Energy, Enzymes, and Metabolism

Learning Objectives

• Define energy and its two major types: potential and kinetic.

• Understand the First and Second Laws of Thermodynamics.

• Comprehend Gibbs free energy and the tendency of systems to move towards low Gibbs free energy states.

• Differentiate between exergonic and endergonic reactions; understand their relation through energy coupling.

• Recognize activation energy as a barrier affecting the rate of chemical reactions.

• Define enzymes and describe their role in catalyzing chemical reactions.

• Identify factors affecting enzymatic activity, including environmental changes and phosphorylation.

• Distinguish between cofactors and coenzymes in enzymatic processes.

• Define metabolism and metabolic pathways, exploring the two types: anabolic and catabolic.

Types of Energy

• Energy: Capacity to do work or supply heat (making changes)

• Potential Energy:

  • Stored energy based on position or chemical bonds.

• Kinetic Energy:

  • Energy associated with movement (e.g., heat, motion).

Forms of Energy

• Heat

• Chemical

  • Thermal energy is a type of kinetic energy associated with the random movement of atoms or molecules

  • Potential energy available for release in a chemical reaction, most important type of energy for living organisms to power the work of the cell (ATP)

• Electric

• Light

• Radiation

• Sound

Thermodynamics- Study of energy transformation

First Law of Thermodynamics

• Energy cannot be created or destroyed, only transformed.

Second Law of Thermodynamics

• Energy transformations increase disorder and/or release heat. [electric to light/heat]

• Energy transformations are inefficient

Gibbs Free Energy (G)

• Defines the total potential energy available in a system to do work.

• Systems tend to move towards lower free energy states for stability:
  \Delta G = G{\text{end}} - G{\text{start}} $

• High G (more free energy)→Low G (less free energy)

Chemical Reactions

Exergonic Reactions (IN)

• Release energy, spontaneous reactions

• Products have less energy than reactants

• Breaks down things

• Products have lower potential energy:

  • Negative \Delta G indicates energy release.

Endergonic Reactions (OUT)

• Absorb energy, non-spontaneous reactions

• Building new things (like new bonds)

• Products have more energy than reactions

• Products possess higher potential energy:

  • Positive \Delta G$$ indicates energy absorption.

Energy Coupling

• The process where energy released from exergonic reactions powers endergonic reactions, frequently involving ATP.

Activation Energy (EA)

• Minimum energy required for reactants to convert into products.

• Enzymes facilitate reactions by stabilizing the transition state and lowering the activation energy barrier:

  • Activation energy lowers in the presence of enzymes.

• This is a barrier/obstacle for chemical reaction “slows down chemistry”

• APPLIES to ALL chemical reactions (exergonic or endergonic)

Enzymes - biological catalysts that speed up chemical reactions

Characteristics

• Biological catalysts that speed up reactions.

• Most enzymes are proteins, some can be RNA molecules (e.g., ribozymes).

• Enzymes lower the activation energy

Mechanism of Action

1. Substrate Binding: Enzymes are specific for their substrate based on a have (active site)

2. Induced Fit: Active site adjusts shape to better fit substrate, forming transition state.

3. Catalysis: Enzyme converts substrate to product, releasing it from active site.

Factors Affecting Enzyme Activity

• Environmental Factors:

  • Optimal pH, temperature, and salinity conditions for maximum activity.

• Phosphorylation:

  • Addition or removal of phosphate groups can activate or deactivate enzymes.

• Cofactors and Coenzymes:

  • Non-protein helpers aiding enzyme function (e.g., metal ions as cofactors, vitamins as coenzymes).

Metabolism

Definition

• Metabolism: All chemical reactions occurring in an organism.

• Metabolic Pathways: Series of reactions converting starting molecules to products.

Types of Pathways

• Anabolic Pathways: Consume energy to build large molecules from smaller ones.

• Catabolic Pathways: Release energy through the breakdown of large molecules into smaller ones.