Energy and Enzymes

Role of Energy in Living Organisms

Energy is essential for all living organisms, enabling them to perform cellular processes, grow, reproduce, and maintain homeostasis. Organisms must continually input energy to offset energy loss and sustain life.

• Energy Input vs. Energy Loss: Living things require energy input to exceed energy loss for survival.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe.

• Metabolic Pathways: Sequential series of chemical reactions in cells, organized as catabolic (breaking down molecules, releasing energy) or anabolic (building molecules, requiring energy).

• Potential Energy: Stored energy due to position or structure.

• Chemical Energy: Energy stored in chemical bonds.

Free Energy and Spontaneity of Reactions

The change in free energy (ΔG) determines whether a reaction occurs spontaneously. Spontaneous reactions release energy, while non-spontaneous reactions require energy input.

• Free Energy (ΔG): The portion of a system's energy available to do work.

• Equation for ΔG:

• Positive ΔG: Non-spontaneous, endergonic reactions (require energy).

• Negative ΔG: Spontaneous, exergonic reactions (release energy).

• Chemical Equilibrium: State where forward and reverse reactions occur at equal rates.

• Exergonic Reaction: Releases energy; ΔG is negative.

• Endergonic Reaction: Requires energy input; ΔG is positive.

• ΔG for Photosynthesis: Positive (endergonic).

• ΔG for Respiration: Negative (exergonic).

ATP and Cellular Work

ATP (adenosine triphosphate) is the primary energy carrier in cells. It powers cellular work by coupling exergonic and endergonic reactions.

• Structure of ATP: Consists of adenine, ribose, and three phosphate groups.

• ATP → ADP: Hydrolysis releases energy; conversion requires energy.

• Energy Coupling: Using energy released from exergonic reactions to drive endergonic reactions.

• Phosphorylation: Transfer of a phosphate group to another molecule, making it more reactive.

• Regeneration of ATP: ATP is regenerated from ADP and inorganic phosphate using energy from catabolic reactions.

Enzymes and Metabolic Reactions

Enzymes are biological catalysts that speed up metabolic reactions by lowering activation energy barriers. They are essential for life, enabling reactions to occur rapidly and efficiently under cellular conditions.

• Enzyme: Protein that catalyzes chemical reactions.

• Catalyst: Substance that speeds up a reaction without being consumed.

• Activation Energy (EA): Energy required to initiate a reaction.

• Transition State: High-energy, unstable state during a reaction.

• Enzyme's Effect: Lowers EA, does not change ΔG.

• Substrate: Reactant molecule acted upon by an enzyme.

• Active Site: Region of enzyme where substrate binds.

• Induced Fit: Enzyme changes shape to fit substrate more closely.

• Enzyme-Substrate Complex: Temporary association between enzyme and substrate.

• Substrate Specificity: Enzymes are highly specific for their substrates.

• Catalytic Cycle: Sequence of events in enzyme action (binding, catalysis, release).

• Four Mechanisms to Lower EA: Orienting substrates, straining bonds, providing favorable microenvironment, covalently bonding to substrate.

Factors Affecting Enzyme Activity

Enzyme activity is influenced by environmental conditions and concentrations of substrates, enzymes, and inhibitors.

• Temperature: Optimal range increases activity; extreme temperatures cause denaturation.

• pH: Each enzyme has an optimal pH; deviations can denature the enzyme.

• Substrate Concentration: Higher concentration increases rate until enzyme is saturated.

• Enzyme Concentration: More enzyme increases reaction rate.

• Competitive Inhibitor: Binds to active site, blocking substrate.

• Noncompetitive Inhibitor: Binds elsewhere, changing enzyme shape.

• Cofactor/Coenzyme: Non-protein helpers required for enzyme activity.

• Denaturation: Loss of enzyme structure and function due to environmental changes.

• Permanent/Reversible Inhibition: Inhibitors may bind permanently or reversibly.

Conservation of Metabolic Pathways

Core metabolic pathways, such as glycolysis and the citric acid cycle, are conserved across all domains of life. This conservation supports the concept of common ancestry for all organisms.

• Evidence for Common Ancestry: Shared, fundamental processes and features among diverse organisms.

Summary Table: Types of Enzyme Inhibition

Example: Cyanide acts as an irreversible inhibitor of cytochrome c oxidase, halting cellular respiration.

Additional info: The provided image (image_1) is a blank graph and does not directly illustrate any of the above concepts, so it is not included.