Chapter: Metabolism

Introduction to Metabolism

Metabolism refers to the totality of an organism's chemical reactions, which are essential for maintaining life. These reactions are organized into metabolic pathways, each catalyzed by specific enzymes.

• Metabolism: The sum of all chemical reactions in a cell or organism.

• Metabolic Pathway: A series of chemical reactions that either build complex molecules (anabolic) or break down complex molecules (catabolic).

• Each step in a pathway is catalyzed by a specific enzyme.

• Metabolism manages the material and energy resources of the cell.

Types of Metabolic Pathways

• Catabolic Pathways: Release energy by breaking down complex molecules into simpler ones.

  • Example: Cellular respiration breaks down glucose to release energy.

• Anabolic Pathways: Consume energy to build complex molecules from simpler ones.

  • Example: Synthesis of amino acids or proteins.

Energy in Biological Systems

Energy is the capacity to cause change. In biological systems, energy is required for various cellular processes.

• Kinetic Energy: Energy related to motion.

• Thermal Energy: Kinetic energy associated with the random movement of atoms or molecules.

• Potential Energy: Energy related to location or structure.

• Chemical Energy: Potential energy available for release in a chemical reaction.

Thermodynamics in Biology

First Law of Thermodynamics

The first law states that energy can be transferred and transformed, but it cannot be created or destroyed. This is also known as the principle of conservation of energy.

Second Law of Thermodynamics

The second law states that every energy transfer or transformation increases the entropy of the universe.

• Entropy: A measure of molecular disorder or randomness.

• Spontaneous processes increase entropy and can proceed without requiring an input of energy.

• Non-spontaneous processes decrease entropy and require energy input.

Spontaneous and Non-Spontaneous Processes

• Spontaneous Process: Occurs without energy input; increases entropy.

• Non-Spontaneous Process: Requires energy input; decreases entropy.

Free Energy and Work

Free energy is the portion of a system's energy that can perform work when temperature and pressure are uniform throughout the system.

• Change in free energy is calculated using the formula: where is the change in free energy, is the change in enthalpy (total energy), is temperature in Kelvin, and is the change in entropy.

• Negative indicates a spontaneous process.

• Positive indicates a non-spontaneous process.

Equilibrium and Free Energy

• For a reaction to have a negative , the system must lose free energy during the change from initial to final state.

• Lower free energy means the system is more stable.

• Free energy increases when a reaction is pushed away from equilibrium.

• Systems never spontaneously move away from equilibrium.

• At equilibrium, a system cannot spontaneously change or do work.

Exergonic and Endergonic Reactions

• Exergonic Reaction: Releases free energy; is negative; occurs spontaneously.

• Endergonic Reaction: Absorbs free energy; is positive; non-spontaneous.

Summary Table: Types of Metabolic Pathways

Summary Table: Types of Reactions

Additional info:

• Enzymes play a critical role in lowering activation energy and speeding up metabolic reactions.

• Cells use energy coupling, often via ATP, to drive endergonic reactions.