Unit 1 · Chemistry of Life

Hydrogen bond ● (core concept) — A weak attraction between a hydrogen atom carrying a partial positive charge and a nearby electronegative atom (such as oxygen or nitrogen) carrying a partial negative charge. Hydrogen bonds between water molecules cause cohesion, adhesion, and surface tension.

Polar covalent bond ● (core concept) — A covalent bond in which electrons are shared unequally, giving one end a partial negative charge and the other a partial positive charge. The polar O–H bonds make water molecules polar and able to form hydrogen bonds.

Cohesion ● (core concept) — Attraction between molecules of the same substance. In water, hydrogen bonding between molecules produces cohesion, such as water beading into droplets.

Adhesion ● (core concept) — Attraction between molecules of different substances. Hydrogen bonding lets water adhere to other polar surfaces, such as water climbing the walls of a narrow tube.

Surface tension ● (core concept) — The tight, elastic-like surface of water caused by hydrogen bonding pulling surface water molecules toward one another.

Specific heat capacity ● (core concept) — The amount of heat energy needed to raise the temperature of 1 gram of a substance by 1°C. Water's high specific heat capacity helps living organisms maintain stable body temperatures.

Heat of vaporization ● (core concept) — The heat energy required to convert liquid water into water vapor. Water's high heat of vaporization makes evaporative cooling an effective way to remove body heat.

Elements of life ● (core concept) — Carbon, hydrogen, and oxygen are the most prevalent elements in biological molecules. Sulfur is used to build proteins, phosphorus is used in phospholipids and nucleic acids, and nitrogen is used in nucleic acids.

Hydrolysis ● (core concept) — A chemical reaction that breaks the covalent bonds between monomers by adding a water molecule: a hydrogen ion attaches to one monomer and a hydroxyl group to the other.

Dehydration synthesis ● (core concept) — A chemical reaction that joins two monomers with a covalent bond, removing a hydrogen ion from one monomer and a hydroxyl group from the other — releasing the equivalent of a water molecule.

Polymer ● (core concept) — A large molecule built from many repeating subunits (monomers) joined by covalent bonds.

Monomer ● (core concept) — A small molecular subunit that can join with others to form a polymer.

Polymerization ● (core concept) — The process of linking many monomers together into a polymer.

Monosaccharide ● (core concept) — A simple sugar; the monomer building block of carbohydrates.

Polysaccharide ● (core concept) — A complex carbohydrate polymer made of monosaccharides joined by covalent bonds; it may be linear or branched.

Starch ○ — A storage polysaccharide in plants, built from glucose monomers. Listed as an illustrative (suggested, not required) example in the CED.

Glycogen ○ — A storage polysaccharide in animals, built from glucose monomers. Listed as an illustrative (suggested, not required) example in the CED.

Cellulose ○ — A structural polysaccharide in plant cell walls, built from glucose monomers. Listed as an illustrative (suggested, not required) example in the CED.

Lipid ● (core concept) — Typically nonpolar, hydrophobic molecules whose structure and function are derived from the way their subcomponents are assembled. Fatty acids, a key subcomponent, can be described as either saturated or unsaturated.

Saturated fatty acid ● (core concept) — A fatty acid whose carbon chain contains only single bonds between carbon atoms.

Unsaturated fatty acid ● (core concept) — A fatty acid containing at least one carbon–carbon double bond, which kinks the carbon chain. More double bonds make a lipid more unsaturated and more liquid at room temperature.

Fat ● (core concept) — A lipid that provides energy storage and supports cell function; in mammals, fats can also provide insulation that helps keep the body warm.

Steroid ● (core concept) — A type of lipid that includes cholesterol; steroid hormones support physiological functions including growth and development, energy metabolism, and homeostasis.

Cholesterol ● (core concept) — A steroid that provides essential structural stability to animal cell membranes.

Phospholipid ● (core concept) — A lipid whose molecules group together to form the lipid bilayers found in plasma and cell membranes.

Nucleotide ● (core concept) — The monomer of nucleic acids, composed of a five-carbon sugar (deoxyribose or ribose), a phosphate group, and a nitrogenous base (adenine, thymine, guanine, cytosine, or uracil).

Deoxyribose ● (core concept) — The five-carbon sugar found in DNA.

Ribose ● (core concept) — The five-carbon sugar found in RNA.

Nitrogenous base ● (core concept) — One of the five bases found in nucleotides: adenine, thymine, guanine, or cytosine in DNA, with uracil replacing thymine in RNA.

Antiparallel double helix ● (core concept) — The structure of DNA: two nucleotide strands running in opposite 5′-to-3′ directions, twisted into a double helix.

Base pairing ● (core concept) — In DNA, adenine pairs with thymine (A–T) and cytosine pairs with guanine (C–G) via hydrogen bonds; in RNA, adenine pairs with uracil (A–U).

5′ and 3′ ends ● (core concept) — The directionality of a nucleic acid strand, defined by the 5′ phosphate and 3′ hydroxyl ends of its sugars. During nucleic acid synthesis, new nucleotides are added to the 3′ end of the growing strand, resulting in the formation of covalent bonds between nucleotides.

DNA and RNA strands ● (core concept) — DNA is typically double stranded, while RNA is typically single stranded.

Amino acid ● (core concept) — The monomer of proteins: a central carbon atom bonded to a hydrogen atom, a carboxyl group, an amine group, and a variable R group.

Peptide bond ● (core concept) — The covalent bond linking amino acids in a protein, formed between the carboxyl group of one amino acid and the amine group of the next.

Polypeptide ● (core concept) — A linear chain of amino acids joined by peptide bonds.

R group ● (core concept) — The variable side chain of an amino acid. Its chemical properties — hydrophobic/nonpolar, hydrophilic/polar, or ionic — determine the structure and function of that region of the protein.

Primary structure ● (core concept) — A protein's sequence of amino acids. This sequence determines the protein's overall shape.

Secondary structure ● (core concept) — Local folding of a protein's polypeptide backbone — forming shapes such as alpha-helices and beta-pleated sheets — held by hydrogen bonds between backbone atoms.

Alpha-helix ● (core concept) — A coiled secondary structure of a protein, formed by hydrogen bonding within the polypeptide backbone.

Beta-pleated sheet ● (core concept) — A folded, sheet-like secondary structure of a protein, formed by hydrogen bonding within the polypeptide backbone.

Tertiary structure ● (core concept) — A protein's overall three-dimensional shape, stabilized by hydrogen bonds, hydrophobic interactions, ionic interactions, and disulfide bridges.

Disulfide bridge ● (core concept) — A covalent bond between sulfur atoms that helps stabilize a protein's tertiary structure.

Quaternary structure ● (core concept) — Protein structure arising from interactions between multiple polypeptide chains. All four levels of protein structure together determine a protein's function.