05_Glycolysis_Krebs Cycle
Glycolysis and the Krebs Cycle
Page 1: Overview
Introduction to Glycolysis and the Krebs Cycle
Page 2: Key Concepts in Thermodynamics
Energy Flow
Energy flows from one place to another.
Energy flows downhill, indicating a natural tendency towards lower energy states.
Spontaneous Events
Events must be spontaneous, occurring with the release of free energy.
Spontaneous does not imply speed; it simply means that reactions can occur without external work.
Equilibrium in Enzyme-Catalyzed Reactions
Closed systems still reach equilibrium despite catalyst presence.
Page 3: Topics Covered
Nutrient Energy Capture
Focus on how cells capture free energy from nutrients.
Glycolysis
Anaerobic pathway for energy generation from glucose.
Krebs Cycle
The initial aerobic pathway of respiration.
Energy Capture Mechanisms
Gluconeogenesis
Reversal of glycolysis; importance for cellular function.
Page 4: Respiration Summary Equation
General Equation:
C6H12O6 + 6O2 → 6CO2 + 6H2O
Free Energy Change:
ΔG0 = -687 kcal/mol
ATP Production Potential
Theoretical ATP generation from glucose combustion requires understanding ATP hydrolysis energetics.
Page 5: Energy Flow in Living Things
Energy Sources:
Visible Light (Photo-autotrophs)
Energy captured via photosynthesis; results in chemical energy (glucose).
Nutrient Energy (Oxidative Reactions)
Source of energy through chemical fermentation and respiration, generating ATP.
High Energy Intermediates
ATP produced coupled with cellular work (e.g., metabolism, growth).
Page 6: ATP Hydrolysis and Cellular Work
Hydrolysis vs. Condensation Reaction
Hydrolysis releases free energy for cellular work (e.g., movement, synthesis).
Nutrient Sources
Animal cells derive energy to synthesize ATP solely from nutrients.
Photosynthetic organisms utilize sunlight to synthesize nutrients.
Page 7: ATP Generation from Nutrients
Glucose Oxidation Reaction:
C6H12O6 + 6O2 → 6CO2 + 6H2O
Energy Calculations:
Encompasses glycolysis, TCA cycle, and electron transport.
Approx. 36 ATP + 36 H₂O produced.
Total Energy from Glucose: 263 Kcal/mole oxidized.
Page 8: Glycolysis Overview
Universal Pathway
Present in all organisms; indicates evolutionary significance.
Location: Cytosol
Breakdown Process
Each glucose splits into two pyruvic acid molecules, yielding 2 ATP in the process.
Pathway Stages
Glycolysis occurs in two stages: energy investment and energy payoff.
Page 9: Glycolysis Process
Stage 1: Splitting of Glucose
Involves ATP consumption to form intermediates (e.g. fructose-1,6-diphosphate).
Stage 2: Production of Pyruvate
Involves generation of ATP through substrate-level phosphorylation.
Key enzyme: phosphoenolpyruvate to pyruvate, yielding ATP.
Page 10: Pyruvate Fates
Anaerobic Metabolism:
Produces lactate, alcohol, or dibasic acids via fermentation.
Aerobic Metabolism:
Further oxidation to CO₂ and H₂0 within mitochondria.
Page 11: Glycolysis Mechanism
Reaction 1:
Coupled phosphorylation of glucose with ATP hydrolysis; exergonic and irreversible in cells.
Page 12: Hexokinase Energetics
Standard Conditions:
Glucose phosphorylation as the sum of reactions.
Reaction energetics yield an exergonic action with the following values:
ATP + G → G-6-P; ΔG < 0 for irreversible phosphorylation.
Page 13: Regulatory Mechanisms
Biological Irreversibility:
Glucose cannot exit once phosphorylated (by hexokinase).
Allosteric Regulation:
Glucose-6-Phosphate inhibits hexokinase, conserving cellular resources.
Page 14: Enzymatic Reactions
G-6-P Isomerase
Mildly endergonic; reversible transformation of glucose-6-phosphate to fructose-6-phosphate.
Page 15: Enzyme Regulation Overview
Factors Affecting Enzyme Activity:
ATP (inhibitory), ADP (activating), AMP (activating), fatty acids (variable impact).
Page 16: Reactions in Glycolysis
F-1,6-DiP Aldolase:
Formation of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate; energetically uphill but reversible.
Page 17: Enzyme Regulation and Reaction Dynamics
Enzyme, triose-P-isomerase exhibits negative cooperativity regulated by NAD+ concentration for efficient reaction acceleration.
Page 18: Energy Transfer in Glycolysis
Exergonic Reaction:
Phosphate transfer yielding spontaneous reactions;
Page 19: Mutase Functionality
P-glyceromutase:
Phosphate group transferring mutases that operate freely and reversibly.
Page 20: End of Glycolysis Reactions
Enolase activity with phosphate involves reversible actions; mildly endergonic.
Page 21: Reaction Irreversibility in Glycolysis
Highly exergonic, regulated by various metabolites and feedback mechanisms; predict impacts of ATP and intermediates.
Page 22: Efficiency of Pathways
Comparison between fermentation and aerobic respiration, highlighting efficiency differences based on NADH and ATP contributions.
Page 23: Introduction to Gluconeogenesis
Stored glucose converted to glycogen in well-fed states; controlled by glucagon and insulin.
Gluconeogenesis using pyruvate, lactate, glycerol, and amino acids for glucose production.
Page 24: Glycolysis vs. Gluconeogenesis
Shared intermediates with distinct pathways; inverse reactions controlled via bypass enzymes to regulate cellular carbohydrate levels.
Page 25: The Cori Cycle
Connection between glycolysis and gluconeogenesis.
Muscle cells convert glucose to lactate; the liver rejuvenates glucose from lactate through gluconeogenesis.
Page 26: Hormonal Impact on Gluconeogenesis
Hormonal regulation from the hypothalamus to control gluconeogenesis through metabolic pathways.
Page 27: Dietary Implications
Ultra-low carb diets effect on weight loss and blood sugar control in individuals with type 2 diabetes.
Insights into metformin's role in blood sugar regulation.
Page 28: Introduction to Krebs Cycle
Significance of oxygen presence for efficient respiration and ATP production; all aerobic organisms including plants utilize the Krebs Cycle.
Page 29: Pyruvate Oxidation
Catalyzed by pyruvate dehydrogenase, producing acetyl-S-CoA for the Krebs Cycle; complete oxidation and energy capture mechanisms in the mitochondria.
Page 30: Energy Release from Pyruvate
Pyruvate enters mitochondria, initiates the Krebs Cycle; carbon dioxide produced, with energy captured in reduced e- carriers.
Page 31: Free Energy Storage in Respiration
Total free energy stored per NADH and FADH2 produced; efficiency of ATP synthesis per glucose oxidized.