lecture recording on 10 March 2025 at 12.58.42 PM

Introduction to Metabolism

• Metabolism encompasses all chemical reactions occurring within living organisms.

• The focus is on cellular respiration and photosynthesis along with fermentation.

• Understanding these reactions requires a return to basic science principles involving chemistry and physics.

Energy in Metabolic Reactions

• Living systems require a constant input of energy to maintain homeostasis, as energy is lost to surroundings.

• Energy Definition: The capacity to perform work and cause change.

• Types of energy:

  • Kinetic Energy: Measurable change in energy due to movement (e.g., waterfall).

  • Potential Energy: Stored energy that can be converted to kinetic energy; cannot be directly measured but inferred from kinetic energy transformations.

Energy Transformations

• Energy transformations occur as kinetic energy is turned to potential energy and vice versa.

• Example with biking: Climbing a hill (potential) transforms to rapid descent (kinetic) as gravity pulls down.

• System vs. Surroundings:

  • System: the matter under study.

  • Surroundings: everything around the system that can exchange energy with it.

Laws of Thermodynamics

• First Law: Energy cannot be created or destroyed, only transformed. The total energy in a closed system remains constant.

  • Energy is simply transferred; for example, eating food transforms potential energy into kinetic energy for movement.

• Second Law: Energy transformations are not 100% efficient; some energy disperses as heat (entropy).

  • Entropy increases as energy spreads out, leading to randomness and disorder in the system.

Measuring Energy in Chemical Reactions

• Exergonic Reactions: Release energy; typically have a negative Gibbs free energy change.

• Endergonic Reactions: Require energy input to proceed; typically have a positive Gibbs free energy change.

• Activation Energy: Initial energy required to begin a reaction; necessary for both exergonic and endergonic processes.

Metabolic Pathways

• Metabolism is divided into two categories:

  • Anabolic Pathways: Use energy to build larger molecules (e.g., synthesis of proteins).

  • Catabolic Pathways: Break down larger molecules, releasing energy (e.g., cellular respiration).

• Energy Coupling: Using energy from exergonic reactions to fuel endergonic reactions, ensuring efficiency and continued function of cells.

ATP (Adenosine Triphosphate) Cycle

• ATP functions as an energy currency in cells, capturing and donating energy as needed.

• Phosphorylation: The process of adding a phosphate group to an molecule, requiring energy, and is typically performed using ATP.

• ATP is regenerated from ADP and inorganic phosphate using energy from cellular processes.

Cellular Respiration

• Cellular respiration is a series of metabolic reactions used to convert biochemical energy from nutrients into ATP.

  • Occurs in several stages: Glycolysis, Krebs Cycle, and Electron Transport Chain.

• Each step of cellular respiration releases energy in a controlled manner (compared to combustion in gasoline engines).

Photosynthesis

• Photosynthesis is the process by which plants and certain organisms convert light energy into chemical energy (glucose).

• Involves light absorption, water splitting (releasing oxygen), and fixation of carbon dioxide into carbohydrates.

• It is important for sustaining energy flow in ecosystems.

Implications of Thermodynamics in Biology

• Living organisms must navigate thermodynamic laws to efficiently convert energy and maintain metabolic function.

• Catabolic and anabolic reactions are tightly regulated and coupled to meet the energy demands of the cell.