EHS 385_Bioenergetics II_glycolysis_s25 cfs
Page 1: Glycolysis Overview
Steps in Glycolysis
Phosphorylation of Glucose
Glucose is phosphorylated by ATP, resulting in an activated glucose molecule.
Formation of Fructose-1,6-bisphosphate
Rearrangement and a second phosphorylation of glucose yield fructose-1,6-bisphosphate.
Cleavage of the 6-Carbon Molecule
The 6-carbon molecule is split into two 3-carbon G3P (glyceraldehyde-3-phosphate) molecules.
Oxidation and Phosphorylation
Conversion of G3P into 1,3-bisphosphoglycerate (BPG) produces 2 NADH and 2 high-energy BPG molecules.
ATP Production
Removal of phosphate groups generates 2 ATP molecules from ADP, resulting in 2 3-phosphoglycerate (3PG) molecules.
Formation of Phosphoenolpyruvate (PEP)
Dehydration of 3PG results in the creation of 2 high-energy PEP molecules.
Second ATP Production
Conversion of PEP to pyruvate results in the production of 2 more ATP molecules.
End Product
The final product, pyruvate, can enter the mitochondria for further processing if oxygen is available.
Energy Yield
Net gain is 2 ATP from the glycolytic process.
Page 2: Glycolysis Function
Definition: Glycolysis involves the breakdown of carbohydrates (glucose or glycogen) to resynthesize ATP.
Duration: Fuels physical activity for about 90 seconds to 3 minutes.
Types: Can be aerobic (slow) or anaerobic (fast).
Location: Occurs in the sarcoplasm of muscle cells.
Net Gain: Produces a net gain of two ATP and two pyruvate or lactate molecules.
Page 3: Phases of Glycolysis
Two Main Phases
Energy Investment Phase
Requires ATP to form sugar phosphates; is essential to prime the process.
Priming costs 2 ATP if starting with glucose and only 1 ATP with glycogen.
Net Gain: 2 ATP using glucose, 3 ATP using glycogen.
Page 4: Glycolysis Outcomes
End Products: Breakdown of glucose or glycogen produces pyruvate or lactate.
Pyruvate Fate
Anaerobic Pathway:
Pyruvate converts to lactate; faster ATP production but limited duration.
Aerobic Pathway:
Pyruvate enters the Krebs cycle for slower, sustained ATP production.
Page 5: Fast Glycolysis and Lactate
Lactate Formation
Conversion of pyruvate to lactate is catalyzed by lactate dehydrogenase; this process does not produce lactic acid directly, which is a common misconception.
Lactate Role: Transported to the liver for processing (Cori Cycle) to generate glucose, which can provide further energy.
Glycolytic Power: Can fuel intense activities for up to 120 seconds; however, longer durations at high intensity are limited due to glycogen stores.
Page 6: Anaerobic ATP Production
Glycolysis' Role
Glycolysis provides the second anaerobic pathway for ATP production, primarily utilizing stored glucose.
Page 7: Direct Glucose Glycolysis
Glycolysis Process:
Breakdown of glucose into pyruvate or lactate yielding ATP through two phases: energy investment and energy generation.
Under anaerobic conditions, lactate is produced with a net yield of 2 ATP; under aerobic conditions, yields 38 ATP in oxidative phosphorylation.
Page 8: Oxygen's Role
Oxygen in Metabolism:
Critical during oxidative processes, allowing for greater energy production from substrates.
Important in understanding how glycolysis operates under varying oxygen availability.
Page 9: Reactions Overview in Glycolysis
Glycolysis involves nine reactions converting glucose to pyruvate, with significant ATP generation during the energy generation phase.
Net ATP yield after the full cycle is established based on the initial conditions set by glucose or glycogen usage.
Page 10: Energy Investment Phase Details
Initial Steps:
Glucose enters the cytosol and is phosphorylated by hexokinase; this step costs 1 ATP, creating glucose-6-phosphate.
Further rearrangement requires an additional ATP, totaling a cost of 2 ATP for the investment phase.
Page 11: Investment Phase Summary
Tallying ATP Costs:
Investment phase utilizes 2 ATP to maintain glucose in the cell, representing the 'priming' phase of glycolysis to add phosphates.
Page 12: Reaction Steps in Investment Phase
Key Reactions
Hexokinase Reaction: ATP costs 1 to phosphorylate glucose.
PFK Action: Costs another ATP to convert fructose-6-phosphate to fructose-1,6-bisphosphate.
Subsequent Reactions: Lead to the formation of glyceraldehyde-3-phosphate.
Page 13: Cleavage of Glucose
Splitting Glucose:
The 6-carbon glucose is cleaved into two 3-carbon molecules of glyceraldehyde-3-phosphate (G3P).
Page 14: Energy Tally at Investment Phase
Investment Phase Summary:
The cost of 2 ATP is recorded; during the energy generation phase, ATP produced is tracked and compared to total expenditure.
Page 15: Energy Generation Overview
Key Outputs:
For every G3P processed, 2 ATP are produced leading to a total of 4 ATP generated during this phase, after accounting for prior costs of ATP in investment phase.
Page 16: Total ATP Yield
Final Count:
Total ATP from glycolysis is calculated by deducting the investment (2 ATP) from total generated (4 ATP). Final tally yields a net gain of 2 ATP for anaerobic glycolysis.
Page 17: Summary of Glycolysis
Glucose enters the cell and is phosphorylated by hexokinase, costing 1 ATP.
The PFK step costs an additional ATP.
Total net gain is calculated: 4 ATP produced in energy generation, leading to a net of 2 ATP remaining.
Pyruvate can transform into lactate under anaerobic conditions.
Page 18: Energy Sources for Muscle
Sources:
Immediate Energy: Phosphocreatine
Non-Oxidative: Anaerobic Glycolysis
Oxidative: Aerobic Glycolysis
Distinguishing ATP yields based on availability of oxygen for glycolytic pathways included.
Page 19: Understanding Glycogen
Glycogen Facts:
Composed of long-branched glucose molecules, glycogen serves as a major carbohydrate storage form found in liver and muscle tissues.
Initially utilized during glycolysis, followed by blood glucose utilization when glycogen depletes.
Page 20: Role of NADH and FADH
Respiratory Partners:
NAD+ and FAD are critical for shuttling hydrogen ions during aerobic ATP production; conversion to NADH and FADH occurs through oxidation-reduction reactions.
Page 21: Lactate Formation Process
Conversion Process:
NADH generated in glycolysis must return to NAD+ for continued glycolytic function, typically through the conversion of pyruvate into lactate.
More details will follow in the discussions concerning aerobic and exercise metabolism.
Page 22: Oxidative Phosphorylation Overview
Oxidative Phase Mechanism:
Occurs in the mitochondria, consisting of three stages:
Generation of acetyl-CoA
Krebs Cycle
Electron Transport Chain