Energy, Enzymes, and Metabolism: Core Concepts in General Biology

Energy, Enzymes, and Metabolism

Energy Basics

Energy is a fundamental concept in biology, essential for all cellular processes and life functions. Understanding the forms and laws governing energy helps explain how organisms maintain order and carry out metabolism.

• Energy: The capacity to do work, move, or elicit change.

• Enthalpy (H): Internal system energy, including heat content.

• Potential Energy: Stored energy due to location or chemical structure (e.g., chemical bonds, gradients).

• Kinetic Energy: Energy of motion (e.g., heat, molecular movement).

• Thermal Energy: A type of kinetic energy responsible for temperature; heat is the flow of thermal energy.

First Law of Thermodynamics

Energy cannot be created or destroyed, only converted from one form to another.

• Example: Chemical energy in food is converted to kinetic energy for movement.

Second Law of Thermodynamics

Energy will always become more spread out and disordered (entropy increases); energy flows from high to low, center to out.

• Entropy (S): Measure of disorder/randomness; increases in spontaneous processes.

• Example: Living organisms maintain order by using energy (e.g., ATP).

Energy Dispersion

• Molecule motion increases in system

• More volume

• More number

• More molecular motion

Gibbs Free Energy (G)

Portion of a system's energy that is available to do work (convertible energy).

• Change in Free Energy (ΔG): Determines if a reaction is spontaneous.

ΔG Value	Reaction Type	Description
ΔG < 0	Exergonic	Spontaneous, releases energy
ΔG > 0	Endergonic	Requires energy input, non-spontaneous

• Exergonic Reaction: Releases energy, occurs spontaneously.

• Endergonic Reaction: Requires energy input, not spontaneous.

ATP & Metabolism

ATP (adenosine triphosphate) is the universal energy currency in cells, coupling exergonic and endergonic reactions to power cellular processes.

• Structure of ATP: Adenine + ribose + 3 phosphate groups.

• Role of ATP: Couples energy-releasing and energy-requiring reactions.

ATP Hydrolysis

• Reactants: ATP + H2O

• Products: ADP + Pi (inorganic phosphate) + energy released

• Equation: $ext{ATP} + ext{H}_2 ext{O} ightarrow ext{ADP} + ext{P}_i + ext{energy}$

• Exergonic: Used to power cellular processes.

Anabolism and Catabolism

• Anabolism (Anabolic Pathways): Build complex molecules; require energy (endergonic).

• Catabolism (Catabolic Pathways): Break down complex molecules into simpler compounds; release energy (exergonic).

Enzymes & Reaction Rates

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy, without being consumed in the process.

• Role of Enzymes: Lower activation energy, speed reactions, do not change ΔG.

• Activation Energy (Ea): Minimum energy required to start a reaction (reach transition state). $ext{Ea}$

• How Enzymes Work: Substrates bind to the enzyme's active site, stabilizing the transition state and facilitating product release.

• Induced Fit: Enzyme changes shape slightly to better fit substrate.

Mechanisms of Enzyme Action

1. Binds to substrates at active site

2. Promotes substrates reaching transition state

3. Releases products as products have less affinity for active site

Factors Affecting Enzyme Activity

• Temperature: Too high = denaturation; too low = slowed activity.

• pH: Extreme pH alters enzyme structure and function.

• Concentration of Substrate/Enzyme: More substrate = faster reaction until saturation; more enzyme = higher rate.

• Presence of Cofactors/Coenzymes: Required for proper activity.

• Inhibitors/Regulators: Competitive, non-competitive, allosteric regulation.

Enzyme Regulation

Enzyme activity is tightly regulated to ensure metabolic balance and efficiency. Regulation can occur through inhibitors, feedback mechanisms, and protein modifications.

• Competitive Inhibition: Substrate and inhibitor compete for active site; can be overcome by more substrate.

• Non-Competitive Inhibition: Inhibitor binds allosterically; lowers activity regardless of substrate amount.

• Feedback Inhibition: End product shuts down pathway at an early step (prevents waste, regulates balance).

• Protein Modifications: Phosphorylation or cleavage can activate/deactivate enzymes.

• Control Points: Usually the first enzyme in a pathway is regulated (prevents waste).

• Pathways in Evolution: Pathways arose early in life and continue to adapt in cells.

Key Terms & Definitions

Term	Definition
Enthalpy (H)	Total energy in a system (includes heat content).
Entropy (S)	Measure of disorder/randomness; increases in spontaneous processes.
Free Energy (G)	Energy available to do work.
Change in Free Energy (ΔG)	Determines if a reaction is spontaneous.
Exergonic Reaction	Releases energy, occurs spontaneously.
Endergonic Reaction	Requires energy input, not spontaneous.
Activation Energy (Ea)	Minimum energy required to start a reaction.
Substrate	Reactant molecule that binds to an enzyme's active site.
Active Site	Region on enzyme where substrate binds and reaction occurs.
Catalysis	Acceleration of a reaction by lowering activation energy.
Cofactor	Non-protein helper (often metal ions) required for enzyme function.
Coenzyme	Organic helper molecule (e.g., NAD+, FAD, vitamins).
Prosthetic Group	Non-protein molecule tightly bound to enzyme, aiding function.
Enzyme Inhibitor	Molecule that decreases enzyme activity.
Competitive Inhibitor	Binds to active site, blocking substrate.
Non-competitive Inhibitor	Binds elsewhere (allosteric site), changing enzyme shape and reducing function.

Examples & Applications

• ATP Hydrolysis: Powers muscle contraction, active transport, and biosynthesis.

• Enzyme Regulation: Feedback inhibition in glycolysis prevents excess ATP production.

• Competitive Inhibition: Drugs like penicillin inhibit bacterial enzymes by competing for active sites.

Additional info: Some context and definitions were expanded for clarity and completeness, including examples and equations for ATP hydrolysis and enzyme regulation.