1a.) The ultraviolet spectra of proteins are largely determined
by what three amino acids?

b.). In working with nucleic acids it is often useful to measure
the optical densities at 260 nm and 280 nm. Nucleic acids (DNA and
RNA) absorb more strongly at 260 nm than 280 nm such that the ratio
A260 : A280 ranges from 1.6 to 2.0. What might happen to the
A260:A280 ratio of a solution of nucleic acid contaminated with
protein?

c.) Proteins typically have an A260:A280 ratio less than one.
Estimate the A260:A280 ratio of a protein whose amino acid
composition includes two moles of Trp and one mole of Tyr per mole
of protein. For appropriate extinction coefficients (molar
absorptivity) use information given at
http://omlc.ogi.edu/spectra/PhotochemCAD/html/index.html Activate
the link to the appropriate amino acids and then under the
absorption spectrum activate the link to “Extinction Data”.

d.) Certain proteins lack both Trp and Tyr yet still absorb
ultraviolet light in the range of 240 nm to 270 nm. What amino acid
is responsible for this? How would the A260:A280 ratio of a protein
rich in this amino acid differ from a typical protein containing
Trp and Tyr? Use the information at the URL given above to answer
this.