Biochem ch2
Page 1: Introduction
Anaerobic Metabolism of Carbohydrates in the Red Blood Cell.
Page 2: Glycolysis Overview
Glycolysis is the central pathway for glucose metabolism in all cells.
Glucose is the major carbohydrate, serving as the backbone and monomer unit of cellulose and starch.
It is the only fuel used by all cells, including intestinal microbes, initiating glucose metabolism through glycolysis (carbohydrate splitting).
Glycolysis is catalyzed by soluble cytosolic enzymes.
The erythrocyte (red blood cell) uniquely relies on glucose and glycolysis as its sole energy source.
Page 3: Products of Glycolysis
Pyruvate, a three-carbon carboxylic acid, is produced as the end product of anaerobic glycolysis (2 moles of pyruvate per mole of glucose).
In cells with mitochondria, pyruvate converts to CO2 and H2O (aerobic glycolysis).
In RBCs, pyruvate is reduced to lactic acid due to the lack of mitochondria.
Each mole of glucose yields 2 moles of lactate, which are excreted into the blood; they contain the same number of carbons, hydrogens, and oxygens as glucose.
Free energy from glucose cleavage produces 2 moles of ATP per mole of glucose converted into lactate.
RBC uses ATP primarily to maintain electrochemical and ion gradients across the plasma membrane.
Page 4: Key Metabolites in Glycolysis
HO, ADP, Pi structure diagrams highlight biochemical compounds involved.
D-Glucose (C6H12O6) and L-Lactate (C3H6O3) structures are relevant.
Page 5: 2,3-BPG and the Pentose Phosphate Pathway
10%-20% of glycolytic intermediate 1,3-bisphosphoglycerate is diverted to synthesize 2,3-bisphosphoglycerate (2,3-BPG), which regulates O2 affinity of hemoglobin.
The pentose phosphate pathway accounts for ~10% of glucose metabolism in RBC, protecting against oxidative stress.
Page 6: Erythrocyte Metabolism
RBC relies exclusively on blood glucose as a metabolic fuel and comprises 40%-45% of blood volume.
RBC is structurally and metabolically simple, having lost organelles during maturation, thus lacking nuclei.
Page 7: Protein Synthesis and Fuel Sources
Without ribosomes, RBC cannot synthesize protein or oxidize fats requiring mitochondria.
Dietary sugars (fructose, galactose) convert to glucose mainly in the liver.
RBC metabolism of glucose is wholly anaerobic due to its role in oxygen transport.
Page 8: Glycolysis Introduction
Overview and significance of glycolysis.
Page 9: Glycolytic Process
Glucose enters the RBC by facilitated diffusion via GLUT-1.
Glycolysis starts with glucose phosphorylation into glucose-6-phosphate (Glc-6-P), involving 10 enzymatic steps.
ATP is expended in investment stage to form fructose-1,6-bisphosphate (Fru-1,6-BP).
Page 10: ATP Production Yield
Glycolysis converts triose phosphates into lactate, producing four ATP but yielding a net gain of 2 moles of ATP per glucose, representing a low energy extraction efficiency compared to mitochondrial processes.
Page 11: Interconnected Pathways
Glycolysis has 10 steps to convert glucose to lactate, allowing glycolytic intermediates to link into other metabolic pathways (fats, proteins, nucleic acids).
Page 12: Metabolic Branch Points
Intermediates linking glycolysis with other pathways (glycogen, sugars, ribose for nucleotides).
Page 13: Glucose-6-phosphate Entry
GLUT-1 transporter facilitates glucose uptake.
Phosphorylation of glucose to Glc-6-P by hexokinase is the commitment step, trapping glucose inside RBC.
Page 14: Conversion to Fru-6-P
Conversion of Glc-6-P to fructose-6-phosphate by phosphoglucose isomerase.
Further phosphorylation of Fru-6-P by phosphofructokinase-1 (PFK-1) investing another ATP.
Page 15: Glycolytic Enzyme Reaction Summary
Detailed representation of enzymatic reactions involving hexokinase, phosphoglucose isomerase, and PFK-1.
Page 16: Commitment to Glycolysis
Fru-1,6-BP is a crucial intermediate regulating entry into glycolysis, catalyzed by PFK-1 with irreversible action.
Page 17: Aldolase Reaction
Aldolase yields two triose phosphates from Fru-1,6-BP, continuing glycolysis.
Glyceraldehyde-3-phosphate proceeds through the yield stage while dihydroxyacetone phosphate interconverts for complete metabolism.
Page 18: Yield Stage Details
The yield stage of glycolysis produces 4 ATP per 2 triose phosphates and nets 2 ATP per glucose.
Page 19: Substrate-Level Phosphorylation
High-energy phosphate transfer from acyl phosphate compound (1,3-BPG) to ADP to form ATP in substrate-level phosphorylation.
Page 20: GAPDH and ATP Generation
The oxidizing reaction of glyceraldehyde-3-phosphate catalyzed by GAPDH traps phosphate, regenerating NAD+ and forming high-energy 1,3-BPG.
Page 21: Substrate-Level Phosphorylation Reaction Overview
Enzymatic steps that convert 1,3-BPG to ATP.
