Sources and References

Primary texts — Nelson, D.L. and Cox, M.M., Lehninger Principles of Biochemistry, 8th ed., Macmillan, 2021; Alberts, B. et al., Molecular Biology of the Cell, 7th ed., Garland Science, 2022.

Supplementary texts — Shuler, M.L., Kargi, F., and DeLisa, M., Bioprocess Engineering: Basic Concepts, 3rd ed., Prentice Hall, 2017; Voet, D., Voet, J.G., and Pratt, C.W., Fundamentals of Biochemistry, 5th ed., Wiley, 2016.

Online resources — MIT OCW 7.01SC “Fundamentals of Biology” and 20.110J “Thermodynamics of Biomolecular Systems”; Harvard Molecular and Cellular Biology open materials; NCBI Bookshelf (Molecular Biology of the Cell, Biochemistry by Berg); UniProt and Protein Data Bank; KEGG pathway maps.

Chapter 1: The Chemical Basis of Life

1.1 Water and Buffered Solutions

Life runs in water. Water’s polarity, hydrogen-bonding network, high heat capacity, high heat of vaporization, and unusual solid-phase density underwrite cellular chemistry. The autoionization of water, \( K_w = [H^+][OH^-] = 10^{-14} \) at 25 °C, defines pH = \( -\log_{10}[H^+] \).

The Henderson-Hasselbalch equation

describes buffered mixtures. Physiological buffers—bicarbonate in blood, phosphate and histidine within cells—maintain pH in the 7.2–7.4 range; deviations of even 0.3 units threaten life.

1.2 Functional Groups and Organic Chemistry Review

Hydroxyl, carbonyl, carboxyl, amino, phosphate, sulfhydryl, and amide groups confer distinctive reactivity. Key reactions:

• Condensation: two monomers join, releasing water (peptide bond formation, glycosidic linkage).
• Hydrolysis: water cleaves a bond (digestion, ATP hydrolysis).
• Oxidation-reduction: electron transfer underlies metabolism.
• Phosphorylation and its reverse: key regulatory switches.

1.3 Weak Interactions

Covalent bonds carry tens to hundreds of kJ/mol; weak interactions—hydrogen bonds (5–30 kJ/mol), van der Waals (\( \sim 1 \) kJ/mol), ionic interactions in water, and the hydrophobic effect—do most of the work of biology. Their weakness is their virtue: they form and break reversibly at room temperature, enabling regulation, recognition, and dynamics.

Chapter 2: Biomolecules

2.1 Amino Acids and Proteins

Twenty standard amino acids share an \( \alpha \)-carbon bonded to H, NH\(_2\), COOH, and a variable side chain. Side chains are nonpolar (Ala, Val, Leu, Ile, Met, Phe, Trp), polar uncharged (Ser, Thr, Cys, Asn, Gln, Tyr), positively charged (Lys, Arg, His), or negatively charged (Asp, Glu). Glycine (no side chain) and proline (cyclic) break patterns.

Peptide bonds link amino acids into polypeptides. Protein structure has four levels:

• Primary — amino acid sequence.
• Secondary — local hydrogen-bonded patterns (α-helix, β-sheet, turns).
• Tertiary — full 3D fold of one chain.
• Quaternary — assembly of multiple chains.

Proteins catalyze (enzymes), transport (hemoglobin, membrane pumps), signal (receptors, hormones), provide structure (collagen, actin), defend (antibodies), and regulate (transcription factors).

2.2 Nucleic Acids

DNA and RNA are polymers of nucleotides (base + sugar + phosphate). DNA stores genetic information as a double helix; RNA transcribes and translates it. Base-pairing rules: A=T (A=U in RNA), G≡C. The central dogma—DNA → RNA → protein—governs information flow, with exceptions (reverse transcription, RNA replication, prions) illustrating biology’s refusal to conform to simple rules.

2.3 Carbohydrates

Monosaccharides (glucose, fructose, ribose) assemble into disaccharides (sucrose, lactose) and polysaccharides (starch, glycogen, cellulose). Energy storage (starch in plants, glycogen in animals), structure (cellulose in plants, chitin in arthropods), and recognition (glycoproteins) are their roles. Stereochemistry matters: cellulose and starch differ only in the anomeric \( \alpha/\beta \) linkage, yet one we digest and the other we cannot.

2.4 Lipids

Lipids are defined by solubility (nonpolar) rather than a common scaffold: fatty acids, triglycerides, phospholipids, sterols, terpenes. The phospholipid bilayer self-assembles from amphiphiles driven by the hydrophobic effect; its fluid-mosaic structure hosts the membrane proteins that govern cellular transport and signaling.

Chapter 3: Enzymes and Kinetics

3.1 Enzyme Catalysis

Enzymes are (usually) proteins that accelerate specific reactions by \( 10^5 \) to \( 10^{17} \)-fold without being consumed. Mechanisms: proximity and orientation, general acid-base catalysis, covalent catalysis, and metal ion catalysis. The active site binds substrate(s) with geometric and chemical complementarity.

