A weak electrostatic attraction between a hydrogen atom bonded to N, O, or F and another N, O, or F atom. Individual H-bonds are weak (~5% of covalent bond), but collectively they give water its unique properties

The oxygen atom has a stronger electronegativity than hydrogen, creating a polar covalent bond with partial charges (delta- on O, delta+ on H). This polarity makes water an excellent solvent ("universal solvent")

Water molecules attract each other via hydrogen bonding. Causes surface tension (water "beads" on surfaces) and allows water to travel up xylem vessels in plants against gravity

Water molecules attract molecules of other substances. Enables capillary action - water "climbs" up narrow tubes due to adhesion to walls plus cohesion between water molecules

The measure of how difficult it is to break the surface of a liquid. Result of cohesion; water has unusually high surface tension due to hydrogen bonding. Allows small organisms (e.g., water striders) to walk on water

Water requires a large amount of energy to change temperature. The hydrogen bonding network absorbs heat without a large temperature change. Helps stabilize environmental temperatures and cellular conditions

The combined effect of cohesion and adhesion. Water rises in narrow spaces (e.g., plant xylem, paper towels) because adhesive forces pull water up walls while cohesive forces hold the column together

• Carbon Skeletons: The carbon backbone of organic molecules. Can be straight chain, branched, or ring-shaped. Carbon forms 4 covalent bonds, allowing immense molecular diversity. Chains can vary in length, degree of saturation, and functional group attachments

The six essential elements of life (CHNOPS). Carbon (structural backbone), Hydrogen (in all organic molecules), Oxygen (in carbohydrates, lipids), Nitrogen (in proteins, nucleic acids), Phosphorus (in DNA, ATP, phospholipids), Sulfur (in some amino acids: cysteine, methionine). Trace elements (Fe, I, Se, Zn) are required in small amounts

A reaction that builds macromolecules by removing a water molecule to form a covalent bond between monomers. Occurs in the rough ER and Golgi for proteins; in cytoplasm for carbohydrates. Reversible - requires energy (ATP)

The reverse of dehydration synthesis. Breaks covalent bonds by adding a water molecule. Digests polymers into monomers. Occurs in lysosomes, digestive system, and cellular processes requiring monomer release

Monomers are single subunit molecules that repeat to form polymers. The four major biological macromolecules: carbohydrates (monosaccharides), proteins (amino acids), lipids (fatty acids + glycerol), nucleic acids (nucleotides). Assembly: monomers -> dehydration synthesis -> polymers

Simple sugars (single sugar unit). General formula: (CH2O)n where n = 3-7. Key examples: glucose (C6H12O6, main energy currency), fructose, galactose. Can form disaccharides (e.g., sucrose = glucose + fructose) via glycosidic linkages

Lipids are composed mainly of C and H (nonpolar) and are therefore hydrophobic ("water-fearing"). They do not dissolve in water. This property drives the formation of cell membranes (phospholipid bilayer). Includes triglycerides, phospholipids, steroids, waxes

Saturated fatty acids have no C=C double bonds (straight chain -> pack tightly -> solid at room temperature, e.g., butter). Unsaturated fatty acids have one or more C=C double bonds (kinked chain -> cannot pack tightly -> liquid at room temperature, e.g., olive oil). Trans fats are artificially hydrogenated unsaturated fats

DNA: double-stranded, deoxyribose sugar, thymine (T), genetic storage, stable. RNA: single-stranded (usually), ribose sugar, uracil (U) instead of thymine, involved in gene expression. DNA is antiparallel; RNA is typically linear

Purines (A, G): double-ring structures (9-membered). Pyrimidines (C, T, U): single-ring structures (6-membered). In DNA: A pairs with T (2 H-bonds), G pairs with C (3 H-bonds). Chargaff's rules: [A] = [T] and [G] = [C]

Each nucleotide has a 5' carbon (phosphate group) and a 3' carbon (hydroxyl group). The sugar-phosphate backbone runs 5' -> 3' direction. The two strands of DNA run antiparallel - one strand 5' -> 3', the other 3' -> 5'. This directionality is essential for DNA replication and transcription

The two strands of DNA run in opposite directions. One strand runs 5' -> 3' and the complementary strand runs 3' -> 5'. Each end of a DNA double helix has one 5' phosphate end and one 3' hydroxyl end. Essential for DNA polymerase to function during replication

The 20 amino acids differ by their R-group (side chain). R-groups determine properties: nonpolar/hydrophobic, polar uncharged, electrically charged (acidic or basic). Amino acids are linked by peptide bonds (formed via dehydration synthesis)

The linear sequence of amino acids in a polypeptide chain. Determined by the gene's DNA sequence. Any change (mutation) in this sequence can affect protein function. The primary structure dictates all higher-level structures

Local folding patterns stabilized by hydrogen bonds between backbone C=O and N-H groups. Alpha helix: right-handed coil; common in structural proteins (keratin, collagen). Beta sheet: linear strands connected side-by-side; found in silk fibroin, antibodies

The overall 3D shape of a single polypeptide. Stabilized by interactions between R-groups: hydrophobic interactions, ionic bonds, hydrogen bonds, disulfide bridges (covalent). Denaturation (heat, pH) disrupts tertiary structure

The structure formed when multiple polypeptide subunits assemble together. Not all proteins have quaternary structure. Examples: hemoglobin (4 subunits), DNA polymerase (multiple subunits). Stabilized by same forces as tertiary structure