The weight of proteins or nucleic acids in solution is commonly determined by UV spectros-copy using the Beer-Lambert law. For example, the e of double-stranded DNA at 260 nmis 6670 M21cm21. The formula weight of the repeating unit in DNA (650 Daltons onaverage) can be used as the molecular weight. What is the weight of DNA in 2.0 mL ofaqueous buffer if the absorbance, measured in a 1-cm cuvette, is 0.75?
BN Chapter 2: Atoms, Molecules, and Ions 2.1: The Early History of Chemistry Greeks first to try to explain chemical changes (400BC) o All matter composed of 4 elements: Fire, earth, water, and air o Matter Matter is continuous (infinitely divisible into smaller pieces) OR Composed of small indivisible particles o Democritus Atomos=atoms Supported small indivisible particles o No definite answer b/c no experiments Alchemy (next 2000 yrs) o Mystics obsessed w/ idea of turning cheap metal into gold o Discovery: How to prepare mineral acids Elements: mercury, sulfur, and antimony Robert Boyle, the first "chemist" (1600's) o Measured the relationship b/t pressure & the volume of gases o Element=substance that cannot be broken down further Combustion (17th-18th cent.) o Georg Stahl: phlogiston flowed out of burning material--stopped burning b/c container filled w/ phlogiston Phlogiston: substance believed in the 18th cent. that exist in all combustible bodies; released in combustion o Joseph Priestley: vigorous combustion, low in phlogiston o Priestley's observations did not contradict Stahl's--diff. theories for WHY 2.2: Fundamental Chemical Law