Catabolism of Glucose:Glycolysis Figure 22.3 Glyceraldehyde 3-phosphate Glyceraldehyde 3-phosphate is 0 0P032 (continued) oxidized to a carboxylic acid and -NAD',P then phosphorylated to yield -OH NADH/H+ 1.3-bisphosphoglycerate. CH20P0,2 OH 1,3-Bisphosphoglycerate 03POCH2CHCO2P03 A phosphate is transferred from the carboxyl group to ADP,resulting in synthesis of an ATP and yielding ATP 一OH 3-phosphoglycerate. CH20P02 OH 3-Phosphoglycerate 0POCH2CHCO27 c-0 0 Isomerization of 3-phosphoglycerate gives 2-phosphoglycerate. o 一0P032 CH2OH 0P0 2-Phosphoglycerate HOCH2CHCO2 Dehydration occurs to yield phosphoenolpyruvate(PEP) 0PO32 Phosphoenolpyruvate H2C-CCO2 Aphosphate is transferred from PEP to ADP,yielding pyruvate and ATP. ATP 0 CH3CCO2
Figure 22.3 (continued) Catabolism of Glucose: Glycolysis
Catabolism of Glucose:Glycolysis STEPS 1-2 OF FIGURE 22.3:PHOSPHORYLATION AND ISOMERIZATION Glucose is phosphorylated at the C6 hydroxyl group by reaction with ATP Catalyzed by hexokinase Reaction requires Mg2+as a cofactor to complex with the negatively charged phosphate oxygens Glucose 6-phosphate results Isomerization of glucose 6-phosphate gives fructose 6- phosphate a Catalyzed by glucose 6-phosphate isomerase 1.Initial opening of the glucose hemiacetal ring to the open-chain form 2. Keto-enol tautomerization to a cis enediol,HO-C=C-OH 3.Further tautomerization to a different keto form produces open- chain fructose 4.Cyclization to a hemiacetal completes the process
STEPS 1-2 OF FIGURE 22.3: PHOSPHORYLATION AND ISOMERIZATION Glucose is phosphorylated at the C6 hydroxyl group by reaction with ATP ▪ Catalyzed by hexokinase ▪ Reaction requires Mg2+ as a cofactor to complex with the negatively charged phosphate oxygens ▪ Glucose 6-phosphate results ▪ Isomerization of glucose 6-phosphate gives fructose 6- phosphate ▪ Catalyzed by glucose 6-phosphate isomerase 1. Initial opening of the glucose hemiacetal ring to the open-chain form 2. Keto-enol tautomerization to a cis enediol, HO-C=C-OH 3. Further tautomerization to a different keto form produces openchain fructose 4. Cyclization to a hemiacetal completes the process Catabolism of Glucose: Glycolysis
Catabolism of Glucose:Glycolysis Mechanism of step 2 in glycolysis,the isomerization of glucose 6- phosphate to fructose 6-phosphate OH H -OH 2-03POCH2 HO- -H HO 一H HO H- -OH -OH HO- H 一OH H OH CH20P032 CH2OPO32- a-Glucose Enediol 6-phosphate CH2OH C=0 HO- 一H 2-03POCH2 CH2OH H- OH H -OH CH2OPO32- OH a-Fructose 6-phosphate
Mechanism of step 2 in glycolysis, the isomerization of glucose 6- phosphate to fructose 6-phosphate Catabolism of Glucose: Glycolysis
Catabolism of Glucose:Glycolysis STEP 3 OF FIGURE 22.3:PHOSPHORYLATION Fructose 6-phosphate is converted in step 3 to fructose 1,6- biphosphate(FBP) A phosphofructokinase-catalyzed reaction with ATP Mechanism similar to step 1 Mg2+required as the cofactor Result of step 3 is a molecule ready to be split into the two 3-carbon intermediates 0 0 0 OPOCH2 CH2OH OPOCH2 OH ATP ADP OPOCH2 OH 0 0 HO 0 HO 0 HO CH2OH CH20P032 OH OH OH a-Fructose B-Fructose B-Fructose 6-phosphate 6-phosphate 1,6-bisphosphate(FBP)
STEP 3 OF FIGURE 22.3: PHOSPHORYLATION Fructose 6-phosphate is converted in step 3 to fructose 1,6- biphosphate (FBP) ▪ A phosphofructokinase-catalyzed reaction with ATP ▪ Mechanism similar to step 1 ▪ Mg2+ required as the cofactor ▪ Result of step 3 is a molecule ready to be split into the two 3-carbon intermediates Catabolism of Glucose: Glycolysis
Catabolism of Glucose:Glycolysis STEP 4 OF FIGURE 22.3:CLEAVAGE OF FRUCTOSE 1,6- BISPHOSPHATE Fructose 1,6-bisphosphate is cleaved in step 4 into two 3- carbon pieces: Dihydroxyacetone phosphate (DHAP) Glyceraldehyde 3-phosphate (GAP) C3-C4 bond of fructose 1,6-bisphosphate breaks Cleavage is the reverse of an aldol reaction -Catalyzed by an aldolase
Fructose 1,6-bisphosphate is cleaved in step 4 into two 3- carbon pieces: ▪ Dihydroxyacetone phosphate (DHAP) ▪ Glyceraldehyde 3-phosphate (GAP) ▪ C3-C4 bond of fructose 1,6-bisphosphate breaks ▪ Cleavage is the reverse of an aldol reaction ▪ Catalyzed by an aldolase STEP 4 OF FIGURE 22.3: CLEAVAGE OF FRUCTOSE 1,6- BISPHOSPHATE Catabolism of Glucose: Glycolysis