Chapter 1: Biochemistry and the Language of Chemistry

1.1 Origins of Life

The origins of life are explored through theories such as the primordial atmosphere theory, which describes how simple molecules gave rise to complex biological systems.

• Abiogenesis: The process by which life arises naturally from non-living matter. Major elements in biological compounds include carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.

• Miller-Urey Experiment: Demonstrated that amino acids and other organic molecules could be synthesized from simple gases under early Earth conditions.

• Functional Groups: Common groups include hydroxyl, carboxyl, amino, phosphate, and sulfhydryl, which determine the chemical properties of biomolecules.

• Condensation and Hydrolysis: Condensation reactions join molecules by removing water; hydrolysis breaks bonds by adding water.

• Self-Replicating Systems: Early life forms evolved mechanisms for replication, relying on molecular complementarity and compartmentation (formation of cell-like structures).

• Seven Pillars of Life: Organization, metabolism, energy, homeostasis, growth, adaptation, and reproduction characterize living systems.

1.2 Cellular Architecture

Cellular architecture describes the evolution and structure of cells, distinguishing prokaryotes from eukaryotes and identifying organelle functions.

• Evolution from Unicellular Organisms: Energy utilization drives natural selection and complexity.

• Prokaryotes vs. Eukaryotes: Prokaryotes lack membrane-bound organelles; eukaryotes possess nucleus, mitochondria, ER, Golgi, etc.

• Cellular Organelles: Each organelle has specialized functions, e.g., mitochondria (energy), ribosomes (protein synthesis), lysosomes (degradation).

Chapter 2: Chemical Foundation of Life - Water

2.1 Physical Properties of Water

Water's unique properties stem from its molecular structure and ability to form hydrogen bonds, making it essential for life.

• Molecular Structure: Water is bent with a bond angle of ~104.5°, bond distance ~0.96 Å. Deviations arise from lone pair repulsion.

• Hydrogen Bonds: Water molecules form extensive hydrogen bonds, affecting density (ice is less dense than liquid water).

• Intermolecular Forces: Hydrogen bonds are stronger than van der Waals but weaker than covalent bonds.

• Solvent Function: Water dissolves ions by forming hydration shells; polar compounds are hydrophilic, non-polar are hydrophobic.

• Hydrophobic Effect: Drives self-organization of biomolecules (e.g., membrane formation).

• Amphipathic Molecules: Contain both hydrophilic and hydrophobic regions; form micelles or bilayers in water.

• Dialysis: Separation of solutes by diffusion across a semi-permeable membrane; clinically used to remove waste from blood.

2.2 Ionization and pH

Water ionizes to form H+ and OH-, and its ionization constant (Kw) is fundamental to acid-base chemistry.

• Ionization Constant: at 25°C

• pH Calculation:

• Strong vs. Weak Acids/Bases: Strong acids/bases fully dissociate; weak acids/bases partially dissociate.

• Henderson-Hasselbalch Equation:

• Buffer: A solution that resists changes in pH; blood uses the carbonic acid-bicarbonate system.

• Blood Buffering: Carbonic acid-bicarbonate system responds to pH changes by shifting equilibrium.

Chapter 4: Nucleic Acids

4.1 Nucleotides

Nucleotides are the monomers of nucleic acids, consisting of a phosphate, pentose sugar, and nitrogenous base.

• Nucleoside: Sugar + base; Nucleotide: Sugar + base + phosphate.

• Nitrogenous Bases: Purines (A, G), Pyrimidines (C, T, U).

• Base Pairing: A pairs with T (or U in RNA), C pairs with G; A=T (2 H-bonds), C≡G (3 H-bonds).

• Sugar Attachment: Purines attach at N9, pyrimidines at N1.

4.2 Nucleic Acid Structure

Nucleic acids are polymers of nucleotides linked by phosphodiester bonds, forming DNA and RNA.

• Phosphodiester Bond: Links 3' and 5' carbons of sugars.

• Sequence Reading: Always 5' to 3'.

• DNA Structure: Double helix, antiparallel strands, discovered by Watson and Crick, supported by Chargaff's rule and Franklin's X-ray data.

• RNA: Single-stranded, contains ribose and uracil; can form secondary structures.

4.3 Nucleic Acid Function

DNA stores genetic information, replicates, and is transcribed and translated according to the Central Dogma.

• Replication: DNA is copied by enzymes (helicase, topoisomerase, ligase, polymerase).

• Denaturation/Annealing: Denaturation separates strands; annealing re-forms double helix.

• PCR: Polymerase Chain Reaction amplifies DNA using template, primers, dNTPs, Taq polymerase; involves thermal cycling.

• Central Dogma: DNA → RNA → Protein.

• Transcription: DNA is transcribed to mRNA; Translation: mRNA is translated to protein using tRNA and ribosomes.

Chapter 5: Introduction to Proteins

5.1 Amino Acids: Building Blocks

Amino acids are the monomers of proteins, classified by their side chain properties.

