View
216
Download
3
Category
Preview:
Citation preview
Glycolysis
Glucose utilization in cells of higher plants and animals
GlycolysisWhat is it?10-step metabolic pathwayStarts the breakdown of glucose to get energy
GlycolysisGlycolysis consists of reactions that convert glc to pyruvateUnder aerobic conditions: pyruvate acetyl CoAUnder anaerobic conditions: pyruvate ethanol + CO2 or pyruvate lactate
Glycolysis
Glycolysis
ATP formation coupled to glycolysis
Glucose + 2NAD+ 2pyruvate + 2NADH + 2H+ G˚ = -146 kJ/mol
2ADP + 2Pi 2ATP + 2H2OG˚ = 2 x 30.5 kJ/mol = 61 kJ/mol
Net reaction:Glc + 2NAD+ + 2ADP + 2Pi 2pyr + 2NADH + 2H+ + 2ATP + 2H2O G˚ = -146 kJ/mol + 61 kJ/mol = -85 kJ/mol
After glycolysis, pyruvate goes on to be oxidized completely to CO2 and H2O which has a total standard G˚ = -2840 kJ/mol
Glycolysis
Phosphorylated IntermediatesEach of the 9 intermediates between glc and pyr are phosphorylated
Functions of intermediates
1. Role of charged phosphate
2. Energy storage
Glycolysis - PrepReaction 1 - HexokinaseKinases transfer phosphoryl group from ATP to other molecules
Koelle, lec15, p7
Glc enters cell - how?glc-6-phosphate is not a substrate for transporterHK in all cellsGlucokinase (isozyme of HK) more specific for glc
irreversible
Reaction 2 - Glucose 6-phosphate isomeraseMove carbonyl to carbon 2G˚ = 1.7 kJ/mol (reversible)
Glycolysis - Prep
Reaction 3 - Phosphofructokinase-1Adds another phosphoryl group to sugarRegulatory enzyme, major point of regulation in glycolysisActivity of PFK-1 regulated how?G˚ = -14.2 kJ/mol (irreversible)
Koelle, lec15, p8
Glycolysis - Prep
(PFK-1)
Reaction 4 - AldolaseBreaks the 6-carbon compound into two 3-carbon compoundsAn aldol cleavage (an aldehyde and an alcohol are generated)
G˚ = 23.8 kJ/mol (irreversible or reversible - why??)
Koelle, lec15, p8
Glycolysis - Prep
Reaction 5 - Triose phosphate isomeraseGet two identical 3-carbon unitsNeed glyceraldehyde 3-phosphate to go to next stepEnd of prep phase
G˚ = 7.5 kJ/mol (reversible)
Koelle, lec15, p9
Glycolysis - Prep
Glycolysis - PayoffReaction 6: Glyceraldehyde 3-phosphate dehydrogenaseLoss of 2e- and 2H+
First of 2 energy-conserving rxns that form ATPG˚ = 6.3 kJ/mol (reversible)
Biochemists use “~” to indicate bonds with high phosphoryl group transfer potentials
Principle 3 - few important molecules carry the “currencies” of metabolism, NAD+ = Reducing packet
Koelle, lec15, p10
Glycolysis - PayoffReaction 7: Phosphoglycerate kinase (named for reverse rxn)Harvest the high phosphoryl group transfer potential of 1,3-bisphosphoglycerate to make ATPG˚ = -18.5 kJ/mol
Sum of last 2 rxns (steps 6/7)Glyceraldehyde 3-phosphate + ADP + Pi + NAD+ 3-phosphoglycerate + ATP + NADH + H+
G˚ = -12.5 kJ/mol
Prin. 4 coupled rxns drive energy-requiring processes
Koelle, lec15, p10
Glycolysis - PayoffReaction 8 and 9: Phosphoglycerate mutase and EnolaseRearrange the molecule to produce a form with a high phosphoryl group transfer potential (“~”)Step 8G˚ = 4.4 kJ/molStep 9G˚ = 7.5 kJ/mol
Large differences in free energies of hydrolysis:2-phosphoglycerate -17.6 kJ/mol Phosphoenolpyruvate -61.9 kJ/mol
Glycolysis - PayoffReaction 10: Pyruvate kinaseHarvest the high phosphoryl group transfer potential of PEP to make ATPG˚ = -31.4 kJ/mol (irreversible)
Koelle, lec15, p11
Glycolysis - Enzyme mechanisms1. Same few chemical transformations get used over & overGlycolysis has:
2 isomerases (+ 1 mutase)4 kinasesdehydrogenase
2. Breaking a carbon-carbon bond: aldolase
Koelle, lec15, p14
Glycolysis - Enzyme mechanisms
Glycolysis - Enzyme mechanisms
Koelle, lec15, p15
Glycolysis - Enzyme mechanisms3. Energy coupling: Glyceraldehyde 3-phosphate dehydrogenase
His - general baseCys - nucleophile
Glycolysis - Enzyme mechanisms3. Energy coupling: Glyceraldehyde 3-phosphate dehydrogenase
Koelle, lec15, p16
His - general baseCys - nucleophile
Recommended