Chapter 27 Specific Catabolic Pathways: Carbohydrate, Lipid & Protein Metabolism

Glycolysis: Follow Along: Figure 27.3

Glycolysis 10 enzyme-catalyzed reactions by which glucose is oxidized to two molecules of pyruvate. During glycolysis, there is net conversion of 2ADP to 2ATP. NOTE: ATP = Energy molecule of choice

Glycolysis - Rxn 1 reaction 1: reaction 1: phosphorylation of  -D-glucose.

Glycolysis - Rxn 2 reaction 2: reaction 2: isomerization of glucose 6-phosphate to fructose 6-phosphate.

Glycolysis - Rxn 2 This isomerization is most easily seen by considering the open-chain forms of each monosaccharide; it is one keto-enol tautomerism followed by another.

Glycolysis - Rxn 3 reaction 3: reaction 3: phosphorylation of fructose 6- phosphate. ATP ADP

Glycolysis - Rxn 4 reaction 4: reaction 4: cleavage of fructose 1,6-bisphosphate to two triose phosphates.

Glycolysis - Rxn 5 reaction 5: reaction 5: isomerization of triose phosphates. Catalyzed by phosphotriose isomerase. Reaction involves two successive keto-enol tautomerizations. Only the D enantiomer of glyceraldehyde 3-phosphate is formed.

Glycolysis - Rxn 6 Reaction 6: Reaction 6: oxidation of the -CHO group of D-glyceraldehyde 3-phosphate. The product contains a phosphate ester and a high- energy mixed carboxylic-phosphoric anhydride.

Glycolysis - Rxn 7 Reaction 7: Reaction 7: transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP.

Glycolysis - Rxn 8 & 9 Reaction 8: Reaction 8: isomerization of 3-phosphoglycerate to 2-phosphoglycerate. Reaction 9: Reaction 9: dehydration of 2-phosphoglycerate.

Glycolysis - Rxn 10 Reaction 10 Reaction 10: phosphate transfer to ADP

Glycolysis: SUMMARY: Figure 27.3 Note: Glycer-3 phosphate X 2 2 ATP produced 1 ATP used

Glycolysis: Summary The net equation for glycolysis:

Confirming your knowledge Of the 36 molecules of ATP produced by the complete metabolism of glucose, how many are produced in glycolysis alone? ____ What is the net total ATP production? Total: 36 ATP ___ ATP

Reactions of Pyruvate: Fig 27.4 Pyruvate metabolized three ways: depends on organism & presence/absence of O 2 NOTE: Anaerobic = w/o Oxygen Aerobic = w/ Oxygen

Reactions of Pyruvate A key to understanding the biochemical logic behind two of these reactions of pyruvate is to recognize that glycolysis needs a continuing supply of NAD +. If no oxygen is present to reoxidize NADH to NAD +, then another way must be found to reoxidize it.

Pyruvate to Lactate Under anaerobic (NO Oxygen) conditions, the most important pathway for the regeneration of NAD + is reduction of pyruvate to lactate. Pyruvate, the oxidizing agent, is reduced to lactate.

Pyruvate to Lactate While reduction to lactate allows glycolysis to continue, it increases the concentration of lactate and also of H + in muscle tissue When blood lactate reaches about 0.4 mg/100 mL, muscle tissue becomes almost completely exhausted, esp. b/c H + ions. ((ACID!))

Pyruvate to Ethanol Yeasts and several other organisms regenerate NAD + by this two-step pathway: decarboxylation of pyruvate to acetaldehyde. Acetaldehyde is reduced to ethanol.

Pyruvate to Acetyl-CoA Under aerobic conditions, pyruvate undergoes oxidative decarboxylation. The carboxylate group is converted to CO 2. The remaining two carbons are converted to the acetyl group of acetyl CoA.

Confirming your knowledge The end product of glycolysis (pyruvate) cannot enter as such into the citric acid cycle. What is the name of the process that converts this C3 compound to a C2 compound?

Catabolism of Glycerol Glycerol enters glycolysis via dihydroxyacetone phosphate. 7.3 kcal/mole 3.4 kcal/mole.

Challenge Question Which yields more Energy upon hydrolysis: ATP or glycerol 1- phosphate and Why?

Summary Glycolysis yields 2 net ATP ATP is the molecule of choice for cell(s) Energy ATP is a High E yielding molecule (7.3 kcal/mole) Pyruvate is the END product of Glycolysis » under aerobic conditions  Acetyl CoA  further ATP!!! »under anaerobic conditions  Lactate  (muscle fatigue)