Metabolism and Energy Transformation

Observation of bioluminescence when swimming in water at night, particularly produced by dinoflagellates.
Bioluminescence: A process where energy from the food consumed is transformed into light energy by organisms like dinoflagellates.

Definition of Metabolism: In biological systems, metabolism refers primarily to metabolic pathways.
Metabolic Pathways Explained:
- Represent the sequence of steps that alter a specific molecule into another product.
- Frequently discussed in the context of biochemistry.
Example Pathway:
- Starting with molecule A, like glucose, it undergoes a series of transformations to finally produce cellulose.
- Not instantaneous; involves distinct steps:
- Transformation Steps:
  - Step 1: Glucose modified by an enzyme to a different form.
  - Step 2: Glucose monomers linked by another enzyme.
  - Final assembly into a complex structure (e.g., cellulose).

Reactions can run in two directions:
- Catabolic Reactions: Break down large molecules, e.g., breaking sugar into smaller molecules.
- Anabolic Reactions: Build larger, more complex molecules from smaller, simpler starting materials.
- Association with anabolic steroids, which promote muscle growth (anabolic refers to building).

Importance of Physics: Biological systems obey the laws of physics and chemistry.
Understanding energy types is crucial:
- Kinetic Energy: Related to movement; higher movement correlates with higher kinetic energy.
- Potential Energy: Associated with an object's position; e.g., a person at a height on a diving board has potential energy.
Energy Transformation Example:
- Jumping from a diving board converts potential energy to kinetic energy.

Chemical Energy: Stored in bonds (e.g., in ATP's last phosphate bond).
Thermal Energy: A type of kinetic energy, associated with molecular movement.

First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.
- Example: Drinking water transforms that water matter into energy.
Second Law of Thermodynamics: Entropy increases with energy transformations.
- Entropy Definition: A measure of disorder; e.g., a shattered glass has higher entropy than an intact glass.
- Energy transformations result in increased universe disorder, exemplified in metabolic processes like digestion.

Chemical reactions that increase entropy typically occur without energy input (spontaneous reactions).
Spontaneous Reaction Example: Water flowing over a waterfall requires no energy to happen.
Non-Spontaneous Reaction Example: Water humping back up requires energy investment.

Definition: Proportion of energy available to do work in a system, particularly in metabolic pathways.
Formula: Change in free energy defined as $ext{ΔG} = G<em>{ ext{products}} - G</em>{ ext{reactants}}$
- If $ext{ΔG} ext{ is positive}$ , energy is absorbed (non-spontaneous).
- If $ext{ΔG} ext{ is negative}$ , energy is released (exergonic, spontaneous).
Conceptual connection to stability in free energy:
- Molecules with high free energy are usually unstable, while lower free energy indicates a stable state.

Exergonic Reactions: Release energy; typically spontaneous (e.g., cellular respiration).
Endergonic Reactions: Absorb energy; not spontaneous (e.g., photosynthesis).
Further breakdown of energy transitions:
- Example: Cellular respiration involves the breakdown of glucose (high free energy) into CO2 and water (low free energy), releasing energy.
Example: Photosynthesis is the reverse process, using sunlight to convert CO2 and water into glucose, thus requiring energy.

Equilibrium Concept: The forward and reverse chemical reactions occur at the same rate, indicating no net change in concentration of reactants or products.
A system at equilibrium has minimal free energy, hence no energy available for work.
Living cells are never at equilibrium; they constantly exchange materials and energy with the environment.

ATP (Adenosine Triphosphate): Key energy currency of the cell; used to power three types of work:
- Chemical Work: Driving non-spontaneous reactions (endergonic).
- Transport Work: Moving substances against a concentration gradient.
- Mechanical Work: Moving structures in the cell (e.g., cilia, flagella).
Energy Coupling: Utilize the energy released from exergonic reactions to drive endergonic reactions using ATP.
Hydrolysis of ATP: Breaking down ATP into ADP and inorganic phosphate to release energy; only the terminal phosphate is involved in this reaction, not the other two.

Phosphorylation Process: ATP adds a phosphate group to a substrate (reactant), increasing its free energy and instability, promoting the reaction.
Example of Glutamic Acid Reaction: Conversion of glutamic acid and ammonia to glutamine:
- Without ATP, this reaction has a positive ΔG (endergonic).
- With ATP, phosphorylation allows it to become exergonic.
Combined ΔG Calculation: Adding ΔG of glutamic acid reaction (3.4) and ΔG from ATP hydrolysis (-7.3) results in negative ΔG (-3.9), making the overall reaction spontaneous.

Enzymes: Proteins that catalyze reactions, speeding up metabolic pathways without being consumed.
Activation Energy: Minimum energy required for reactants to overcome in order to form products. Enzymes lower this energy threshold.
Mechanisms of Regulation:
- Competitive Inhibition: An inhibitor molecule competes with the substrate for the active site.
- Allosteric Regulation: An inhibitor changes the enzyme's shape and active site conformation, preventing substrate binding.
- Feedback Inhibition: The end product of a pathway inhibits an earlier enzyme, regulating the pathway's activity.

Understanding metabolic pathways, thermodynamics, free energy, and enzymatic regulation is crucial for grasping how biological functions break down and build up molecules essential for life.