEN MEYERHOF PATHWAY Site. Steps. Formation of lactic acid. Con's cycle. Energy yield. Sites Catabolism of glucose via EMP occurs mainly in the brain , RBC and muscles, in the last named during hard ex-ercise. In the RBC. the glucose cannot however be metabolized beyond the EMP as the arrangements for the Krebs cycle (presence of mitochondria) do not exist in the RBCs. Catabolism via HMP occurs notably in adipose tissue as well as in mammary glands and to some extent in the liver. It is to be noted that, in most of the tissues, glucose catabolsim occurs and occurs via EMP, brain. RBC and exercising muscles are only special examples. Steps The steps have been shown in the accompanying table (Table 7.6.1) 1. The starting point of EMP may be glucose (as in brain or RBC. who get glucose directly from blood) or glycogen (as in muscles or liver). If the starting material is glycogen. the first step is formation of glucose. 1. phos (ie. ester formation between - OH radical and photshoric acid, occurs at C1 level), as described already in glycogenolysis. The phosphate donor is inorganic phosphate. But if the starting material is glucose, the first step is conversion of glucose into gl 6 phos, glucokinase (in liver only) or hexokinase (in other issues) actig as the enzyme. The process is called 'phosphorylation' Fig. 7.6.1 ATP is the phosphate donor in this reaction, that is, one molecule of ATP has to be broken down to start the EMP Subsequently, for conversion of fructose & phos to fr 1,6, phos (step III in Table 7.6.1) another molecule of ATP is to be broken down 3. At step VI ie. during conversion of each molecule of diphosphoglycerate to monophosphoglycerate, one molecule of high energy phosphate radical is released and utilized for conversion of ADP into ATP. As two molecules of diphosphogIycerate (3 C structure) are formed from one molecule of gl 6 phos (6 C structure), two molecules of ATP are formed 4. At step IX, i.e, during conversion of phosphcenol pyruvate to enol form of pyruvate another molecule of ATP for each 3'C structure,is generated 5 At sup V (conversion of mono) phosphoglyceraldehyde to diphosphoglyceric acid). 2 atoms of hydrogen per 3C structure are released. This means, per 6C (glucose) structure, 4 atoms of H are released. Each released H atoms are carried via hydrogen (electron) transfer system (fig 7.2.1) and during the journey of hydrogen to unite witn oxygen (to form H2O),3 ATP molecules are generated per every 2 H atoms. Steps I (glucose to gl6 phosj\). Ill, IX and X are not reversible. As already stated while discussing gluconeogenesis, the gluconeoganic path is largely (but not entirely) a reverse path in the EMP However, as mentioned above, some of the EMP steps are non reversible and special enzymes act in these steps. Formation of lactic acid Con Cycle At step V (Table 7.6.1) of EMP, i e . during conversion of glyceraldehyde phosphate into 1.3 diphosphoglycerate, as stated already. 2H atoms are released. These H atoms are taken up by NAD+, the coeozyme, which in turn becomes NADH (reduced NAD+) Subsequently, the H atom moves down the hydrogen (electron) transfer system and forms H20. Thus the NAD+ and the