Page 22: Further Phosphorylation Steps
The conversion of 2-phosphoglycerate to phosphoenolpyruvate (PEP) involves dehydration reactions leading to ATP production.
Page 23: ATP Generation Mechanism
Substrate-level phosphorylation yields ATP via glycolytic enzymes including PGK and PK.
Page 24: Pyruvate Formation
The process involved in forming pyruvate and generating the second ATP via substrate-level phosphorylation.
Page 25: Glycolytic ATP Summary
Total ATP production analysis reveals a net yield of 2 moles of ATP.
Page 26: Regeneration of NAD+
LDH regenerates NAD+ by converting pyruvate to lactate, allowing continued anaerobic glycolysis.
Page 27: Anaerobic vs Aerobic Conditions
LDH activity under anaerobic conditions yields lactate while aerobic conditions lead to CO2 and H2O by mitochondria, with lactate forming under hypoxic conditions.
Page 28: Fermentation Processes
Fermentation, the anaerobic metabolism term, varies among organisms: bacteria, yeast converting pyruvate to lactate or ethanol.
Page 29: Yeast Fermentation Steps
Decarboxylation of pyruvate followed by ethanol production in yeast.
Page 30: Nutritional Aspects of Fermentation
Alcohol yields energy between carbohydrates and lipids and contributes to numerous fermented food products.
Page 31: Gut Microbiota and Fermentation
Role of anaerobic bacteria in digestion and immune protection, influenced by dietary composition.
Page 32: Glycolytic Regulation
Overview of regulation mechanisms in glycolysis.
Page 33: Allosteric Regulation in RBCs
Glycolysis is regulated at three critical enzyme steps, aligning with the energy requirements of the RBC.
Page 34: Hexokinase Regulation Mechanism
Hexokinase activity Feedback inhibition by its product, glucose-6-phosphate (Glc-6-P).
Page 35: Primary Regulation by PFK-1
PFK-1 is the main regulatory step influenced by ATP and AMP concentrations in glycolysis.
Page 36: ATP's Dual Role
ATP acts as both a substrate and an allosteric inhibitor of PFK-1, allowing tight regulation.
Page 37: AMP Activation
The concentration difference between ATP and AMP regulates PFK-1 activity, enhancing glycolysis during higher energy demand.
Page 38: Energy Status Sensitivity
PFK-1 activity correlates with the (AMP + ADP)/ATP ratio, modulating glycolytic rate.
Page 39: Glycolytic Regulation Feedback Loop
Feedback mechanisms adapt glycolytic rates during varying energy states.
Page 40: Pyruvate Kinase Activation
Pyruvate kinase is allosterically activated by Fru-1,6-BP, preventing triose phosphate accumulation.
Page 41: Characteristics of Regulatory Enzymes
Features of regulatory enzymes: responsiveness, low Vmax, and catalyzing irreversible reactions.
Page 42: Complex Regulation in Other Tissues
Glycolysis regulation is more intricate in tissues other than RBC due to variable fuel consumption and metabolic flexibility.
Page 43: Regulation Summary Table
Summary of glycolytic enzyme regulation in the red cell, detailing inhibition and activation mechanisms.
Page 44: Pentose Phosphate Pathway Overview
Overview of the pathway designed for nucleotide synthesis and interaction with glycolysis.
Page 45: Shunting and Recycling in the Pathway
The pentose phosphate pathway acts as a shunt, converting pentoses back to glycolytic intermediates as needed.
Page 46: NADPH Generation in the Pathway
NADPH's primary role in lipid biosynthesis and detoxification highlighted, especially in the liver and RBC.
Page 47: Mechanisms of NADPH Production
NADPH produced through specific enzymatic reactions in pentose phosphate pathway.
Page 48: Enzyme Usage Difference
Distinction between NAD(H) use in glycolytic enzymes and NADP(H) in pentose phosphate pathway.
Page 49: NADPH Production Reaction Diagram
Visual representation of NADPH-producing reactions in the pentose phosphate pathway.
Page 50: Interconversion of Five-Carbon Sugars
Conversion processes of ribulose-5-phosphate back into glycolytic intermediates for nucleic acid synthesis in active cells.
Page 51: Summary of Equilibrium Reactions
Enumeration of equilibrium reactions that recycle pentose phosphates into glycolytic intermediates.
Page 52: Equilibrium Reaction Table
Table summarizing substrates and products of equilibrium reactions within the pentose phosphate pathway.
Page 53: Glucose Shunting in RBC
Emphasizes temporary diversion of glucose in pentose phosphate pathway with focus on continued glycolytic activity.
Page 54: GSH and Oxidative Protection
Glutathione's role as an antioxidant, necessitating NADPH for its reduced form maintenance.
Page 55: GSH Chemical Structure
Structure and relevance of GSH in cellular function and protection mechanisms.
Page 56: Glutathione Reactions
Role of glutathione reductase and peroxidase in detoxification processes, with visual representation.
Page 57: Glutathione Functions Overview
Protective roles of GSH in the cell's oxidative defense extending to protein stabilization.
Page 58: GSH Protein Interaction
GSH's function in maintaining protein thiol groups in reduced states, preventing oxidative crosslinking.
Page 59: References
Links to additional video resources relating to the anaerobic metabolism of carbohydrates in red blood cells.