Glycolysis Flashcards
Glycolysis net reaction
Glucose + 2 ADP + 2 NAD+ + 2 Pi -> 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
2 stages of glycolysis
Hexose stage
Triose stage
Differences in ATP usage between hexose stage and triose stage
Hexose stage consumes ATP, but triose stage regenerates more ATP than what was consumed
Step 1 of glycolysis
Transfer of phosphoryl group from ATP to glucose
Takes place at primary alcohol (most nucleophilic)
Glucose -> glucose 6-phosphate
Enzymes: hexokinase and glucokinase
Isoforms
Different structures of an enzyme that have the same function
Step 2 of glycolysis
Isomerization: aldose to ketose (proceeds through open-chain form that is generated within the enzyme active site)
Glucose 6-phosphate -> fructose 6-phosphate
Enzyme: glucose 6-phosphate isomerase
Stereospecificity of step 2
Highly stereospecific: C-2 epimer isn’t formed
Step 3 of glycolysis
Transfer of a 2nd phosphoryl group from ATP to fructose 6-phosphate
Fructose 6-phosphate -> fructose 1,6-bisphosphate
Enzyme: phosphofructokinase-1
Anomeric form of fructose 6-phosphate that phosphofructokinase-1 prefers
Beta form
Alpha anomer from step 3 must undergo conformational change
First committed step of glycolysis
Step 3
Step 4 of glycolysis
C3-C4 bond cleavage, yielding 2 triose phosphates
Fructose 1,6-bisphosphate -> dihydroxyacetone phosphate and glyceraldehyde 3-phosphate
Eznyme: aldolase
Portions of fructose 1,6-bisphosphate that DHAP and G3P are derived from
DHAP is derived from C1 to C3 of fructose
G3P is derived from C4 to C6 of fructose
Step 5 of glycolysis
Rapid interconversion of triose phosphates
DHAP -> G3P
Enzyme: triose phosphate isomerase
Step 6 of glycolysis
Oxidation and phosphorylation, yielding a high-energy mixed-acid anhydride
G3P -> 1,3-bisphosphoglycerate
Enzyme: glyceraldehyde 3-phosphate dehydrogenase
Redox reaction in step 6
Generation of H+ (NAD+ -> NADH + H+)
Step 7 of glycolysis
Transfer of a high-energy phosphoryl group to ADP, yielding ATP
1,3-bisphosphoglycerate -> 3-phosphoglycerate
Enzyme: phosphoglycerate kinase
First ATP-generating step of glycolysis
Step 7
Substrate level phosphorylation
Molecule directly transfers phosphoryl group to ADP
Step 8 of glycolysis
Intramolecular phosphoryl group transfer
3-phosphoglycerate -> 2-phosphoglycerate
Enzyme: phosphoglycerate mutase
Mutases
Class of isomerase that catalyze transfer of a phosphoryl group from 1 part of a molecule to another
Mutase mechanism
Enzyme phosphoryl intermediate: phosphoryl group is transferred to enzyme and then transferred back to substrate
Step 9 of glycolysis
Dehydration to an energy-rich enol ester
2-phosphoglycerate -> phosphoenolpyruvate
Enzyme: enolase
Step 10 of glycolysis
Transfer of a high-energy phosphoryl group to ADP, yielding ATP
Phosphoenolpyruvate -> pyruvate
Enzyme: pyruvate kinase
Metabolically irreversible steps of glycolysis
Step 1 (glucose -> glucose 6-phosphate) Step 3 (fructose 6-phosphate -> fructose 1,6-bisphosphate) Step 7 (1,3-bisphosphoglycerate -> 3-phosphoglycerate) Step 10 (phosphoenolpyruvate -> pyruvate)
Metabolism of pyruvate to ethanol: what it achieves
Survival mechanism of some organisms in long-term anaerobic conditions
Regenerates NAD+ needed for modest energy production
2 reactions of pyruvate to ethanol
- Decarboxylation of pyruvate to acetaldehyde (pyruvate decarboxylase)
- Reduction of acetaldehyde to ethanol (alcohol dehydrogenase)
Reduction of pyruvate to lactate
Lactate dehydrogenase (NADH cofactor) reduces pyruvate to L-lactate
Short-term anaerobic conditions: regeneration of NAD+ in the absence of oxygen
Lactic acid is eventually moved from the muscles to the liver to be converted back to pyruvate
Free energy equation
delta G= delta G0 + RTln(Q)
Q= current reaction quotient
Glycolysis using fructose
Fructose is converted into 2 G3P: 2 ATP are invested
Glycolysis using galactose
Galactose is converted into glucose 1-phosphate through UDP-glucose (galactose is traded for glucose)
Glycolysis using mannose
Mannose is converted into fructose 6-phosphate (aldose -> ketose)
