Depending on the number and character of their functional groups, steroid molecules may show diverse reactivities. Moreover, the reactivity of a functional group varies according to its location within the molecule (for example, esters are formed readily by 3-OH groups but only with difficulty by the 11β-OH group). An important property of steroids is polarity —., their solubility in oxygen-containing solvents (., water and alcohols ) rather than hydrocarbon solvents (., hexane and benzene ). Hydroxyl, ketonic, or ionizable (capable of dissociating to form electrically charged particles) groups in a steroid molecule increase its polarity to an extent that is strongly influenced by the spatial arrangement of the atoms within the molecule.
The early steps in the biosynthesis of steroids of both plants and animals are the same, except that in plants lanosterol is replaced by the related compound cycloartenol, which contains a three-membered ring (C9, C10, C19) in lieu of the nuclear double bond of lanosterol. The side chains of the phytosterols, such as stigmasterol, and of the sterol ergosterol of yeasts and other fungi contain extra carbon atoms that are incorporated in reactions involving S -adenosylmethionine, which donates methyl groups in numerous biological processes. Although most plant tissues contain only traces of cholesterol, this sterol is the biogenetic precursor of such important plant steroids as the sapogenins , glycosides , and alkaloids . Because pregnane derivatives are intermediates in some of these transformations, plants and animals appear to have important features of steroid metabolism in common.
Steroid isolation , depending on context, is the isolation of chemical matter required for chemical structure elucidation, derivitzation or degradation chemistry, biological testing, and other research needs (generally milligrams to grams, but often more  or the isolation of "analytical quantities" of the substance of interest (where the focus is on identifying and quantifying the substance (for example, in biological tissue or fluid). The amount isolated depends on the analytical method, but is generally less than one microgram.  [ page needed ] The methods of isolation to achieve the two scales of product are distinct, but include extraction , precipitation, adsorption , chromatography , and crystallization . In both cases, the isolated substance is purified to chemical homogeneity; combined separation and analytical methods, such as LC-MS , are chosen to be "orthogonal"—achieving their separations based on distinct modes of interaction between substance and isolating matrix—to detect a single species in the pure sample. Structure determination refers to the methods to determine the chemical structure of an isolated pure steroid, using an evolving array of chemical and physical methods which have included NMR and small-molecule crystallography .  : 10–19 Methods of analysis overlap both of the above areas, emphasizing analytical methods to determining if a steroid is present in a mixture and determining its quantity.