Metabolism: Transforming Matter and Energy

Metabolic Pathways

Metabolism refers to the sum total of all chemical reactions occurring within an organism. These reactions are organized into metabolic pathways, where a specific molecule is transformed through a series of steps, each catalyzed by a unique enzyme, resulting in a final product.

• Metabolic Pathway Example: A starting molecule (A) is converted to molecule B by Enzyme 1, then to molecule C by Enzyme 2, and finally to product D by Enzyme 3.

• Enzyme Regulation: Enzymes are regulated to balance supply and demand, similar to how traffic lights control flow.

• Metabolism's Role: Manages the cell's material and energy resources.

Types of Metabolic Pathways

• Catabolic Pathways: Break down complex molecules into simpler ones, releasing energy. Example: Cellular respiration breaks down glucose to carbon dioxide and water.

• Anabolic Pathways: Build complex molecules from simpler ones, consuming energy. Example: Synthesis of proteins from amino acids.

• Relationship: Energy released from catabolic ("downhill") reactions can be used to drive anabolic ("uphill") reactions.

Bioenergetics is the study of how energy flows through living organisms.

Forms of Energy

Energy Definitions and Types

Energy is the capacity to cause change or do work, such as moving matter against forces like gravity or friction. Cells transform energy from one form to another to perform life processes.

• Kinetic Energy: Energy associated with the motion of objects. Example: Water flowing through a dam turns turbines.

• Thermal Energy: Kinetic energy from random movement of atoms or molecules. When transferred, it is called heat.

• Light Energy: Electromagnetic energy used in processes like photosynthesis.

• Potential Energy: Energy stored due to an object's position or structure. Example: Water behind a dam, or energy in chemical bonds.

• Chemical Energy: Potential energy available for release in a chemical reaction. Example: Glucose is high in chemical energy.

Energy Transformation Example

• A person climbing a ladder uses chemical energy from food, converting it to kinetic energy (muscle movement), then to potential energy (height).

• Diving converts potential energy to kinetic energy, which is transferred to water, causing splashing and heat.

Organisms are energy transformers: Plants convert light energy to chemical energy; animals convert chemical energy to kinetic and thermal energy.

The Laws of Energy Transformation (Thermodynamics)

Systems and Surroundings

In thermodynamics, a system is the matter under study, and the surroundings are everything else. Systems can be:

• Isolated: No exchange of energy or matter (e.g., liquid in a thermos).

• Open: Exchange energy and matter with surroundings (e.g., living organisms).

The First Law of Thermodynamics

The first law states that energy can be transferred and transformed, but not created or destroyed. This is the principle of conservation of energy.

• Plants transform sunlight to chemical energy; animals transform chemical energy to kinetic and thermal energy.

Equation:

The Second Law of Thermodynamics

The second law states that every energy transfer or transformation increases the disorder (entropy) of the universe. Some energy is always lost as heat, making it unavailable for work.

• Entropy (S): A measure of molecular disorder or randomness. The more random, the higher the entropy.

• Spontaneous processes increase entropy and occur without energy input (may be fast or slow).

• Nonspontaneous processes decrease entropy and require energy input.

Equation:

(for spontaneous processes)

For a process to occur spontaneously, it must increase the entropy of the universe.

Biological Order and Disorder

Order in Living Systems

Cells and organisms create ordered structures from less organized materials, but overall, they increase the entropy of their surroundings.

• Example: Amino acids are assembled into proteins; animals break down food into CO2 and H2O, releasing heat.

• Energy flows into ecosystems as light and exits as heat.

• Organisms are "islands" of low entropy in a universe trending toward higher entropy.

Order in Nature and Architecture

• The Venus flower basket sponge has a highly ordered structure, inspiring architectural designs like the towers of La Sagrada Familia.

The evolution of biological order does not violate the second law; local decreases in entropy are offset by increases in the surroundings.

Concept Check: Applications

Diffusion and Entropy

The second law of thermodynamics explains diffusion: substances move from areas of higher concentration to lower concentration, increasing entropy.

Energy in an Apple

• Growing on a tree: Apple stores chemical energy (potential energy) from photosynthesis.

• Falling: Potential energy is converted to kinetic energy as it falls.

• Digested: Chemical energy is released during metabolism, used for cellular work, and some is lost as heat.

Summary Table: Types of Energy and Examples

Additional info: The notes expand on the original content by providing definitions, examples, and equations for clarity and completeness. The summary table is inferred for study purposes.