Question

In studying a particular biomolecule (a protein, nucleic acid, carbohydrate, or lipid) in the laboratory, the biochemist first needs to separate it from other biomolecules in the sample (that is, it needs to be purified). Specific purification techniques are described later in the text. However, by looking at the monomeric subunits and functional groups of a biomolecule, you should have some ideas about the characteristics of the molecule that would allow you to separate it from other molecules. Look for differences in ionizable groups, polarity, solubility in water, size, and shape. Based on the characteristics of each type of molecule, select the way(s) in which amino sugars such as glucosamine could be separated from steroid hormones such as estradiol.

the solubilities of the two molecules in water the presence of a positively charged group on one molecule the presence of a negatively charged group on one molecule OH H-C-NH3 HO-C-H Scroll down to complete this question. H-C-OH H-C-OH CH2OH HO

Answer 1

Separation of amino sugar like glucosamine from steroid hormone like estradiol:

​solubilities of the two molecules in water

Although steroidal hormones like estradiol may contain one or two hydroxyl groups, the presence of three or more cycloalkyl groups (which are hydrophobic in nature) significantly decreases their solubility in water. Solubility of steroidal hormones in water is very low. (solubility of estradiol in water is 3.6 mg per litre). Amino sugars have many hydroxy groups and a amino group. Hence, amino sugars are very polar and soluble in water.

A mixture of glucosamine and estradiol can be separated by treating the mixture with water. All glucosamine dissolve in water. Presence of any estradiol in the aqueous solution can be removed by extraction using non-polar or less polar organic solvents like ethyl acetate or diethyl ether.

Solubility of amino sugars in water is very much enhanced when they are in form of ammonium salts, that is, when they have -N⁺H₃ group ( as shown in figure in question for glucosamine). Therefore, separation of ammonium salt of the amino sugar steroidal hormones is much more facile.

presence of positively charged group on one molecule:

​Presence of positively charged group on one molecule (amino sugars) can be used to separate the compounds by ionexchange chromatography method. The positively charged amino sugar binds to cation exchange resin whereas the steroid does not. The amino sugar can be released from the resin by washing it with dilute hydrochloric acid solution.

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Separation of nucleotides like uridine triphosphate from sugars like glucose

Solubility in water may not help since both nucleotides and sugars are polar.

presence of negatively charged group on one molecule

The nucleotides contain phosphate groups that are negatively charged. Sugars like glucose are neutral molecule and do not carry any charge. Hence, a mixture containing both nucleotide like urdine triphosphate and sugar like glucose can be separated by ion exchange chromatography using anion exchange resin. When solution of the mixture is treated with the resin, the negatively charged nucleotide binds to the anion exchange resin whereas the sugars do not bind to the resin. The nucleotides can be released from the resin using suitable acid or salt solution.