Energy, Thermodynamics, and Metabolism in Biological Systems

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This section reviews recent assessment results and provides strategies for mastering course material in General Biology.

Quiz 2: Average score was 70.7%, with a top score of 100% (8 students).
Exam 1: Average score was 63.6%, with a top score of 100% (3 students).
Suggested Study Approach:
- Read eText chapters before lectures.
- Complete Dynamic Study Modules after lectures and before assignments.
- Attend office hours and review quizzes/discussion sections for clarification.

Energy is essential for all biological processes, enabling organisms to perform work and maintain order.

Energy: The capacity to cause change, especially to do work (move matter against opposing forces).
Kinetic Energy: Energy of motion; includes heat (thermal energy), which is the kinetic energy of randomly moving molecules.
Potential Energy: Stored energy due to position or structure; can be released to do work.
Chemical Energy: A form of potential energy stored in chemical bonds, released during chemical reactions.
Example: Glucose contains chemical energy that cells can extract during cellular respiration.

Thermodynamics explains how energy is transferred and transformed in biological systems.

System: The matter under study; everything outside is the surroundings.
Isolated System: Cannot exchange energy or matter with surroundings (rare in biology).
Open System: Can exchange energy and matter with surroundings; living organisms are open systems.

The first law, also known as the law of conservation of energy, states:

Energy cannot be created or destroyed, only transformed or transferred.
During energy transfer, some energy is lost as heat.
Equation: (where is heat and is work; not always explicitly used in biology, but underlies all energy changes).

The second law states that every energy transfer increases the entropy (disorder) of the universe.

Entropy (S): A measure of molecular disorder or randomness.
Energy transformations are never 100% efficient; some energy is always lost as heat, increasing entropy.
Living systems maintain order locally by increasing entropy in their surroundings.
Example: Cellular respiration releases heat, increasing the entropy of the environment.

Metabolism encompasses all chemical reactions occurring in a living organism.

Catabolic Pathways: Break down complex molecules into simpler ones, releasing energy (e.g., cellular respiration).
Anabolic Pathways: Build complex molecules from simpler ones, consuming energy (e.g., protein synthesis).
Metabolic pathways are tightly regulated and interconnected.

Chemical reactions in cells are governed by the laws of thermodynamics and tend toward equilibrium.

Law of Conservation of Mass: Atoms are neither created nor destroyed in chemical reactions.
Dynamic Equilibrium: Forward and reverse reactions occur at the same rate; concentrations of reactants and products remain constant.
Le Châtelier's Principle: If a system at equilibrium is disturbed, it will shift to restore equilibrium.
In living cells, metabolic pathways are not allowed to reach equilibrium; this allows for continuous flow of materials and energy.

Gibbs free energy is the portion of a system's energy that can perform work at constant temperature and pressure.

Change in Free Energy (): Determines whether a reaction is spontaneous.
Equation:
Where:
- = Change in enthalpy (total energy)
- = Absolute temperature in Kelvin
- = Change in entropy
Spontaneous Reactions: Occur without input of energy ().
Nonspontaneous Reactions: Require energy input ().
Example: Cellular respiration is highly spontaneous with kcal/mol.

The actual free energy change depends on the concentrations of reactants and products.

Equation:
Where:
- = Standard free energy change (under standard conditions)
- = Ideal gas constant (8.314 J/mol·K)
- = Temperature in Kelvin
- = Reaction quotient (ratio of product to reactant concentrations)
Interpretation: If , reaction favors products; if , reaction favors reactants.

The pH scale measures the concentration of hydrogen ions () in a solution, which is critical for biological processes.

A small number of chemical groups determine the properties and functions of biological molecules.

Functional Groups: Specific groups of atoms within molecules that have characteristic properties and chemical reactivity.
Examples include hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl groups.
Importance: Recognizing these groups is essential for understanding molecular function in biology.

Concept	Definition	Biological Example
First Law of Thermodynamics	Energy cannot be created or destroyed, only transformed or transferred	Conversion of chemical energy in glucose to ATP
Second Law of Thermodynamics	Every energy transfer increases the entropy of the universe	Heat released during muscle contraction
Gibbs Free Energy ()	Energy available to do work	Spontaneity of cellular respiration
pH	Measure of hydrogen ion concentration	Enzyme activity dependence on pH

Some content (e.g., specific chemical group structures) was referenced but not detailed; students should refer to their textbook for Figure 4.9 and memorize the structures and properties of functional groups.
Equations and thermodynamic relationships are foundational for understanding metabolism and energy flow in cells.