Energy in Biological Systems

Potential Energy and Chemical Potential Energy

Energy is fundamental to all biological processes. In living organisms, energy exists in various forms, including potential energy, which is stored based on the position or structure of objects or molecules.

• Potential Energy: The energy stored due to an object's position or arrangement. For example, a ball held at a height has gravitational potential energy.

• Chemical Potential Energy: The energy stored within the chemical bonds of molecules. This energy can be released during chemical reactions, such as the breakdown of glucose in cellular respiration.

• Example: The energy stored in the bonds of ATP (adenosine triphosphate) is a key source of chemical potential energy for cells.

Types of Energy Relevant to Biology

• Kinetic Energy: The energy of motion. For example, moving muscles or the flow of ions across membranes.

• Thermal Energy: The energy associated with the random movement of atoms and molecules; often released as heat.

• Application: Organisms convert chemical potential energy from food into kinetic and thermal energy to perform work and maintain homeostasis.

Thermodynamics in Biology

Open and Closed Systems

Biological systems interact with their environment, exchanging energy and matter.

• Open System: Exchanges both energy and matter with its surroundings. Living organisms are open systems.

• Closed System: Exchanges energy but not matter with its surroundings. A thermos bottle is an example, though not perfectly closed.

• Example: A platypus is an open system, taking in food, water, and oxygen, and releasing waste and heat.

The Laws of Thermodynamics

• First Law (Law of Conservation of Energy): Energy can be transferred and transformed, but it cannot be created or destroyed. In biological systems, energy is transformed from one form to another (e.g., chemical to kinetic), but the total amount remains constant.

• Second Law (Law of Entropy): Every energy transfer or transformation increases the entropy (disorder) of the universe. Some energy becomes unusable, often lost as heat.

• Example: When a bear eats a fish, not all the energy from the fish is converted into usable energy for the bear; some is lost as heat or waste.

Key Equations

• First Law: (Change in internal energy equals heat added plus work done on the system)

• Second Law: (The entropy of the universe always increases in a spontaneous process)

Energy Transformations and Entropy

Entropy in Biological Systems

Entropy is a measure of disorder or randomness. Biological processes tend to increase the entropy of the universe, even as organisms maintain internal order.

• Entropy (): A thermodynamic quantity representing the unavailability of a system's energy to do work.

• Application: When organisms use energy, some is always lost as heat, increasing the entropy of the surroundings.

• Example: The breakdown of glucose during cellular respiration releases energy and increases entropy.

Chemical Reactions and Free Energy

Spontaneous and Non-Spontaneous Reactions

Chemical reactions in cells can be classified based on whether they occur spontaneously (without input of energy) or require energy input.

• Spontaneous Reaction: Occurs without the need for additional energy; usually releases free energy and increases entropy.

• Non-Spontaneous Reaction: Requires an input of energy to proceed.

• Example: The hydrolysis of ATP is a spontaneous reaction that releases energy for cellular work.

Free Energy and the Gibbs Free Energy Equation

Free energy determines whether a reaction can occur spontaneously. The change in free energy () is a key concept in biochemistry.

• Gibbs Free Energy (): The energy in a system that can be used to do work at constant temperature and pressure.

• Equation:

• = change in free energy

• = change in enthalpy (total energy)

• = temperature in Kelvin

• = change in entropy

• Interpretation: If is negative, the reaction is spontaneous. If $\Delta G$ is positive, the reaction is non-spontaneous.

• Example Calculation: If the free energy of reactants is higher than that of products, is negative and the reaction will proceed spontaneously.

Endergonic and Exergonic Reactions

Biological reactions are often classified as exergonic (energy-releasing) or endergonic (energy-consuming).

Metabolic Pathways and Energy Coupling

Metabolic Pathways

Metabolic pathways are series of chemical reactions occurring within a cell. These pathways can be catabolic (breaking down molecules to release energy) or anabolic (building molecules, requiring energy input).

• Catabolic Pathways: Break down complex molecules into simpler ones, releasing energy (e.g., glycolysis, cellular respiration).

• Anabolic Pathways: Build complex molecules from simpler ones, consuming energy (e.g., protein synthesis, photosynthesis).

ATP and Energy Coupling

ATP (adenosine triphosphate) is the primary energy currency of the cell. It couples exergonic and endergonic reactions, allowing energy released from one reaction to drive another.

• ATP Hydrolysis: The breakdown of ATP into ADP and inorganic phosphate releases energy that can be used for cellular work.

• Energy Coupling: The process by which the energy released from exergonic reactions (like ATP hydrolysis) is used to power endergonic reactions.

• Example: Muscle contraction is powered by the hydrolysis of ATP.

Summary Table: Key Thermodynamic Concepts in Biology

Additional info: These notes expand on the transcript by providing definitions, equations, and examples for key thermodynamic and metabolic concepts relevant to General Biology. The tables and equations are inferred from standard biology curricula and the context of the lecture.