Biochemistry and the Language of Chemistry

Origins and Scope of Biochemistry

Biochemistry is the study of the chemical processes and substances that occur within living organisms. It bridges biology and chemistry, focusing on the molecular mechanisms underlying life.

• Friederich Wöhler: Demonstrated the synthesis of urea from inorganic compounds, disproving vitalism and marking the birth of biochemistry as a scientific discipline.

• Eduard and Hans Buchner: Showed that cell-free extracts could ferment sugar, proving that biochemical reactions can occur outside living cells.

• CHNOPS: The six most common elements in biological molecules: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur.

• RNA World Hypothesis: Proposes that self-replicating RNA molecules were precursors to current life, highlighting the central role of nucleic acids in early evolution.

• Biopolymer: Large molecules composed of repeating subunits (e.g., proteins, nucleic acids, polysaccharides).

Major Classes of Biological Molecules

• Proteins: Polymers of amino acids; perform catalysis, structure, signaling, and transport.

• Nucleic Acids: DNA and RNA; store and transmit genetic information.

• Carbohydrates: Sugars and polysaccharides; provide energy and structural support.

• Lipids: Hydrophobic molecules; form membranes and store energy.

Seven Pillars of Life (Daniel Koshland)

Koshland's principles distinguish living from nonliving systems:

• Program: Genetic instructions (DNA/RNA).

• Improvisation: Ability to change over generations (evolution).

• Compartmentalization: Separation of internal environment (cells, organelles).

• Energy: Harnessing and using energy for work.

• Regeneration: Repair and maintenance.

• Adaptability: Responding to environmental changes.

• Seclusion: Specificity of biochemical pathways.

Cellular Organization

• Prokaryotes: Lack membrane-bound organelles; DNA in nucleoid region (e.g., Escherichia coli).

• Eukaryotes: Have nucleus and organelles (e.g., mitochondria, ER); compartmentalized functions.

Modern Biochemical Fields

• Bioinformatics: Computational analysis of biological data (e.g., genome sequences).

• Proteomics: Study of the entire set of proteins in a cell or organism.

• Metabolomics: Comprehensive analysis of metabolites in a biological system.

• Synthetic Biology: Engineering new biological parts or systems.

Key Techniques

• DNA Microarray: Measures gene expression levels across thousands of genes simultaneously.

• 2-D Electrophoresis: Separates proteins based on isoelectric point and molecular weight.

The Chemical Foundation of Life: Weak Interactions in an Aqueous Environment

Chemical Bonds and Interactions

Biological molecules interact through a variety of chemical bonds and forces, which determine structure and function.

• Covalent Bonds: Strong bonds formed by sharing electrons.

• Noncovalent Interactions: Weaker, reversible interactions crucial for biological processes:

  • Electrostatic (Ionic) Interactions: Attraction between charged groups (e.g., salt bridges).

  • Hydrogen Bonds: Attraction between a hydrogen atom bonded to an electronegative atom (O or N) and another electronegative atom.

  • Van der Waals Forces: Weak, transient interactions due to fluctuating electron distributions.

  • Hydrophobic Effect: Nonpolar molecules aggregate in water to minimize disruption of hydrogen-bonded water network.

• Bond Energies: Covalent bonds (~200–400 kJ/mol) are much stronger than noncovalent interactions (1–40 kJ/mol).

Properties of Water

• Polarity: Water is a polar molecule with a bent structure, leading to a dipole moment (μ).

• Hydrogen Bonding: Each water molecule can form up to four hydrogen bonds, giving water a high heat capacity and heat of vaporization.

• Solvent Properties: Water dissolves ionic and hydrophilic molecules but excludes hydrophobic molecules, leading to the formation of clathrates and the hydrophobic effect.

• Amphipathic Molecules: Contain both hydrophilic and hydrophobic regions (e.g., phospholipids).

Acids, Bases, and Buffers

• Acid: Proton donor; Base: Proton acceptor.

• Conjugate Acid/Base: Pair differing by one proton.

• pH:

• pKa: (acid dissociation constant)

• Henderson-Hasselbalch Equation:

• Buffer: Solution that resists changes in pH upon addition of acid or base; important for maintaining physiological pH.

• Titration: Used to determine the concentration of an acid or base in solution.

Electrophoresis and Isoelectric Focusing

• Electrophoresis: Separation of charged molecules in an electric field; used for DNA, RNA, and proteins.

• Isoelectric Focusing: Separates proteins based on their isoelectric point (pI), the pH at which the molecule has no net charge.

Solubility of Biomolecules

• pH and Ionic Strength: Affect solubility and charge state of biomolecules.

• Macroions: Large charged molecules (e.g., proteins, nucleic acids) whose solubility depends on pH, ionic strength, and their own charge properties.

The Energetics of Life

Thermodynamics in Biological Systems

Thermodynamics describes the flow and transformation of energy in biological systems, determining whether reactions are favorable.

• System vs. Surroundings: The system is the part of the universe under study; everything else is the surroundings.

• Types of Systems:

  • Open: Exchanges matter and energy with surroundings (e.g., living cells).

  • Closed: Exchanges energy but not matter.

  • Isolated: Exchanges neither energy nor matter.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Second Law of Thermodynamics: The entropy (disorder) of the universe tends to increase; spontaneous processes increase total entropy.

Enthalpy, Entropy, and Free Energy

• Enthalpy (H): Heat content of a system.

• Entropy (S): Measure of disorder or randomness.

• Gibbs Free Energy (G): Determines spontaneity of a process.

• Exergonic: ; process is spontaneous.

• Endergonic: ; process is non-spontaneous.

• At Equilibrium:

Equilibrium and Reaction Direction

• Equilibrium Constant (K): Ratio of product to reactant concentrations at equilibrium.

• Reaction Quotient (Q): Same ratio at any point; comparing Q to K predicts direction of reaction.

• Standard Free Energy Change (): Free energy change under standard conditions (1 M, 1 atm, 25°C).

• Biochemical Standard State (): Standard free energy at pH 7.0, relevant for biological systems.

Coupling Reactions and ATP Hydrolysis

• Coupling: Unfavorable reactions () can proceed by coupling to favorable ones (), such as ATP hydrolysis.

• ATP Structure: Contains phosphoanhydride ("high-energy") and phosphoester bonds.

• Hydrolysis of ATP: Releases energy to drive cellular processes.

Redox Reactions and Reduction Potential

• Reduction Potential (E): Tendency of a molecule to accept electrons; important for electron transport and metabolism.

Dynamic and Reversible Interactions

• Biological systems are dynamic; directionality depends on free energy and concentrations of reactants/products.

• Enzymes accelerate reactions by lowering activation energy but do not change equilibrium position.

Equilibrium vs. Homeostasis

• Equilibrium: No net change in concentrations; .

• Homeostasis: Maintenance of stable internal conditions, often far from equilibrium, via regulatory mechanisms.

Example: ATP hydrolysis is highly exergonic and is used to drive many endergonic cellular reactions, such as muscle contraction and active transport.

Additional info: The equations and concepts above are foundational for understanding metabolism, enzyme function, and cellular regulation in biochemistry.