AP Biology Unit 1 Study Guide: Chemistry of Life

Vocabulary practice flashcards covering chemical bonds, elements of life, functional groups, properties of water, biomolecules, and protein folding from the AP Biology Unit 1 Study Guide.

Electronegativity

An atom's capacity to pull shared electrons toward itself in a chemical bond, determined by atomic number, valence electron distance from the nucleus, and electron tendency.

Covalent Bond

A strong, difficult-to-break chemical bond formed by the sharing of valence electrons between atoms; forms the structural backbones of organic macromolecules.

Nonpolar Covalent Bond

A bond formed by equal electron sharing due to similar electronegativities, producing no partial charges; found in hydrophobic regions and molecules such as $C-H$ and $O=O$.

Polar Covalent Bond

A bond characterized by unequal electron sharing due to higher electronegativity in one atom, generating partial charges ($\delta^+$, $\delta^-$); found in hydrophilic regions and molecules such as $O-H$ and $N-H$.

Ionic Bond

A chemical bond resulting from the transfer of electrons to create oppositely charged ions that attract; strong in dry crystals but dissociates in aqueous environments.

Hydrogen Bond

An attraction between a partially positive hydrogen ($\delta^+$) and an electronegative atom ($\delta^-$) on another molecule or region; weak individually but strong in high numbers.

Organic Molecule

A chemical compound containing carbon-to-hydrogen ($C-H$) bonds.

Inorganic Molecule

A chemical compound lacking carbon-to-hydrogen ($C-H$) bonds.

Functional Groups

Specific clusters of atoms attached to carbon skeletons that dictate a molecule's chemical behavior.

Hydroxyl Group

A polar functional group with the structure $-OH$.

Methyl Group

A nonpolar functional group with the structure $-CH_3$.

Carbonyl Group

A polar functional group featuring a carbon double-bonded to an oxygen atom ($C=O$).

Carboxyl Group

A charged, acidic functional group ($-COOH$) that ionizes to release $H^+$.

Amino Group

A charged, basic functional group ($-NH_2$) that ionizes to accept $H^+$.

Phosphate Group

A charged, acidic functional group containing phosphorus bonded to oxygen atoms that ionizes to release $H^+$.

Sulfhydryl Group

A polar functional group with the structure $-SH$.

Cohesion

The intermolecular attraction between identical water molecules via hydrogen bonding.

Surface Tension

A measure of the difficulty in stretching or breaking the surface of a liquid; highly elevated in water due to cohesive hydrogen bonding.

Adhesion

The attraction of water molecules to other polar surfaces.

Capillary Action

The upward movement of water in narrow spaces combining cohesion and adhesion, seen in plant xylem and capillary tubes.

High Specific Heat

The amount of heat that must be absorbed or lost for $1\,g$ of a substance to change temperature by $1^\circ\text{C}$; in water, heat is initially absorbed to break hydrogen bonds before molecules move faster.

High Heat of Vaporization

The amount of energy required to convert $1\,g$ of liquid into gas.

Evaporative Cooling

The process by which the surface of an object cools during evaporation as the highest-energy water molecules transition into gas (e.g., sweating, panting, transpiration).

Density of Ice

The physical property wherein solid water is ~$10\%$ less dense than liquid water because hydrogen bonds below $4^\circ\text{C}$ lock into a stable, rigid crystalline lattice holding molecules farther apart.

Hydration Shell

A sphere of water molecules surrounding dissolved ions through partial charge interactions.

Hydrophilic

Substances that are polar or charged and readily dissolve in water (e.g., salts, sugars, polar amino acids).

Hydrophobic

Nonpolar substances that do not dissolve in water because water molecules preferentially form hydrogen bonds with each other (e.g., lipids, steroids).

Monomer

A single repeating subunit used as a building block to synthesize polymers.

Polymer

A long chain of monomers linked together by covalent bonds.

Dehydration Synthesis

An energy-requiring reaction that joins monomers into polymers by removing $H_2O$ (one monomer loses $-OH$, the other loses $-H$) to form a covalent bond.

Hydrolysis

An energy-releasing reaction that breaks covalent bonds in polymers to produce monomers by adding $H_2O$, splitting it into $-OH$ and $-H$ attached to adjacent subunits.

Carbohydrate

A biomolecule composed of Carbon ($C$), Hydrogen ($H$), and Oxygen ($O$), formed from monosaccharide monomers and polysaccharide polymers, providing fast energy and structural cellulose in plant cell walls.

Lipid

A biomolecule composed of Carbon ($C$), Hydrogen ($H$), Oxygen ($O$), and sometimes phosphorus ($P$); lacks a true monomer or polymer and functions in cell membranes, long-term energy storage, thermal insulation, and hormones.

Protein

A biomolecule composed of Carbon ($C$), Hydrogen ($H$), Oxygen ($O$), Nitrogen ($N$), and sometimes sulfur ($S$), consisting of amino acid monomers joined into polypeptide chains.

Nucleic Acid

A biomolecule composed of Carbon ($C$), Hydrogen ($H$), Oxygen ($O$), Nitrogen ($N$), and Phosphorus ($P$), consisting of nucleotide monomers that assemble into DNA and RNA to store and transmit genetic information.

Phosphodiester Bond

The covalent bond that links nucleotide monomers together along a nucleic acid strand.

Primary Structure ($1^\circ$)

The specific, linear sequence of amino acids in a polypeptide chain encoded directly by DNA.

Secondary Structure ($2^\circ$)

Localized hydrogen bonding along the polypeptide backbone that forms $\alpha$-helices and $\beta$-pleated sheets.

Tertiary Structure ($3^\circ$)

The overall three-dimensional shape of a polypeptide resulting from R-group interactions, including hydrophobic clustering, hydrogen bonds, ionic bonds, and covalent disulfide bridges.

Quaternary Structure ($4^\circ$)

The structural association formed by two or more independent polypeptide subunits joining together (e.g., hemoglobin, collagen).

Denaturation

The disruption of a protein's secondary ($2^\circ$), tertiary ($3^\circ$), and quaternary ($4^\circ$) structure caused by changes in temperature, $pH$, salinity, or chemicals, leading to loss of biological function.