Peptide bond—An amide bond formed between two amino acids through a condensation
(nucleophilic acyl substitution) reaction.
Phenol—An alcohol with an aromatic ring, which has slightly more acidic hydroxyl hydrogens than
other alcohols.
Phosphodiester bond—The type of bond linking the sugar moieties of adjacent nucleotides in DNA.
Physical properties—Characteristics of compounds that do not change chemical composition, such
as melting point, boiling point, solubility, odor, color, and density.
Pi (π) Bond—The bonding molecular orbital formed when two parallel p-orbitals share electrons;
exists as electrons clouds above and below the sigma (σ) bond between the two nuclei.
Polarity—An uneven distribution of charge caused by atoms in the same molecule having different
electronegativities.
Polypeptide—A molecule formed from multiple amino acids connected by peptide bonds.
Preparative thin-layer chromatography—Large-scale use of thin-layer chromatography (TLC) as a
means of purification; as the large plate develops, the larger spot of sample splits into bands of
individual compounds, which can then be scraped off and washed to yield pure compounds.
Principal quantum number (n)—Describes the shell in which an electron is found; values range
from 1 to ∞.
Protonation—The addition of a hydrogen cation (H+) to a molecule.
Pyrophosphate (PPi)—The ester dimer of phosphate ; released when a new nucleotide is
joined to a growing strand of DNA by DNA polymerase.
Quinone—A compound produced by the oxidation of a phenol containing a conjugated ring with
ketones.