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Chapter 11: GlycolysisChapter 11: Glycolysis
“Enjoy the chemical elegance of metabolism”
amylose sucrose lactose glucose fructose
-oseamylase
-ase disaccharides
Active transport passive transport
Low [Glc] High [Glc] Low [Glc]
Chapter 11: GlycolysisChapter 11: Glycolysis
Net Reaction:Glucose + 2 ADP + 2 NAD+ + 2 Pi 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
1-4 = hexose (6C) stage: 2 ATP’s consumed.5-10 = triose 2(3C) stage: 4 ATP’s produced. Net: 2 ATP’s.
Defined: Glucose is converted anaerobically to the three carbon acid pyruvate (only top half diagram)
Max energy when pyruvate from glycolysis enters Citric Acid Cycle Makes reducing eqivalents NADH and QH2 (FADH2)
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Fructose-1,6-bisphosphate
Dihydroxyacetone phosphate
Glyceraldehyde-3-phosphate
1,3-bisphosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
phosphoenolpyruvate
pyruvate
Glyceraldehyde-3-phosphate
1,3-bisphosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
phosphoenolpyruvate
pyruvate
Hexokinase
Glucose-6-phosphate isomerase
Phosphofructokinase-1
Trios phosphate isomerase
Aldolase
Glyceraldehyde-3-phosphate dehydrogenase
Phosphoglycerate kinase
Phosphoglycerate mutase
Enolase
Pyruvate kinase
ATP
ADP
ATP
ADP
ADP
ATPADP
ATP
ADP
ATPADP
ATP
NADH + H+
NAD+ + Pi
NADH + H+
NAD+ + Pi
H2O H2O
Phosphorylation
Phosphorylation
Substrate Level Phosphorylation
Substrate Level Phosphorylation
Oxidation and Phosphorylation
Isomerization
Cleavage
Isomerization
Rearrangement
Dehydration
The Pathway
Glycolysis: Step 1, HexokinaseGlycolysis: Step 1, Hexokinase
Can’t leave the cell
I-III IV
Isozymes Different inhibition profiles Location, Km Control point
C-6
Glycolysis: Step 2Glycolysis: Step 2Glucose 6-Phosphate IsomeraseGlucose 6-Phosphate Isomerase
Stereospecific: uses -Glc; produces -D-fructose-6-phosphate
Opens the chainduring the rxn
Aldose
Ketose
CH2OH
OH
Step 3, Phosphofructokinase-1Step 3, Phosphofructokinase-1
Metabolically irreversible rxn. It is an allosteric enzyme and a REGULATory CONTROL step for glycolysis (AMP and citrate).
PFK-1
First COMMITted step of glycolysis
Phosphofructokinase-1
Other 6-C sugars can enter and convert to fru-6-phos fructose, mannose, etc.
-anomer
Glycolysis: Steps 2 and 3Glycolysis: Steps 2 and 3
Stereospecific: uses -Glc; produces 100% -D-fructose-6-phosphate
Opens the chainduring the rxn
PFK-1
utilizes 100% -anomer
36% -fructose 64% -fructose
CH2OH
OH
Glycolysis: Step 4, AldolaseGlycolysis: Step 4, Aldolase
123
456
Rxn is near equilibrium, so not a control pointBasic residue or metal withdraws an
e- polarizing C2 carbonyl
Basic residue removes a proton from the C4 hydroxyl group
Rapid depletion of 2 products in subsequent steps drives rxn
Fig 11.5 Mech
Step 5, Triose Phosphate IsomeraseStep 5, Triose Phosphate Isomerase
Only G3P, not DHAP, can be utilized in step 6 Now have 2 molecules G3P for step 6
Consumption in step 6 maintains steady state conc. of G3P
Ketose-aldose conversion is diffusion controlled
After conversion, C-1=C-6, C-2=C-5, C-3=C4 (see textbook)
near equil.
AldoseKetose
Step 5, Triose Phosphate IsomeraseStep 5, Triose Phosphate Isomerase
near equil.
AldoseKetose
Glycolysis: Step 6Glycolysis: Step 6Glyceraldehyde 3-Phosphate DehydrogenaseGlyceraldehyde 3-Phosphate Dehydrogenase
Oxidation has neg G, some energy conserved in acid anhydride linkage
Oxidation is coupled to phosphorylation to conserve energy, instead of oxidation to free carbonic acid and energy loss
Higher group transfer potential than ATP
from Pi
Step 7, Phosphoglycerate KinaseStep 7, Phosphoglycerate Kinase
Near equilibrium rxn. Reversibility is important for reverse step in glucose synthesis (gluconeogenesis).
