Energy, Thermodynamics, and Enzyme Function in General Biology

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Energy and Thermodynamics

Energy Basics

Energy is the capacity to do work, move, or elicit change in biological systems. It exists in various forms and is fundamental to all living processes.

Energy: The ability to do work, move, or cause change.
Enthalpy (H): The total internal energy of a system, 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 a flow of thermal energy.

First Law of Thermodynamics

The first law states that 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

The second law states that energy will always become more spread out and disordered (entropy increases). Energy flows from high to low concentration.

Entropy (S): A measure of disorder/randomness; increases in spontaneous processes.
How does energy disperse?
1. Molecule motion increases in system
2. More volume
3. More number
4. More molecular motion

Gibbs Free Energy (G)

Gibbs free energy is the portion of a system's energy available to do work. It determines if a reaction is spontaneous.

Change in Free Energy (ΔG): Indicates spontaneity of a reaction.
: Exergonic, spontaneous (releases energy)
: Endergonic, non-spontaneous (requires energy input)

Exergonic and Endergonic Reactions

Exergonic Reaction: Releases energy, occurs spontaneously.
Endergonic Reaction: Requires energy input, not spontaneous.

ATP and Metabolism

Structure and Role of ATP

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

Structure of ATP: Adenine + ribose + 3 phosphate groups.
Role of ATP: Couples energy-releasing and energy-consuming reactions.

ATP Hydrolysis

Reactants: ATP + H2O
Products: ADP + Pi (inorganic phosphate) + energy released
Equation:
Exergonic: Used to power cellular processes.

Anabolism and Catabolism

Anabolic Pathways: Build complex molecules; require energy (endergonic).
Catabolic Pathways: Break down complex molecules into simpler compounds; release energy (exergonic).
Example: Breakdown of glucose in cellular respiration (catabolic, exergonic).

Enzymes and Reaction Rates

Role and Mechanism of Enzymes

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

Enzymes: Proteins catalyzing chemical reactions; increase rate, lower activation energy.
Activation Energy (Ea): Minimum energy required to start a reaction.
How Enzymes Work: Substrates bind to the enzyme's active site, stabilizing the transition state and releasing products.
Induced Fit: Enzyme changes shape slightly to better fit the substrate.

Mechanisms of Enzyme Action

Binds to substrates at active site
Promotes substrate reaching transition state
Releases products as products have less affinity for active site

Factors Affecting Enzyme Activity

Temperature: Too high can denature enzyme; too low slows 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

Types of Inhibition

Competitive Inhibition: Inhibitor competes 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 to prevent waste and regulate balance.

Protein Modifications

Phosphorylation or cleavage can activate/deactivate enzymes.
Protein modification changes shape and activity of proteins (e.g., unphosphorylated form is inactive, phosphorylated form is active).

Control Points and Pathways in Evolution

Control Points: Usually the first enzyme in a pathway is regulated to prevent 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 (reach transition state).
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.

Summary Table: Exergonic vs. Endergonic Reactions

Type of Reaction	ΔG	Energy Flow	Spontaneity
Exergonic		Releases energy	Spontaneous
Endergonic		Requires energy input	Non-spontaneous

Additional info: Some context and definitions were expanded for clarity and completeness, including the structure and function of ATP, mechanisms of enzyme action, and regulatory processes in metabolism.