Regulation of Glycolysis | Glendale Community College

University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2022
Views:

428

Pages:

11
Author:

erowuot

Chapter 8 Carbohydrate Metabolism Overview Metabolism - catabolic pathways that degrade organic molecules and release energy Carbohydrate metabolism – central role as energy source for life processes Glycolysis – first step in glucose metabolism ¨ Citric acid cycle – cycle of reactions catalyzed by enzymes converting pyruvate to CO2 & water to produce energy (ATP) ¨ Electron transport chain – electrons pass from one compound to another via redox reactions coupled with proton gradient creation ¨ Oxidative phosphorylation – formation of ATP ¨ Chapter 8: Overview §Energy transforming pathways , , , gluconeogenesis, pentose phosphate pathway Figure 8.2 Major Pathways in Carbohydrate Metabolism Section 8.1: Glycolysis Figure 8.2 Major Pathways in Carbohydrate Metabolism §Anaerobic process occurs in almost every living cell §Glucose converted to fructose-1,6-bisphosphate producing two pyruvates §Ten reactions in 2 stages: §Energy investment – 2 ATPs consumed creating substrates for oxidation §Energy producing – 4 ATP & 2 NADH produced §Catabolic process producing net 2 ATP and 2 NADH §Summary equation: Glucose + ADP + 2Pi + 2NAD+ à 2pyruvate + 2ATP + 2NADH + 2H+ + 2H2O Section 8.1: Reactions of the Glycolytic Pathway 1. Synthesis of glucose-6-phosphate §Phosphorylation of glucose §Prevents export out of cell §Facilities binding to active site 2. Conversion of glucose-6-phosphate to fructose-6-phosphate Hexokinase Mg2+ Phosphoglucose isomerase §Conversion of aldose to ketose 3. Phosphorylation of fructose-6phosphate §Irreversible, first committed step Phosphofructokinase-1 (PKF-1) Mg2+ 4. Cleavage of fructose-1,6bisphosphate §Aldol cleavage 5. Interconversion DHAP–G-3-P Triose phosphate isomerase Section 8.1: Reactions of the Glycolytic Pathway 6. Oxidation of glyceraldehyde-3phosphate §Creates high-energy bond; NADH G-3-P dehydrogenase 7. Phosphoryl group transfer §Production of ATP - substratelevel phosphorylation 8. 3-phosphoglycerate ß à 2-phosphoglycerate Phosphoglycerate Kinase Mg2+ Phosphoglycerate mutase 9. Dehydration glycerate-2-phosphate §Formation of PEP Enolase 10. Synthesis of Pyruvate Net production: 2 ATP, 2 NADH, and 2 pyruvate Pyruvate kinase Mg2+ Section 8.1: Fates of Pyruvate Figure 8.7 The Fates of Pyruvate §Aerobic conditions –converted to acetyl-CoA §Enters citric acid cycle forming CO2, NADH, FADH2 §Amphibolic pathway – functions in both anabolic/catabolic processes §Electron Transport System – transfers electrons from NADH/FADH2 to O2 Section 8.1: Fates of Pyruvate Figure 8.7 The Fates of Pyruvate §Anaerobic conditions – impedes oxidation §Homolactic fermentation – reduces to organic compound §Regenerates NAD+ for glycolysis Section 8.1: Fates of Pyruvate Figure 8.7 The Fates of Pyruvate §Anaerobic conditions – impedes oxidation §Alcoholic fermentation – produces ethanol, regenerates NAD+ §Used to make alcoholic beverages Section 8.1: Glycolysis § Three reactions – negative free energy § Hexokinase § Phosphofructokinase § Pyruvate kinase § Essentially irreversible § Sites of allosteric control Section 8.1: Regulation of Glycolysis §Hexokinases I, II, and III §High affinity for glucose §Inhibited by glucose-6-phosphate §Hexokinase IV (Glucokinase) found in liver §Requires higher glucose concentrations §Not inhibited by glucose-6-phosphate §Diverts glucose to storage as glycogen Section 8.1: Regulation of Glycolysis §Phosphofructokinase-1 §Inhibited by citrate, ATP §Fructose-2,6-bisphosphate, produced via hormone- induced covalent modification of PFK-2, activates PFK-1 §Accumulation of fructose-1,6-bisphosphate provides a feed-forward mechanism §Pyruvate kinase §Accumulated fructose-1,6-bisphosphate activates §High AMP concentrations activate §Inhibited by Acetyl-CoA, ATP