• Structure: Central α-carbon, amino group, carboxyl group, side chain (R).

• Zwitterion: Molecule with both positive and negative charges at neutral pH.

• Classification: Nonpolar, polar uncharged, polar charged (positive/negative), hydrophobic/hydrophilic, aromatic/aliphatic.

• Abbreviations: 3-letter and 1-letter codes for each amino acid.

• Disulfide Bonds: Covalent bonds between cysteine residues; stabilize protein structure.

• pK Values: Used to determine ionization and net charge of amino acids and peptides.

• Isoelectric Point (pI): pH at which a molecule carries no net charge.

• Peptide Formation: Amino acids join via peptide bonds.

5.2 Stereochemistry

Amino acids (except glycine) are chiral, existing as L- or D- forms; proteins use L-amino acids.

• Chiral Center: α-carbon is chiral.

• Fischer Projection: Used to distinguish L- and D- forms.

• Significance: Stereochemistry affects protein structure and function.

5.3 Amino Acid Derivatives

Some amino acids are modified to form derivatives with specialized functions.

• Glutathione: Tripeptide (Glu-Cys-Gly); functions as an antioxidant.

• Antioxidant Function: Reduces oxidative stress via redox reactions.

5.4 Polypeptide Diversity

Proteins exhibit diversity in sequence and structure, determined by amino acid composition.

• Primary Structure: Linear sequence of amino acids.

• Sequence Possibilities: for a peptide of n residues.

• Abundant/Rare Amino Acids: Some amino acids are more common in proteins.

• Surface/Interior Occurrence: Nonpolar residues are interior; polar/charged are surface.

5.5 Protein Purification

Proteins are purified and quantified using various assays and spectroscopic methods.

• Assays: ELISA, colorimetric, and spectrophotometric assays (aromatic residues absorb UV 200-400 nm).

• Stability Factors: Temperature, pH, proteases, and chemical properties affect protein stability.

• Purification Strategies: Use size, charge, hydrophobicity, and affinity for separation.

5.6 Protein Sequencing

Protein sequencing involves chemical and enzymatic cleavage followed by analysis of fragments.

• Reagents: Dansyl chloride (N-terminal), 2-mercaptoethanol (reduces disulfide), iodoacetate (alkylates cysteine), Edman degradation (sequential removal).

• Chemical Cleavage: Cyanogen bromide (CNBr) cleaves at methionine.

• Enzymatic Cleavage: Trypsin (Lys/Arg), chymotrypsin (aromatic), elastase (small), V8 (Glu).

• Sequence Determination: Analyze fragments to reconstruct sequence.

5.7 Protein Evolution

Protein evolution is studied by comparing sequences and constructing phylogenetic trees.

• Residue Types: Invariant (unchanged), conservatively substituted (similar properties), hypervariable (rapidly changing).

• Phylogenetic Trees: Visualize evolutionary relationships based on sequence similarity.

Chapter 6: Proteins - Three-Dimensional Structure

6.1 Secondary Structure

Secondary structure refers to local folding patterns in proteins, stabilized by hydrogen bonds.

• Peptide Bond: Rigid, planar due to resonance; usually trans configuration.

• Ramachandran Diagram: Shows allowed phi (φ) and psi (ψ) angles; steric hindrance limits conformations (glycine and proline are exceptions).

• Alpha Helix: Right-handed, 3.6 residues/turn, pitch 5.4 Å; side chains project outward.

• Beta Sheet: Strands can be parallel or antiparallel (antiparallel more stable); repeat distance ~7 Å.

• Protein Shape: Fibrous (structural, e.g., keratin, collagen) vs. globular (functional, e.g., enzymes).

• Keratin: Coiled coil, 7-residue pseudorepeat, nonpolar at positions a and d; found in hair, nails.

• Collagen: Triple helix, rich in Gly, Pro, Hydroxyproline; left-handed helix, high tensile strength.

6.2 Tertiary Structure

Tertiary structure is the overall 3D arrangement of a protein, determined by interactions among side chains.

• Determination: X-ray crystallography and NMR spectroscopy.

• Spatial Arrangement: Nonpolar residues interior, charged residues surface, uncharged can be either.

• Supersecondary Structure/Motifs: Combinations of secondary structures (e.g., β-barrel, α-helix bundle).

• Protein Domains: Independently folding units (~100-200 residues).

• Evolutionary Conservation: Structure is often conserved even as sequence changes.

6.3 Quaternary Structure

Quaternary structure describes the assembly of multiple polypeptide chains into a functional protein complex.

• Definition: Association of two or more polypeptide chains (subunits).

Additional info: This study guide covers foundational biochemistry topics relevant for exam preparation, including origins of life, water chemistry, nucleic acids, amino acids, and protein structure. For each topic, students should be able to define terms, explain processes, and apply concepts to biological systems.