This chapter explores the fundamental building blocks of living organisms, moving from simple inorganic molecules to the complex organic structures that form the architecture of the cell.
All matter in the universe is composed of atoms, but in biology, we categorize the resulting compounds based on their chemical complexity and the presence of carbon.
Inorganic compounds are generally simple, small, and lack carbon-hydrogen (C-H) bonds. Although some contain carbon (like carbon dioxide, \(CO_2\)) or hydrogen (like water, \(H_2O\)), they do not contain both. * Examples: Water, mineral salts (e.g., \(NaCl\)), acids, bases, and gases like \(O_2\) and \(CO_2\). * Biological Role: They serve as solvents, reactants in metabolic pathways, and structural components (e.g., calcium phosphate in bones).
Organic compounds are defined by the presence of carbon atoms covalently bonded to hydrogen. Carbon’s ability to form four stable covalent bonds allows it to build complex, diverse “backbones” for life. * The Four Classes: Carbohydrates, Lipids, Proteins, and Nucleic Acids. * Properties: They are often large macromolecules (polymers) built from smaller repeating units (monomers) through dehydration synthesis (removal of water to form a bond).
[Figure 1: Comparison of Compounds] Description: A two-part diagram. On the left, simple inorganic molecules like \(H_2O\) and \(NaCl\) (ionic lattice). On the right, a complex organic molecule like Glucose (\(C_6H_{12}O_6\)) highlighting the C-C and C-H covalent backbone.
Carbohydrates are composed of Carbon, Hydrogen, and Oxygen, typically in a 1:2:1 ratio (\(CH_2O)_n\). They are categorized by the number of sugar units they contain.
These are the monomers (single units) of carbohydrates. They typically contain 3 to 7 carbons. * Glucose (\(C_6H_{12}O_6\)): The primary energy source for cellular respiration. It exists as a straight chain or a more stable ring structure in aqueous solutions. * Fructose & Galactose: Isomers of glucose (same formula, different arrangement), found in fruits and milk. * Ribose & Deoxyribose: 5-carbon sugars (pentoses) that form the backbone of RNA and DNA.
Formed when two monosaccharides join via a glycosidic bond through a condensation reaction. * Sucrose (Table Sugar): Glucose + Fructose. * Lactose (Milk Sugar): Glucose + Galactose. * Maltose (Malt Sugar): Glucose + Glucose.
Long chains of hundreds or thousands of monosaccharides. 1. Storage Polysaccharides: * Starch: Glucose storage in plants (found in seeds and tubers). * Glycogen: Glucose storage in animals (highly branched, stored in liver and muscle). 2. Structural Polysaccharides: * Cellulose: Forms the rigid cell wall of plants. Humans cannot digest it (fiber). * Chitin: Found in the exoskeletons of insects and the cell walls of fungi.
[Figure 2: Carbohydrate Structures] Description: A series of three diagrams: (1) A hexagonal glucose ring. (2) Two glucose rings joined by an oxygen bridge (glycosidic bond) to form maltose. (3) A long, branched chain of glucose units representing glycogen.
Lipids are a diverse group of non-polar molecules that do not dissolve in water. * Triglycerides (Fats and Oils): Composed of one glycerol and three fatty acids. * Saturated: No double bonds; straight chains pack tightly (solid at room temp, like butter). * Unsaturated: One or more double bonds create “kinks”; cannot pack tightly (liquid, like olive oil). * Phospholipids: Composed of glycerol, two fatty acids (hydrophobic tails), and a phosphate group (hydrophilic head). These are the fundamental components of cell membranes. * Steroids: Composed of four fused carbon rings (e.g., Cholesterol, Testosterone).
Proteins are polymers of amino acids joined by peptide bonds. There are 20 different amino acids, each with a unique “R-group” (side chain).
[Figure 3: Protein Folding] Description: A flow diagram showing (1) a bead-like chain for primary structure, (2) a spiral ribbon for alpha-helix, (3) a globule for tertiary, and (4) four intertwined globules for quaternary structure.
Water is polar because oxygen is more electronegative than hydrogen, creating partial charges (\(\delta-\) on O, \(\delta+\) on H). This leads to hydrogen bonding.
Enzymes are usually proteins that speed up chemical reactions by lowering the activation energy.
[Figure 4: Enzyme Inhibition] Description: Two panels. Panel A shows a “wrong” molecule blocking the active site (Competitive). Panel B shows a molecule binding to the side of the enzyme, causing the active site to collapse (Non-competitive).
The membrane is described by the Fluid Mosaic Model. It is “fluid” because molecules move laterally, and “mosaic” because it is a mixture of various components.
[Figure 5: The Fluid Mosaic Model] Description: A cross-section of the membrane showing a bilayer of “heads and tails.” Large blue protein “icebergs” are embedded. Cholesterol yellow rings are between tails, and green sugar chains sprout from the top surface like antennae.