3.2 Michaelis-Menten Kinetics

For the simple mechanism

the steady-state assumption yields

where \( K_M \) is the substrate concentration at half \( V_{max} \). Lineweaver-Burk plots (\( 1/v \) vs \( 1/[S] \)) linearize the equation for parameter estimation, though nonlinear regression is statistically preferred.

3.3 Inhibition and Regulation

Competitive inhibitors raise apparent \( K_M \); uncompetitive inhibitors lower both \( K_M \) and \( V_{max} \); noncompetitive inhibitors lower \( V_{max} \) only. Allosteric enzymes display sigmoidal kinetics described by the Hill equation; feedback inhibition by end-products regulates pathways.

Chapter 4: Cells and Metabolism

4.1 Cell Structure

Prokaryotes (bacteria, archaea) lack nuclei and membrane-bound organelles; eukaryotes (protists, fungi, plants, animals) have both. Key eukaryotic organelles: nucleus (DNA), mitochondria (ATP via oxidative phosphorylation), endoplasmic reticulum (protein and lipid synthesis), Golgi apparatus (post-translational processing), lysosomes (degradation), peroxisomes (oxidation). Plant cells add chloroplasts (photosynthesis), cell walls, and large vacuoles.

4.2 Central Metabolism

ATP (\( \Delta G \approx -30 \) kJ/mol for hydrolysis at cellular conditions) is the universal energy currency. Cells produce ATP through:

• Glycolysis — 10 steps converting glucose to pyruvate; net 2 ATP, 2 NADH per glucose.
• Pyruvate oxidation and the citric acid (Krebs) cycle — 2 ATP (GTP), 8 NADH, 2 FADH\(_2\) per glucose, plus 6 CO\(_2\).
• Oxidative phosphorylation — the electron transport chain uses NADH and FADH\(_2\) to pump protons across the inner mitochondrial membrane; ATP synthase harnesses the proton gradient to produce ATP (\( \sim 30 \) ATP/glucose total).

Photosynthesis reverses combustion: CO\(_2\) + H\(_2\)O + light → glucose + O\(_2\), with chlorophyll-based light reactions and the Calvin cycle fixing carbon.

4.3 Biosynthesis

Anabolic pathways build macromolecules from simple precursors, consuming ATP and reducing equivalents. Central metabolic intermediates (acetyl-CoA, \( \alpha \)-ketoglutarate, oxaloacetate, ribose-5-phosphate) feed biosynthesis of amino acids, nucleotides, fatty acids, and cofactors.

4.4 Regulation

Hormonal signals, enzyme covalent modification (phosphorylation/dephosphorylation), and allosteric control tune flux. Metabolic control analysis quantifies which enzymes exert the most control over a pathway’s output—rarely a single rate-limiting step in reality.

Chapter 5: From Genes to Systems

5.1 Replication, Transcription, Translation

DNA replication is semiconservative, with DNA polymerase extending in the 5’ → 3’ direction using a template strand. Transcription by RNA polymerase produces mRNA; eukaryotic mRNAs are spliced, capped, and polyadenylated. Translation at the ribosome reads codons and links amino acids via tRNAs charged with aminoacyl groups. The genetic code is redundant (61 sense codons for 20 amino acids) and nearly universal.

5.2 Gene Regulation

In bacteria, operons (lac, trp) illustrate transcriptional control. In eukaryotes, regulation integrates transcription factors, chromatin modifications, non-coding RNAs, and post-translational modification. The result: a single genome encodes hundreds of cell types via differential expression.

5.3 Recombinant DNA and Genetic Engineering

Restriction enzymes, DNA ligase, PCR, DNA sequencing (Sanger, Illumina, nanopore), and CRISPR-Cas9 editing form the molecular biologist’s toolbox. Heterologous expression in E. coli or yeast produces therapeutic proteins (insulin, growth hormone, monoclonal antibodies).

5.4 Omics and Systems Biology

Genomics sequences genomes. Transcriptomics measures all mRNAs (RNA-seq). Proteomics identifies and quantifies proteins (mass spectrometry). Metabolomics profiles small molecules (NMR, LC-MS). Systems biology integrates these with kinetic models, flux balance analysis, and genome-scale models to predict cellular behavior.

Chapter 6: Engineering Applications

6.1 Biomimetic Design

Nature solves engineering problems over geologic timescales: gecko adhesion inspired dry-adhesive tapes; lotus-leaf superhydrophobicity inspired self-cleaning surfaces; spider silk informs high-strength fibers; photosynthesis motivates artificial leaves. Biomimetic design draws functional principles rather than literal copies.

6.2 Bioprocess and Biocatalysis

Industrial fermentation produces antibiotics, amino acids, organic acids, enzymes, and biofuels. Biocatalysis uses isolated enzymes for stereospecific synthesis (esterases for chiral drugs, nitrile hydratases for acrylamide). Metabolic engineering rewires host organisms for products not in their native repertoire.

6.3 Biomaterials and Therapeutics

Drug delivery vehicles (liposomes, polymer nanoparticles, antibody-drug conjugates), tissue engineering scaffolds, and biosensors all draw on biological design. mRNA vaccines demonstrated the power of synthetic biology delivered at pandemic scale.