Making Life Possible II - Energy Generation and Metabolism Flashcards
Energy and Entropy
Entropy means disorder, randomness, uncertainty
First law: ‘Energy can neither be created nor be destroyed, it can only be transferred from one form to another’
Second law: ‘The entropy of any isolated system always increases’.
How do living systems maintain low entropy?
Entropy tends to increase with time. A living system maintains low entropy by being open to flows of energy and mass.
Gibbs Free Energy (Delta G)
Delta G (units kJ/mol) is a thermodynamic potential reflecting the maximum amount of work performable (available energy) by a thermodynamically closed system at a constant temperature and pressure.
Actual delta G is a function of standard delta G^0 and the actual concentrations of reactants.
Three cases:
Equilibrium reaction delta G = 0
Exergonic reaction delta G is negative, products have less free energy than reactants, free energy released. Reaction can proceed forward.
Endergonic reaction delta G is positive, products have more free energy than reactants, free energy is required for reaction to proceed forward.
Delta G^0 equation
Delta G^0 = -RT ln Keq (equilibrium constant)
Equilibrium constant (Keq)
[Product]/[Substrate] ignoring stoichiometry
Le Chatelier’s principle
Le Chatelier’s principle - a system responds to perturbation by acting to alleviate it.
Metabolic energy (delta G) uses
- Ion transport, creating transmembrane potential gradients, allowing impulse propagation
- Mechanical force: actomyosin (muscle), kinesin & dyneins (microtubules: organelles, flagella)
- Chemical synthesis (anabolism)
Others e.g. bioluminescence
How is Energy supplied?
At the point of use, energy is almost invariably supplied by ATP hydrolysis
ATP is made by processes of catabolism.
ATP/ADP system is thereby an intermediary, an ‘energy currency’.
Gibbs Free Energy (Delta G)
Delta G (units kJ/mol) is a thermodynamic potential reflecting the maximum amount of work performable (available energy) by a thermodynamically closed system at a constant temperature and pressure.
Actual delta G is a function of standard delta G^0 and the actual concentrations of reactants.
Three cases:
Equilibrium reaction delta G = 0
Exergonic reaction delta G is negative, products have less free energy than reactants, free energy released. Reaction can proceed forward.
Endergonic reaction delta G is positive, products have more free energy than reactants, free energy is required for reaction to proceed forward.
ATP supply and use
Gibbs free energy of ATP hydrolysis (delta G) determines energy available per ATP, and is an important regulatory signal.
Variations in delta G (ATP) can be an important metabolic signal, it cannot be allowed to vary too much.
Creatine Kinase
Note: Creatine kinase, in e.g. muscle and brain, ‘buffers’ temporary mismatch of ATP supply and demand.
Ways of producing glucose
Substrate Level Phosphorylation
Oxidative Phosphorylation
Substrate Level Phosphorylation
Substrate level phosphorylation - uses ADP and a phosphate-containing substrate e.g. PEP or ADP.
PEP + ADP <-> Pyruvate + ATP (Pyruvate kinase)
2ADP <-> ATP + AMP (adenylate kinase)
Metabolism
Anabolism + Catabolism = Metabolism
Catabolism is the breaking down of molecules which provides energy.
Anabolism is the synthesis of molecules which uses energy.
Catabolism: Glucose
Glycolysis:
Redox stoichiometry - Generates 2 NADH, either reduce pyruvate to lactate, or oxidised in electron transport chain (ETC).
ATP Stoichiometry - uses 2 ATP, generates 2 x 2 ATP so net yield = 2 ATP (Extra p from 2 Pi)
Fates of Pyruvate
Anaerobic conditions: Lactate (human), ethanol (yeast)
Fed state: Cellular respiration, via Acetyl CoA, the TCA cycle and oxidative phosphorylation
Fasting state: Gluconeogenesis via oxaloacetate
Also transamination, to amino acids.
Tricarboxylic Acid Cycle
= Krebs cycle = Citric acid cycle
Cycle of chemical reaction that oxidises acetyl CoA derived from carbohydrates, fats or proteins.
Produces 1 GTP directly, but most ‘oxidative’ ATP comes from oxidation of 3 NADH and 1 FADH2 via oxidative phosphorylation.
Oxidative Phosphorylation
Electron transport chain (ETC) = Respiratory Transport Chain
Located in the inner mitochondrial membrane
A series of components that oxidise reducing equivalents and use the energy to make ATP.
Electron Transport Chain
In the mitochondrion, a series of linked reactions couple the oxidation of NADH and FADH2 with the transfer of electrons and pumping of H+ ions into the intermembrane space, the resulting gradient drives ATP synthesis.
Here the coupling between exergonic substrate oxidation and endergonic ATP synthesis is a transmembrane H+ gradient.
ATP synthesis is driven by the chemiosmotic movement of H+ down this gradient.
Stoichiometry
Stoichiometry = ratios between quantities of reactants and products
