Discussion on Respiration In Plants


 

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Posted on: 11:16:00 AM on July 3, 2013
how glycolysis occurs


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Posted on: 01:23:49 AM on July 4, 2013
Step 1 The enzyme hexokinase phosphorylates (adds a phosphate group to) glucose in the cell's cytoplasm. In the process, a phosphate group from ATP is transferred to glucose producing glucose 6-phosphate. Glucose (C6H12O6) + hexokinase + ATP → ADP + Glucose 6-phosphate (C6H11O6P1) Step 2 The enzyme phosphoglucoisomerase converts glucose 6-phosphate into its isomer fructose 6-phosphate. Isomers have the same molecular formula, but the atoms of each molecule are arranged differently. Glucose 6-phosphate (C6H11O6P1) + Phosphoglucoisomerase → Fructose 6-phosphate (C6H11O6P1) Step 3 The enzyme phosphofructokinase uses another ATP molecule to transfer a phosphate group to fructose 6-phosphate to form fructose 1, 6-bisphosphate. Fructose 6-phosphate (C6H11O6P1) + phosphofructokinase + ATP → ADP + Fructose 1, 6-bisphosphate (C6H10O6P2) Step 4 The enzyme aldolase splits fructose 1, 6-bisphosphate into two sugars that are isomers of each other. These two sugars are dihydroxyacetone phosphate and glyceraldehyde phosphate. Fructose 1, 6-bisphosphate (C6H10O6P2) + aldolase → Dihydroxyacetone phosphate (C3H5O3P1) + Glyceraldehyde phosphate (C3H5O3P1) Step 5 The enzyme triose phosphate isomerase rapidly inter-converts the molecules dihydroxyacetone phosphate and glyceraldehyde phosphate. Glyceraldehyde phosphate is removed as soon as it is formed to be used in the next step of glycolysis. Dihydroxyacetone phosphate (C3H5O3P1) → Glyceraldehyde phosphate (C3H5O3P1) Net result for steps 4 and 5: Fructose 1, 6-bisphosphate (C6H10O6P2) ↔ 2 molecules of Glyceraldehyde phosphate (C3H5O3P1) Step 6 The enzyme triose phosphate dehydrogenase serves two functions in this step. First the enzyme transfers a hydrogen (H-) from glyceraldehyde phosphate to the oxidizing agent nicotinamide adenine dinucleotide (NAD+) to form NADH. Next triose phosphate dehydrogenase adds a phosphate (P) from the cytosol to the oxidized glyceraldehyde phosphate to form 1, 3-bisphosphoglycerate. This occurs for both molecules of glyceraldehyde phosphate produced in step 5. A. Triose phosphate dehydrogenase + 2 H- + 2 NAD+ → 2 NADH + 2 H+ B. Triose phosphate dehydrogenase + 2 P + 2 glyceraldehyde phosphate (C3H5O3P1) → 2 molecules of 1,3-bisphosphoglycerate (C3H4O4P2) Step 7 The enzyme phosphoglycerokinase transfers a P from 1,3-bisphosphoglycerate to a molecule of ADP to form ATP. This happens for each molecule of 1,3-bisphosphoglycerate. The process yields two 3-phosphoglycerate molecules and two ATP molecules. 2 molecules of 1,3-bisphoshoglycerate (C3H4O4P2) + phosphoglycerokinase + 2 ADP → 2 molecules of 3-phosphoglycerate (C3H5O4P1) + 2 ATP Step 8 The enzyme phosphoglyceromutase relocates the P from 3-phosphoglycerate from the third carbon to the second carbon to form 2-phosphoglycerate. 2 molecules of 3-Phosphoglycerate (C3H5O4P1) + phosphoglyceromutase → 2 molecules of 2-Phosphoglycerate (C3H5O4P1) Step 9 The enzyme enolase removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvic acid (PEP). This happens for each molecule of 2-phosphoglycerate. 2 molecules of 2-Phosphoglycerate (C3H5O4P1) + enolase → 2 molecules of phosphoenolpyruvic acid (PEP) (C3H3O3P1) Step 10 The enzyme pyruvate kinase transfers a P from PEP to ADP to form pyruvic acid and ATP. This happens for each molecule of PEP. This reaction yields 2 molecules of pyruvic acid and 2 ATP molecules. 2 molecules of PEP (C3H3O3P1) + pyruvate kinase + 2 ADP → 2 molecules of pyruvic acid (C3H4O3) + 2 ATP Summary In summary, a single glucose molecule in glycolysis produces a total of 2 molecules of pyruvic acid, 2 molecules of ATP, 2 molecules of NADH and 2 molecules of water. Although 2 ATP molecules are used in steps 1-3, 2 ATP molecules are generated in step 7 and 2 more in step 10. This gives a total of 4 ATP molecules produced. If you subtract the 2 ATP molecules used in steps 1-3 from the 4 generated at the end of step 10, you end up with a net total of 2 ATP molecules produced. For a detailed view of the 10 steps, see: Details of the 10 Steps of Glycolysis.



Posted on: 10:37:10 AM on July 4, 2013
thanks for ur valuable response to my doubt





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