Ch. 13: Glycolysis (WIP)

glycolysis overall

sequence of 10 cytosolic enzyme-catalyzed rxns

2 ‘stages’ of glycolysis

hexose stage (energy investment); triose stage (energy extraction)

hexose stage

energy investment stage; rxns 1 to 5. two phosphorylations using atp; 6C molecule split in to 2 3C molecules

triose stage

energy extraction phase; rxns 6 to 10. each C3 is catabolized to generate 1 NADH & 2 ATP

glycolysis products

2 pyruvate, 2 ATP, 2 NADH, 2H+, 2H2O

where is free energy extracted in glycolysis

through direct phosphorylation and redox rxns

glucokinase/hexokinase

step 1 in glycolysis. an irreversible regulated rxn.

isozyme

multiple forms of an enzyme that catalyze the same chemical reaction but differ in their amino acid sequence and properties; will have different Km values

hexokinse isozymes

4 found in mammals. high Km of hexokinase IV in liver allows it to respond to large increases in blood glucose

glucose-6-phosphate isomerase

glycolysis step 2. glucose-6-phosphate→fructose-6-phosphate

phosphofruktokinase-1 (PFK-1)

glycolysis step 3; second irreversible step. fructose 6 phosphate→fructose 1,6-bisphosphate

what type of rxn does glucose-6-phosphate isomerase catalyze?

aldose → ketose

aldolase

step 4 of glycolysis; cleaves fructose-1,6-bisphosphate into GAP and DHAP

DHAP

dihydroxyacetone phosphate; C1 to C3 of FBP.

GAP

glyceraldehyde 3-phosphate; C4 to C6 of FBP

triose phosphate isomerase

step 5 of glycolysis; interconverts DHAP and GAP. GAP is the desiable substrate for the next step.

glyceraldehyde 3-phosphate dehydrogenase

step 6 of glycolysis and the first energy-harvesting stage. oxidation of GAP coupled to reduction of NAD+. GAP + NAD+ P → 1,3-bisphosphoglycerate (1,3-BPG) + NADH + H

phosphoglycerate kinase

step 7 of glycolysis. 1,3-bisphosphoglycerate + ADP → 3-phosphoglycerate + ADP

phosphoglycerate mutase

step 8 of glycolysis. 3-phosphoglycerate → 2-phosphoglycerate

enolase

step 9 of glycolysis. 2-phosphoglycerate → phosphoenolpyruvate (PEP) + H2O

what type of enzyme is enolase?

a dehydratase; eliminates H2O

PEP

phosphoenolpyruvate; has very high phosphoryl group transfer potential

pyruvate kinase

step 10 of glycolysis. PEP + ADP + H → pyruvate + ATP. the second ATP-producing step and the third metabolically irreversible one.

how is pyruvate kinase regulated?

allosterically and covalently

5 fates of pyruvate

decarboxylation to acetyl-coa; carboxylation to oxaloacetate; reduction to ethanol; reduction to lactate; amination to alanine.

aerobic oxidation of pyruvate

decarboxylated to acetyl-coa, then fully oxidized to CO2 (CAC) and H2O (ETC)