Carbon – The Framework of Biological Molecules

Section 3.1: Carbon – The Framework of Biological Molecules Key Concepts: Carbon as the Backbone of Life: Carbon atoms form the framework of biological molecules due to their ability to form four covalent bonds. Carbon can bond with other carbon atoms or with atoms like hydrogen, oxygen, nitrogen, sulfur, and phosphorus. This allows for the formation of straight chains, branches, rings, and complex structures like balls, tubes, and coils. Hydrocarbons: Molecules consisting only of carbon and hydrogen (e.g., propane, C₃H₈). Hydrocarbons are nonpolar and release energy when oxidized, making them good fuels. Functional Groups: Functional groups are specific groups of atoms that give molecules their chemical properties. Common functional groups include: Hydroxyl (-OH): Polar, found in alcohols. Carbonyl (C=O): Polar, found in aldehydes and ketones. Carboxyl (-COOH): Acidic, found in amino acids and fatty acids. Amino (-NH₂): Basic, found in amino acids. Phosphate (-PO₄⁻): Found in nucleic acids and ATP. Functional groups determine the polarity, solubility, and reactivity of molecules. Isomers: Structural Isomers: Same molecular formula but different structures (e.g., glucose and fructose). Stereoisomers: Same carbon skeleton but different spatial arrangements (e.g., D-glucose and L-glucose). Enantiomers: Mirror-image stereoisomers (e.g., D-sugars and L-amino acids). Biological Macromolecules: Carbohydrates: Energy storage and structural molecules. Nucleic Acids: Information storage and transfer (DNA, RNA). Proteins: Diverse functions, including catalysis and structure. Lipids: Hydrophobic molecules, including fats and membranes. Polymerization: Dehydration Reactions: Monomers are linked by removing water (H₂O). Hydrolysis Reactions: Polymers are broken down by adding water. Section 3.2: Carbohydrates – Energy Storage and Structural Molecules Key Concepts: Monosaccharides: Simple sugars with 3-7 carbon atoms (e.g., glucose, fructose, galactose). Glucose (C₆H₁₂O₆) is the most important energy-storing sugar. Monosaccharides can form ring structures in aqueous solutions. Isomers and Stereoisomers: Glucose, Fructose, and Galactose are isomers with the same formula (C₆H₁₂O₆) but different structures. α-glucose and β-glucose differ in the orientation of the -OH group on carbon 1. Disaccharides: Formed by linking two monosaccharides via glycosidic bonds. Examples: Sucrose (glucose + fructose): Table sugar. Lactose (glucose + galactose): Milk sugar. Maltose (glucose + glucose): Found in grains. Polysaccharides: Long chains of monosaccharides used for energy storage and structural support. Starch (α-glucose): Energy storage in plants. Amylose: Unbranched chains. Amylopectin: Branched chains. Glycogen (α-glucose): Energy storage in animals, highly branched. Cellulose (β-glucose): Structural support in plant cell walls. β-(1→4) glycosidic bonds make cellulose resistant to digestion. Chitin: Structural support in arthropods and fungi, made of N-acetylglucosamine. Section 3.3: Nucleic Acids – Information Molecules Key Concepts: Nucleotides: Building blocks of nucleic acids (DNA and RNA). Each nucleotide consists of: A 5-carbon sugar (ribose in RNA, deoxyribose in DNA). A phosphate group. A nitrogenous base (A, T, C, G in DNA; A, U, C, G in RNA). DNA Structure: Double helix with two antiparallel strands. Base-pairing rules: A-T (or A-U in RNA) and C-G. Hydrogen bonds between bases stabilize the double helix. RNA Structure: Usually single-stranded. Contains ribose and uracil instead of thymine. Types of RNA: mRNA: Carries genetic information from DNA. tRNA: Transfers amino acids during protein synthesis. rRNA: Component of ribosomes. Functions of Nucleic Acids: DNA: Stores genetic information. RNA: Involved in protein synthesis, gene regulation, and enzymatic functions. Other Nucleotides: ATP: Energy currency of the cell. NAD+ and FAD: Electron carriers in cellular respiration. Section 3.4: Proteins – Molecules with Diverse Structures and Functions Key Concepts: Amino Acids: Proteins are polymers of 20 different amino acids. Each amino acid has: An amino group (-NH₂). A carboxyl group (-COOH). A unique R group (side chain) that determines its properties. Protein Structure: Primary Structure: Sequence of amino acids. Secondary Structure: Local folding into α-helices and β-sheets via hydrogen bonds. Tertiary Structure: Overall 3D shape of a single polypeptide chain, stabilized by: Hydrogen bonds. Ionic bonds. Disulfide bridges (covalent bonds between cysteine residues). Hydrophobic interactions. Quaternary Structure: Association of multiple polypeptide chains (e.g., hemoglobin). Motifs and Domains: Motifs: Recurring structural elements (e.g., β-α-β motif, helix-turn-helix). Domains: Functional units within a protein that perform specific tasks. Protein Folding: Chaperone Proteins: Assist in proper folding (e.g., GroE in E. coli). Heat Shock Proteins: Help refold proteins under stress. Denaturation and Renaturation: Denaturation: Loss of protein structure due to changes in pH, temperature, or ionic concentration. Renaturation: Refolding of a protein into its native structure. Protein Functions: Enzymes: Catalyze biochemical reactions. Structural Proteins: Provide support (e.g., collagen, keratin). Transport Proteins: Carry molecules (e.g., hemoglobin). Signaling Proteins: Transmit signals (e.g., hormones). Section 3.5: Lipids – Hydrophobic Molecules Key Concepts: Fats and Oils: Triglycerides: Composed of 1 glycerol and 3 fatty acids. Saturated Fats: No double bonds, solid at room temperature (e.g., animal fats). Unsaturated Fats: One or more double bonds, liquid at room temperature (e.g., plant oils). Trans Fats: Synthetic, unhealthy fats. Phospholipids: Composed of 1 glycerol, 2 fatty acids, and 1 phosphate group. Form phospholipid bilayers in cell membranes. Polar heads face outward, nonpolar tails face inward. Other Lipids: Steroids: Hormones (e.g., cholesterol, estrogen). Prostaglandins: Signaling molecules. Lipid Aggregates: Micelles: Spherical structures with polar heads outward. Lipid Bilayers: Found in cell membranes. Summary Tables: Macromolecules Overview: Macromolecule Subunits Functions Examples Carbohydrates Monosaccharides Energy storage, structure Glucose, starch, cellulose Nucleic Acids Nucleotides Information storage DNA, RNA Proteins Amino acids Catalysis, structure Enzymes, hemoglobin Lipids Fatty acids, glycerol Energy storage, membranes Triglycerides, phospholipids Protein Structure Levels: Level Description Primary Sequence of amino acids Secondary Local folding (α-helices, β-sheets) Tertiary Overall 3D shape of a single polypeptide chain Quaternary Association of multiple polypeptide chains Key Takeaways: Carbon is the backbone of all biological molecules. Functional groups determine the properties of organic molecules. Isomers have the same formula but different structures, leading to different functions. Macromolecules (carbohydrates, nucleic acids, proteins, lipids) are essential for life. Protein structure is hierarchical, and proper folding is crucial for function. Lipids are hydrophobic and play key roles in energy storage and membrane formation.