Energy

Energy Usage in Systems
- Free energy in a system can be used until depleted.
- Open systems can continuously import energy, thus maintaining functionality.
- Closed systems eventually reach metabolic equilibrium, which is detrimental for life.
Metabolic Pathways
- Enzymes catalyze reactions in metabolic pathways.
- Pathways consist of initial reactants, intermediates, and end products.
- Continuous supply of reactants is necessary to sustain reactions (prevent equilibrium).
- Equilibrium leads to a stable, unchanging mixture of reactants and products, which is lethal for living cells.
Work Done by Cells
- Cells perform various types of work:
- Physical movement: e.g., vesicle transport, active transport, flagella movement.
- Energy is derived from exergonic (catabolic) reactions to power endergonic (anabolic) reactions.
- Full energy recovery from exergonic reactions is not possible due to heat loss.

Structure of ATP
- Composed of adenosine and three phosphate groups.
- Hydrolysis of the terminal phosphate releases approximately 7.3 kilocalories per mole, providing usable energy.
- ATP acts as the primary energy currency in cells.
Reaction Mechanisms
- Exergonic reactions release energy; endergonic reactions require energy.
- ATP hydrolysis provides energy for cellular processes.
- Phosphorylation: Transfer of a phosphate group from ATP to another molecule, activating it for further reactions.
Chemical Equilibrium and Energy
- Chemical reactions tend toward equilibrium but living cells maintain non-equilibrium states through constant input of energy.
- Examples include phosphorylation that activates substrates to participate in reactions, pushing them toward product formation.

Energy Laws
- Energy is conserved; it can neither be created nor destroyed but transformed.
- Chemical reactions entail energy changes that depend on the type and direction of the reaction.
Enzyme Functionality
- Enzymes lower activation energy, increasing the rate of reactions without being consumed themselves.
- An enzyme-substrate complex undergoes a transition state to facilitate bond breaking and formation.
- Catalysis is specific, with each enzyme designed for specific substrates through a lock-and-key model.
- Induced fit model describes how enzymes slightly change shape when binding substrates, enhancing the interaction.

Metabolic Efficiency
- Enzymes enhance metabolic efficiency by significantly reducing activation energies, allowing more reactions to occur in less time.
- Each enzyme remains unchanged after a reaction and can be reused multiple times.
Specificity
- Enzymes are selective for specific substrates based on the active site's shape, which matches specific chemical properties.
- The enzyme's active site undergoes conformational changes to stabilize transition states during reactions.
Environmental Conditions
- Optimal pH and temperature conditions are essential for enzyme functionality.
- Different enzymes and metabolic processes function under distinct environmental conditions that affect enzyme activity (e.g., stomach vs. pancreatic enzymes).
Internal Regulation
- The body maintains homeostasis by regulating enzyme activity and conditions in various internal compartments, ensuring that biochemical reactions occur efficiently and appropriately.

Metabolic Pathways and Energy Use
- Life operates through a series of complex reactions mediated by enzymes, wherein energy flow is crucial.
- Understanding these principles is essential in biology, providing insights into cellular processes and the maintenance of life in organisms.
Future Studies
- Explore advanced topics like signal transduction pathways involving enzymes, energy metabolism in different organisms, and the impact of enzyme inhibitors on biological processes.