Biochemistry — Comprehensive Study Notes Summary & Study Notes

🧬 Overview

Biochemistry studies the chemical processes in living systems. Focus on the structures, functions, and interactions of biomolecules and the pathways that transform energy and matter in cells.

🧪 Major Biomolecules

Proteins, carbohydrates, lipids, and nucleic acids are the four major classes. Each has distinct monomers, bonds, and cellular roles.

🧩 Proteins & Amino Acids

Amino acids are the building blocks; they link via peptide bonds to form polypeptides. Key properties derive from side chains: polar, nonpolar, acidic, and basic. Protein structure levels: primary (sequence), secondary (α-helix, β-sheet), tertiary (3D fold), quaternary (multi-subunit).

🍞 Carbohydrates

Monosaccharides (glucose, fructose) form disaccharides and polysaccharides by glycosidic bonds. Storage forms: glycogen (animals) and starch (plants). Cellulose provides structural support; humans lack cellulase.

🧈 Lipids & Membranes

Fatty acids, triglycerides, and phospholipids are key lipids. Phospholipid bilayers form cell membranes; membrane fluidity influenced by temperature, saturation, and cholesterol. Membranes host transporters and signaling proteins.

🧪 Nucleic Acids & Genetic Information

DNA stores genetic information (double helix of deoxyribonucleotides); RNA (ribonucleotides) is involved in expression and regulation. Central dogma: DNA → RNA → Protein (replication, transcription, translation).

⚡ Energy Currency & Redox

ATP is the primary energy currency. Reducing equivalents: NADH, NADPH, FADH2. Important small molecules: $ATP$, $ADP$, $AMP$, $NAD^+$, $NADH$, $FAD$, $FADH_2$.

🔁 Core Metabolic Pathways

• Glycolysis: glucose → pyruvate, yields ATP and NADH.
• Pyruvate dehydrogenase: pyruvate → acetyl-CoA.
• TCA cycle: acetyl-CoA oxidation produces NADH, FADH2, and $CO_2$.
• Oxidative phosphorylation: electron transport chain creates proton gradient to drive ATP synthesis. Approximate yields: glycolysis + TCA + oxidative phosphorylation yield tens of ATP per glucose depending on shuttle and conditions.

🧮 Enzyme Kinetics & Catalysis

Enzymes lower activation energy and increase reaction rates. Key concepts: active site, specificity, cofactors, and coenzymes. Michaelis–Menten equation: $v = \frac{V_{max}[S]}{K_m + [S]}$. $K_m$ reflects substrate affinity; $V_{max}$ is maximal velocity. Types of inhibition: competitive, noncompetitive, uncompetitive.

🧪 Thermodynamics & Bioenergetics

Cellular reactions follow thermodynamic rules: ΔG determines spontaneity. Coupling unfavorable reactions to ATP hydrolysis often makes processes favorable. Understand standard ΔG'° vs cellular conditions.

🧫 Membrane Transport & Bioenergetics

Transport types: passive diffusion, facilitated diffusion, active transport (primary uses ATP, secondary uses gradients). Proton gradients drive ATP synthesis via ATP synthase.

🧬 Signal Transduction & Regulation

Cells use receptors, second messengers (e.g., $cAMP$, Ca^{2+}), and phosphorylation cascades to regulate metabolism and gene expression. Feedback inhibition is common in metabolic control.

🧾 Acid-Base Chemistry & Buffers

pH affects enzyme activity and ionization states. Henderson–Hasselbalch equation: $pH = pK_a + \log \frac{[A^-]}{[HA]}$. Physiological pH is tightly regulated (blood ~7.4).

🧪 Vitamins & Cofactors

Many vitamins are precursors for coenzymes (e.g., niacin → NAD^+, riboflavin → FAD). Deficiencies impair enzyme-catalyzed reactions.

🔬 Common Lab Techniques

Key methods: chromatography (separation), electrophoresis (size/charge), mass spectrometry (mass/identification), spectrophotometry (concentration, kinetics), and western blot / PCR for proteins and nucleic acids.

✅ Practical Study Tips

Focus on mechanisms (how and why), memorize key pathways and regulation points (e.g., rate-limiting enzymes), and practice pathway mapping. Use one-letter amino acid codes and group properties for quick recall.

📚 Quick Reference Lists

• Essential amino acids: PVT TIM HALL mnemonic.
• Hydrophobic amino acids: A, V, L, I, M, F, W, Y.
• Key metabolites: glucose, pyruvate, acetyl-CoA, citrate, oxaloacetate, ATP, NADH.

🧭 Final Notes

Link structure to function: molecular details explain cellular behavior. Start with core pathways (glycolysis, TCA, ETS), then layer regulation, signaling, and specialized pathways (lipid metabolism, amino acid catabolism). Keep diagrams and reaction sequences concise for revision.