Introduction to Metabolism

Overview of Metabolism

Metabolism refers to the totality of an organism’s chemical reactions, which are organized into metabolic pathways. These pathways manage the material and energy resources of the cell, allowing it to grow, reproduce, and respond to environmental changes.

• Metabolism: The sum of all chemical reactions occurring in a living organism.

• Metabolic Pathways: Series of chemical reactions that either build complex molecules (anabolic) or break them down (catabolic).

• Example: Cellular respiration is a catabolic pathway that breaks down glucose to release energy.

Types of Metabolic Pathways

Catabolic and Anabolic Pathways

Metabolic pathways are classified based on whether they release or consume energy.

• Catabolic Pathways: Break down complex molecules into simpler ones, releasing energy.

• Anabolic Pathways: Build complex molecules from simpler ones, consuming energy.

• Example: Synthesis of proteins from amino acids is an anabolic pathway.

Thermodynamics and Cells

Basic Principles of Thermodynamics

Thermodynamics is the study of energy transformations. The laws of thermodynamics apply to all energy exchanges, including those in biological systems.

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

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

• Entropy: A measure of molecular disorder or randomness.

• Example: During cellular respiration, some energy is lost as heat, increasing entropy.

Spontaneity of Chemical Reactions

Spontaneous vs. Nonspontaneous Processes

Spontaneous processes occur without an input of energy and increase the entropy of the universe. Nonspontaneous processes require energy input.

• Spontaneous Process: Occurs naturally, energetically favorable, increases entropy.

• Nonspontaneous Process: Requires energy input, does not increase entropy on its own.

• Note: Spontaneous does not mean fast; some spontaneous reactions can be slow.

Free Energy and Chemical Reactions

Gibbs Free Energy ()

Gibbs free energy is the portion of a system’s energy that can perform work at constant temperature and pressure. The change in free energy () determines whether a reaction is spontaneous.

• Equation:

• : Change in free energy

• : Change in enthalpy (total energy)

• : Temperature in Kelvin

• : Change in entropy

• Spontaneous reactions have (negative free energy change).

• Nonspontaneous reactions have (positive free energy change).

Exergonic and Endergonic Reactions

Classification of Reactions by Free Energy Change

Chemical reactions are classified based on the direction of free energy change.

• Exergonic Reaction: Releases free energy, , spontaneous.

• Endergonic Reaction: Absorbs free energy, , nonspontaneous.

• Example: ATP hydrolysis is exergonic; synthesis of glucose from CO2 and H2O is endergonic.

Cells and Energy Equilibrium

Open vs. Closed Systems

Cells are open systems, constantly exchanging energy and matter with their surroundings. This prevents them from reaching equilibrium, allowing continuous work and life processes.

• Open System: Exchanges energy and matter with the environment (e.g., living cells).

• Closed System: No exchange of energy or matter with the environment.

• Example: Cells maintain a constant flow of materials and energy to sustain life.

Summary Table: Key Concepts in Metabolism and Thermodynamics