Appendix 5 - Units in the Biochemistry Laboratory

Summary

In the biochemistry laboratory course there is a strong emphasis on the manner in which data is reported to the instructor. As you may remember from your freshman chemistry laboratory experience, keeping a close watch on the units of your results will help you when calculations must be performed via dimensional analysis. The system of units most readily recognized and used by biochemists the world over is the International System of Units (SI). The SI system is rooted in 7 fundamental base units of measure (see Table A5.1). A description of the units, which are most regularly used in the biochemistry lab will follow. Biochemistry experiments and instrumentations mostly involve a range of different units. Students are required to know the multiple units and their prefix to report the quantities in conventional terms (Table A5.2).

Of the seven basic units listed in Table A5.1, the unit used most often in the biochemistry laboratory is the mole. The mole and its multiple unit forms mmol, μmol and nmol are put to use in biochemistry whenever the amount of some chemical is to be determined/reported. Closely associated with the use of the mole quantity, is mass and its accompanying units. Prior to the description of mass and the most used multiple unit forms of mass it is important for the biochemistry student to be reminded of the difference between mass and weight. In general, the mass of an object is a uniform measure of the quantity (amount) of matter in an object. Weight, on the other hand, is the attraction affinity between an object and its environment (object's placement on earth). Recall that weight (W) can be expressed in the following formula:

Inclusion of the gravity term in the above equation indicates that objects at higher altitudes will weigh less than the same object at low altitudes, while the mass of the object remains the same. In the biochemistry lab, the mass multiple unit form that a student will most likely encounter will be increasingly small amounts from grams (g) to nanograms (ng). You will most often encounter g when weighing solids for making mixtures. The smaller quantities of mg, μg and ng will be encountered when the mass of an isolated product is tabulated.