Chapter 8: An Introduction to Metabolism – Study Notes

Learning Objectives

• Identify the first two laws of thermodynamics and explain how they relate to biological systems.

• Explain what is meant by change in free energy and relate it to spontaneous reactions, capacity to do work, stability, and exergonic and endergonic reactions.

• Use examples to illustrate the coupling of ATP hydrolysis to endergonic reactions.

• Explain how enzymes speed up metabolic reactions.

• Describe how regulation of enzyme activity helps control metabolism.

Thermodynamics and Biological Processes

The First and Second Laws of Thermodynamics

Thermodynamics describes how energy is transferred and transformed in biological systems. These laws are fundamental to understanding metabolism and energy flow in living organisms.

• First Law of Thermodynamics: Energy can be transferred or transformed, but not created or destroyed. This is also known as the principle of conservation of energy.

• Second Law of Thermodynamics: Every energy transfer or transformation increases the entropy (disorder) of the universe. Some energy is always lost as heat, making it unavailable to do work.

• Entropy: A measure of molecular disorder or randomness. As entropy increases, systems become less ordered and less energy is available for useful work.

Example: Light energy from the sun is transformed by plants into chemical energy, which is then transferred to other organisms (e.g., termites). Each transformation releases heat, increasing entropy.

Concept 8.1: Metabolism Transforms Matter and Energy

Definition and Emergent Properties

Metabolism is the totality of an organism’s chemical reactions. It is an emergent property of life arising from orderly interactions between molecules.

Metabolic Pathways

Metabolic pathways are sequences of chemical reactions, each catalyzed by a specific enzyme, that convert a starting molecule into a product.

• Enzyme: A macromolecule that speeds up a specific reaction.

• Each step in a pathway is facilitated by a different enzyme.

Example: The breakdown of glucose in cellular respiration involves multiple steps, each catalyzed by a different enzyme.

Types of Metabolic Pathways

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

  • Example: Cellular respiration (breakdown of glucose in the presence of oxygen).

  • Analogy: "Downhill" reactions because they release energy.

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

  • Example: Protein synthesis (forming proteins from amino acids).

  • Analogy: "Uphill" reactions because they require an input of energy.

Forms of Energy

Kinetic and Potential Energy

Energy is the capacity to cause change and can be used to do work, such as moving matter against opposing forces.

• Kinetic Energy: Energy associated with motion. Moving objects can perform work by imparting motion to other matter (e.g., water turning turbines).

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

• Heat: The transfer of thermal energy from one body of matter to another.

• Light: A form of energy that can be harnessed to do work, such as in photosynthesis.

• Potential Energy: Energy that matter possesses because of its location or structure (e.g., water behind a dam).

• Chemical Energy: Potential energy available for release in a chemical reaction. Complex molecules like glucose are high in chemical energy.

The Laws of Energy Transformation

Thermodynamics

Thermodynamics is the study of energy transformations within a collection of matter.

• Isolated System: Cannot exchange energy or matter with its surroundings (e.g., liquid in a thermos bottle).

• Open System: Can exchange energy and matter with its surroundings. Living organisms are open systems, absorbing energy from light or food and releasing heat and metabolic wastes (e.g., CO2).

Table: Comparison of Catabolic and Anabolic Pathways

Pathway Type	Energy Flow	Example	Analogy
Catabolic	Releases energy	Cellular respiration	Downhill
Anabolic	Consumes energy	Protein synthesis	Uphill

Key Terms and Definitions

• Metabolism: All chemical reactions in an organism.

• Enzyme: Protein that speeds up chemical reactions.

• Catabolic Pathway: Breaks down molecules, releases energy.

• Anabolic Pathway: Builds molecules, consumes energy.

• Kinetic Energy: Energy of motion.

• Potential Energy: Stored energy due to position or structure.

• Chemical Energy: Potential energy in chemical bonds.

• Thermodynamics: Study of energy transformations.

• Isolated System: No exchange with surroundings.

• Open System: Exchanges energy and matter with surroundings.

• Entropy: Measure of disorder.

Additional info: Later sections of the chapter (not shown in these images) would cover free energy, ATP coupling, and enzyme regulation in more detail.