An Introduction to Metabolism and Free Energy

Chapter 8: An Introduction to Metabolism and Free Energy

Metabolic Pathways

1. Metabolism is defined as the totality of an organism's chemical reactions.

2. Catabolic pathways are metabolic processes that release energy by breaking down complex molecules into simpler compounds.

   • Example: Cellular respiration, which breaks down glucose.

3. Anabolic pathways are metabolic processes that consume energy to build complicated molecules from simpler compounds.

   • Example: The creation of proteins by combining amino acids.

4. Crucially, the energy released by catabolic pathways is used to drive anabolic pathways, creating a continuous cycle of energy transformation and utilization within an organism.

Energy

1. Energy is the capacity to cause change, and specific forms of energy can be harness to perform work.

   • Work involves moving matter against opposing forces, such as gravity or friction.

   • Energy is fundamentally the ability to rearrange a collection of matter.

2. Kinetic energy is the energy associated with moving matter. Moving objects can perform work by imparting motion to other matter.

   • Examples: Moving electrons (electricity), light, heat, and muscles contracting to push bike pedals.

3. Potential energy is the energy that matter possesses due to its location or structure.

   • Example: The arrangement of electrons in the bonds between atoms.

   • Chemical energy is a specific type of potential energy available for release in a chemical reaction. For instance, the bonds within food molecules possess high potential energy or chemical energy.

4. Cellular respiration and other catabolic pathways liberate energy stored in organic molecules. This released energy becomes available for cellular work. The chemical energy initially stored in these organic molecules was primarily derived from light energy by plants during photosynthesis.

5. A central, defining property of living organisms is their ability to transform energy from one form to another.

   • Water Wheel Diagram Concept: The diagram illustrating energy typically shows water at a high elevation (A: High potential energy) falling, generating motion (C: Kinetic energy), and eventually reaching a lower elevation (B: Low potential energy).

Thermodynamics

1. Thermodynamics is the scientific study of energy transformations.

   • The system indicates the specific matter under study, and the surroundings encompass everything outside that system.

   • A closed system, exemplified by liquid in a thermos, is isolated from its surroundings, meaning no exchange of materials or energy occurs between the system and the surroundings.

   • Open systems exchange or transfer both materials and energy between the system and the surroundings.

     • Organisms are inherently open systems. They continually absorb energy (e.g., food, light), release heat, and excrete metabolic waste products.

2. The 1st Law of Thermodynamics (Law of Conservation of Energy) states that energy can be transferred and transformed, but it cannot be created or destroyed.

   • Example: Plants transform light energy into chemical energy during photosynthesis.

3. The 2nd Law of Thermodynamics states that every energy transformation must make the universe more disordered.

   • Entropy is a quantity used as a measure of disorder or randomness.

   • This disorder often manifests in the form of heat, which is energy in its most random and