Biochemistry Exam 1 Review: Chapters 1-4 Study Guide

Chemistry is Logic of Biological Phenomena

Distinguishing Properties of Living Systems

Biochemistry explores the chemical principles underlying living organisms. Understanding the unique features of life is foundational for studying biological molecules and processes.

• Distinctive Properties: Living systems exhibit organization, metabolism, growth, response to stimuli, and reproduction.

• Cell Structure and Function: Cells are the basic units of life, with prokaryotic cells lacking a nucleus and eukaryotic cells possessing membrane-bound organelles.

• Biological Hierarchy: Life is organized from molecules to cells, tissues, organs, and organisms.

• Organization and Structure: The cell is the fundamental unit; prokaryotes (e.g., Escherichia coli) have simpler organization than eukaryotes (e.g., human cells).

• Weak vs. Strong Forces: Biological interactions rely on both strong covalent bonds and weak noncovalent forces (hydrogen bonds, ionic interactions, van der Waals forces, hydrophobic effect).

• Bond Energies: Covalent bonds are stronger and provide stability; noncovalent interactions allow dynamic biological processes.

• Homeostasis: Enzymes and hormones regulate internal conditions to maintain stability.

• Macromolecules: Carbohydrates, lipids, nucleic acids, and proteins are the major classes. Each has unique monomers and polymers.

• Structure and Function: The structure of biomolecules determines their function (e.g., enzyme active sites, DNA double helix).

• Examples: Glucose (carbohydrate), triglycerides (lipid), DNA/RNA (nucleic acids), hemoglobin (protein).

Water: The Medium of Life

Properties and Biological Importance of Water

Water is essential for life, serving as a solvent, reactant, and temperature buffer. Its unique properties arise from its molecular structure and hydrogen bonding.

• Hydrogen Bonding: Water molecules form hydrogen bonds, leading to high cohesion, surface tension, and specific heat.

• Solvent Properties: Water dissolves polar and ionic substances, facilitating biochemical reactions.

• Interactions: Water interacts with other molecules via hydrogen bonds and dipole interactions.

• Ionization: Water can ionize to form H+ and OH-, affecting pH.

• pH and Buffers: pH measures hydrogen ion concentration; buffers maintain pH stability in biological systems.

• Electrolytes: Substances that dissociate in water to produce ions, important for nerve and muscle function.

• Henderson-Hasselbalch Equation: Relates pH, pKa, and ratio of acid/base forms: $pH = pK_a + \log\left(\frac{[A^-]}{[HA]}\right)$

• Biological Buffers: Examples include phosphate and bicarbonate buffers in blood.

• Example: Water's role in hydrolysis reactions and maintaining cellular pH.

Thermodynamics of Biological Systems

Basic Concepts and Applications

Thermodynamics governs energy transformations in biological systems, determining the direction and spontaneity of biochemical reactions.

• Key Concepts: System, surroundings, energy, enthalpy (H), entropy (S), and free energy (G).

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

• Second Law: Entropy of the universe increases in spontaneous processes.

• Standard State and Free Energy: Standard free energy change ($\Delta G^\circ$) predicts reaction spontaneity. $\Delta G = \Delta H - T\Delta S$

• Gibbs Free Energy: Negative $\Delta G$ indicates a spontaneous reaction.

• Thermodynamics in Biology: Coupled reactions, ATP hydrolysis, and metabolic pathways.

• Example: ATP hydrolysis drives endergonic cellular processes.

Amino Acids and the Peptide Bond

Structure, Properties, and Classification

Amino acids are the building blocks of proteins. Their structure and properties determine protein function and diversity.

• Standard Amino Acids: 20 naturally occurring amino acids, each with a unique side chain (R group).

• One-Letter and Three-Letter Codes: Used for shorthand notation (e.g., Gly for glycine, G).

• Structural Formula: General structure: $\mathrm{NH_2{-}CHR{-}COOH}$

• Categories: Amino acids are classified as nonpolar, polar uncharged, acidic, or basic.

• Polypeptide Formation: Amino acids link via peptide bonds (amide linkage) to form proteins.

• Peptide Bond: Formed by condensation reaction between amino and carboxyl groups. $\mathrm{Amino~acid_1{-}COOH} + \mathrm{Amino~acid_2{-}NH_2} \rightarrow \mathrm{Peptide~bond} + H_2O$

• Stereochemistry: Most amino acids are chiral (except glycine); L-form is predominant in proteins.

• Ionization: Amino acids can exist as zwitterions at physiological pH.

• Chromatography and HPLC: Techniques for separating and analyzing amino acids and proteins based on chemical properties.

• Example: Glutamic acid (acidic), lysine (basic), serine (polar uncharged), valine (nonpolar).

Table: Classification of Amino Acids

Category	Examples	Properties
Nonpolar (Hydrophobic)	Glycine, Alanine, Valine, Leucine, Isoleucine	Hydrophobic side chains, found in protein interiors
Polar Uncharged	Serine, Threonine, Asparagine, Glutamine	Hydrophilic, form hydrogen bonds
Acidic	Aspartic acid, Glutamic acid	Negatively charged at physiological pH
Basic	Lysine, Arginine, Histidine	Positively charged at physiological pH

Additional info:

• Chromatography (including HPLC) is essential for protein purification and analysis in biochemistry.

• Peptide bonds have partial double-bond character, restricting rotation and influencing protein structure.