4.1 (3)

Learning Objectives

• Understand the concept of bioenergetics and energy flow through living systems.

• Explain metabolic pathways and their significance in cellular processes.

• State the first and second laws of thermodynamics.

• Differentiate between kinetic and potential energy.

• Describe endergonic and exergonic reactions.

• Discuss the functioning of enzymes as molecular catalysts.

Bioenergetics and Metabolism

• Bioenergetics: Refers to energy flow through living systems, particularly in cells.

• Metabolism: Encompasses all chemical reactions in cells, including energy-consuming and energy-generating processes.

  • Metabolic pathways involve stepwise reactions using and producing energy.

  • Cells must continuously obtain energy to sustain metabolic activities.

Metabolic Pathways

• Example of Sugar Metabolism: Central to energy production in living organisms.

• Photosynthesis: Plants convert carbon dioxide (CO2) into sugars using sunlight, producing oxygen as a by-product:

  • Reaction: 6CO2 + 6H2O → C6H12O6 + 6O2

• Anabolic Pathways: Synthesize larger molecules (requires energy).

• Catabolic Pathways: Break down larger molecules into smaller ones (releases energy).

• Important to maintain energy balance in cells.

Thermodynamics in Biological Systems

• Energy Definition: The capacity to do work or effect change; exists in various forms (electrical, light, heat).

• Open Systems: Biological organisms are open systems, exchanging energy with the environment.

First Law of Thermodynamics

• Energy is conserved; it cannot be created or destroyed, only transformed.

• Example: Plants convert sunlight to chemical energy.

Second Law of Thermodynamics

• Energy transfers are never 100% efficient, leading to some energy being lost as heat.

• Increased entropy (disorder) occurs when energy is lost.

Types of Energy

• Kinetic Energy: Energy in motion (e.g., moving objects, molecules).

• Potential Energy: Stored energy based on position (e.g., high-lifted wrecking ball, chemical bond energy).

• Chemical Energy: Energy stored within molecular bonds, released during metabolism.

Free and Activation Energy

• Free Energy (∆G): Energy available for work after losses; negative ∆G indicates spontaneous (exergonic) reactions, while positive ∆G indicates non-spontaneous (endergonic) reactions.

• Activation Energy: Minimum energy needed for a reaction to proceed; exergonic reactions still require some energy input to initiate.

Enzymes as Catalysts

• Catalysts: Substances that speed up chemical reactions (enzymes are primarily proteins).

• Enzymes lower activation energy, facilitating reactions without altering reaction outcomes.

  • Bind to substrates, forming an enzyme-substrate complex, promoting reaction.

• Active Site: Specific site on an enzyme where substrates bind and reactions occur.

Enzyme Functionality

• Enzymes are influenced by temperature, pH, and concentration; extreme conditions can lead to denaturation.

• Induced Fit Model: Describes a dynamic interaction between the enzyme and substrate, adjusting to enhance binding and catalysis.

Regulation of Enzyme Activity

• Enzyme activity can be modulated based on cellular conditions, including:

  • Competitive Inhibition: Inhibitor competes with substrate for active site.

  • Noncompetitive Inhibition: Inhibitor binds to a different site, altering enzyme function.

  • Allosteric Regulation: Binding at allosteric sites affects enzyme activity—can be both inhibitors and activators.

Feedback Inhibition in Metabolic Pathways

• Cells utilize products of metabolic reactions to regulate enzymes, slowing or accelerating production as needed.

• Example: ATP regulates the breakdown of sugar; high ATP levels inhibit while ADP levels promote ATP production.

• Important regulatory mechanism in maintaining cellular energy balance.