Really steps 6&7 couple oxidation to phosphorylation of ADP
Substrate level phosphorylation- Nucleotide diphosphate phosphorylated Donor is not a nucleotide
First ATP generating step
Glycolysis: Step 8, Phosphoglycerate Glycolysis: Step 8, Phosphoglycerate MutaseMutase
iPGM-cofactor independant
dPGM-cofactor dependant
Step 9, EnolaseStep 9, Enolase
phosphomonoester
Enol-phosphate ester
PEP: Very high P-group transferpotential
Glycolysis: Step 10, Pyruvate KinaseGlycolysis: Step 10, Pyruvate Kinase
2nd sub level phosphorylation
3rd metabolically irreverible rxn
Reg allosteric and covalent modification
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Fructose-1,6-bisphosphate
Dihydroxyacetone phosphate
Glyceraldehyde-3-phosphate
1,3-bisphosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
phosphoenolpyruvate
pyruvate
Glyceraldehyde-3-phosphate
1,3-bisphosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
phosphoenolpyruvate
pyruvate
Hexokinase
Glucose-6-phosphate isomerase
Phosphofructokinase-1
Trios phosphate isomerase
Aldolase
Glyceraldehyde-3-phosphate dehydrogenase
Phosphoglycerate kinase
Phosphoglycerate mutase
Enolase
Pyruvate kinase
ATP
ADP
ATP
ADP
ATP
ADP
ATP
ADP
ATP
ADP
ATP
ADP
NADH + H+
NAD+ + Pi
NADH + H+
NAD+ + Pi
H2O H2O
Phosphorylation
Phosphorylation
Substrate Level Phosphorylation
Substrate Level Phosphorylation
Oxidation and Phosphorylation
Isomerization
Cleavage
Isomerization
Rearrangement
Dehydration
Three Metabolically Irreversible Reactions
#3
#10
#1
Most are near equilibrium
Energetics of GlycolysisEnergetics of Glycolysis
**** **
1. Hexokinase3. Phosphofructokinase 110. Pyruvate Kinase
Few large -G steps, irreversible, regulated
Most are near equilibrium and have G close to zero
Steps 2, 4, 5, 6, 7, 8, 9
Enter the Le Chatelier
Physiological Regulation of GlycolysisPhysiological Regulation of Glycolysis
Insulin Independent UptakeBrainLiverRed Blood Cells
Insulin Dependent UptakeMuscleAdipose
Hormones InvolvedHigh blood [Glc], insulin releasedLow blood [Glc], glucagon released
Regulation of Glycolysis by Cellular ImportRegulation of Glycolysis by Cellular Import
[Glucose] high in bloodsteam and low inside most cells- passive transport
High Insulin hormone and [Glc] stimulate increased rate of glucose intake
Insulin binds receptor, GLUT4 hexose transporter able to bind cell surface
Hexose Transporters transport glucose into cells in an insulin dependent manner
ExceptionsSmall intestine
Kidney
Which cell typesare affected?
Enzymatic Regulation of GlycolysisEnzymatic Regulation of Glycolysis
CAC intermediates, slow down, there is already adequatesupply of energy
Regulation network samples the condition of the cytoplasm and applies Principles of Supply and Demand
Not moving forward, stop converting ATP
Cellular rxns are converting ATP and ADP, make more ATP
You’ve committed!Bi-phosphated furanoses, keep pathway moving
Glycolysis: Hexokinase IsozymesGlycolysis: Hexokinase Isozymes
Can’t leave the cell with negative charge
I-III IV
Isozymes Different inhibition profiles Location, Km Control point
Hexokinases (I-III)-regulated negatively by Glc-6-P-if later steps slow down, Glc-6P builds up
Glucokinase (IV) in Liver-regulated negatively by Fru-6-P-pulls glucose out of bloodstream until equil-liver can produce more Glc-6-P-converts Glucose to Glycogen storage
Regulation of Phosphofructokinase-1Regulation of Phosphofructokinase-1
Citrate - feedback inhibitor - regulates supply of pyruvate - links Glycolysis and CAC
Fru-2,6-bisphosphate - strong activator - produced by PFK-2 when excess fru-6-phosphate - indirect means of substrate stimulation or feed forward activation
ATP - product of pathway - allosteric inhibitor
AMP - allosteric activator - relieves inhibition by ATP
Large oligomeric enzyme bacteria/mammals - tetramer yeast - octamer
Regulation of Pyruvate KinaseRegulation of Pyruvate Kinase
High blood [Glc]
Allosteric (feed-forward) activation Fructose-1,6-bisphosphate -allosterically activates -produced in step three -links control steps together
+ F 1,6 BP
Inactivation by covalent modification -blood [Glc] drops, glucagon released -liver protein kinase A (PKA) turned on -PKA phosphorylates pyruvate kinase
Allosteric inhibition by ATP -product of pathway and CAC
Low blood [Glc]