glycolysis: energy generation without an oxygen requirement glucose biofuel prominence: low-reactive...
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Glycolysis: Energy Generation Without an Oxygen Requirement
Glucose Biofuel Prominence:
Low-reactive ring-form minimizes protein glycosylation
Glycolysis: A Three Step Process
• Glucose trapping and destabilization (priming)
•Three carbon unit generation (cleaving)
• Energy generation
Induced Fit in Hexokinase
Glucose induces a large enzyme conformational change
Substrate-induced cleft closing prevents ATP hydrolysis
Kinases require a divalent metal ion
What function does Mg+2 play in hexokinase?
Hexokinase Closed Around Substrates
What mechanisms of catalysis are operative?
Hexokinase Reaction Mechanism
What is the Nu:, electrophile, and leaving group in this reaction?
Phosphoglucose Isomerase: Aldose to Ketose Conversion
PGI Reaction Mechanism
Phosphoglucose Isomerase (PGI) G6P Conversion via Acid-Base Catalysis
Base catalyzed bond formation
Phosphoglucose Isomerase (PGI) G6P Conversion via Acid-Base Catalysis
Acid catalyzedketal formation
Phosphoglucose Isomerase (PGI) G6P Conversion via Acid-Base Catalysis
H+
Base catalyzes ring closure
Phosphoglucose Isomerase (PGI) G6P Conversion via Acid-Base Catalysis
Phosphofructokinase: Trapping the Fructose Isomer
What is the mechanism for this reaction?
Glycolysis Stage I: Glucose Trapping and Destabilization (priming)
Six Carbon Sugar Cleaved to Two Three Carbon Units
What is the bond to be cleaved?
Which alcohol becomes an aldehyde?
Haworth and Fischer Projections Equivalency
The functional group that is down in a Haworth projection is positioned how in a Fischer structure?
Aldolase
Fructose-1,6-bisphosphate binds to the aldolase enzyme for covalent catalysis
Aldolase Reaction Mechanism
Aldolase Reaction Mechanism
What is lost when the Schiff base forms?
Aldolase Rxn Mechanism
Aldolase Reaction Mechanism
Compare and contrast a Schiff base with a carbonyl group.
Aldolase Reaction Mechanism
What is the process for Schiff base to carbonyl conversion?
H2O
Aldolase cleaves FBP into GAP and DHAP
Aldolase Reaction Mechanism
Which previous glycolytic step is similar to TIM?
Reversible and driven towards GAP due to product depletion
Triose Phosphate Isomerase (TIM)
Glycolysis: Step #5Triose Phosphate Isomerase
DHAP conversion to GAP necessary to proceed through glycolysis
Triose Phosphate Isomerase Reaction Mechanism
TIM- or α,β-barrel with 8 parallel β-strands surrounded by 8 α-helices.
Two ATPs are initially invested.
One glucose is metabolized into two GAP molecules.
Stoichiometry: Stages 1-2 of Glycolysis
Road Map for Energy Harvest (Stage 3)
Glyceraldehyde-3-Phosphate Dehydrogenase: Covalent Catalysis
Glyceraldehyde-3-Phosphate Dehydrogenase: a 2 Step Process
What amino acid will serve as a nucleophile to form a thioester?
Glyceraldehyde-3-Phosphate Dehydrogenase: Reaction Mechanism
Glyceraldehyde-3-Phosphate Dehydrogenase: Catalysis Energetics
Actual coupled reaction
Hypothetical reaction with no coupling
What is the Nu:, electrophile and leaving group for this reaction? (hint: consider hexokinase in reverse)
Phosphoglycerate Kinase
Glycolysis: the Three Final Steps
Pyruvate Kinase
What is the Nu:, electrophile and leaving group for this reaction? (hint: consider phosphoglycerate kinase)
∆G°ʹ ∆GEnzyme (kcal/mol) (kcal/mol)
1near equilibrium means that ∆G is about zero
What is the relationship between ∆G and ∆G°ʹ?When can ∆G and ∆G°ʹ diverge?
Glycolysis Energetic
• Water represents metabolite flux
• Water amount in flask represents intermediate abundance
• Flasks connections are enzymes
• Vertical drop represents decrease in free energy
ΔG° = height difference between flask bottomsΔG = height difference between water levels
Regulating Glycolysis: A Pictorial Analogue
Metabolic Regulation
Irreversible reactions are potential regulatory sites (e.g. hexokinase, phosphofructokinase and pyruvate kinase)
What duel role does ATP play in PFK-1 catalysis?
In what direction does ATP regulate phosphofructokinase?
Energy Status Regulates Glycolytic Flow
Elevated [ATP] sufficient energy; elevate [AMP] low energy
ADP + ADP ↔ ATP + AMP <adenylate kinase>
Muscle Tissue
Fructose-2,6-Bisphosphate an Allosteric Regulator of Phosphofructokinase-1
F-2,6-BP amplifies or diminishes PFK-1 activity?
PFK-2
Liver Tissue
Front activation by fructose-6P
Fructose-2,6-Bisphosphate Reduces ATP Inhibition of Phosphofructokinase-1
ATP is a substrate and inhibitor of PFK-1
PFK-2
Liver Tissue
Fructose Entry Points for Glycolysis
Glucose + Fructose
Major dietary sugars: sucrose (table sugar) and fructose (high-fructose corn syrup)
Glycerol-3P
Fructose Metabolism
How is this different than glucose metabolism?
Lipid Synthesis
Fructose Metabolism
Glycerol 3-phosphate a precursor to triacylglycerol
Fructose catabolism bypasses phosphofructokinase regulation
Alternative Fates for Pyruvate
Anaerobic Recycling of NADH for Glycolysis
Microbial Recycling of NADH for Glycolysis
Pyruvate Dehydrogenase:
the Bridge between
Glycolysis and Citric Acid Cycle
Standard Free Energy Change Comparisons for Glucose Catabolism With and Without Oxygen
Pathogenic Obligate Anaerobes
Pyruvate Targeted for Anabolism
The biotin prosthetic group serves as a CO2 carrier
What reaction links biotin to the protein?
Pyruvate Carboxylase: an
Endergonic Reaction
Oxaloacetate
Glucose Metabolism: Both Catabolic and Anabolic
Glucose Metabolism: Both Catabolic and Anabolic
Problems: 1, 3, 5, 7, 13, and 21