Final answer:
Nucleic acids absorb UV light around 260 nm due to nitrogenous bases, while proteins absorb UV light due to aromatic amino acids like tryptophan. NADH shows an additional absorbance at 340 nm. The UV spectra of proteins can change with their conformation, differing from nucleic acids.
Step-by-step explanation:
The absorption spectra of nucleic acids differ from those of proteins primarily due to the different chromophores present in these molecules. Nucleic acids absorb ultraviolet light mainly around the 260 nm wavelength because of their nitrogenous bases, which contain conjugated pi-bonding systems resembling that in compounds like nicotinamide adenine dinucleotide (NAD*). On the other hand, proteins absorb UV light primarily due to the presence of aromatic amino acids such as tryptophan, phenylalanine, and tyrosine. For example, NADH not only absorbs at 260 nm, like NAD+, but it also exhibits a second absorbance band at 340 nm.
Moreover, while UV spectroscopy can be used to study the structure and conformation of proteins, changes in the protein structure can alter the UV spectrum as the environment around the aromatic amino acids changes. This is not typically observed with nucleic acids. The absorption spectra of nucleic acids are consistent and primarily used to measure their concentration. Nucleic acids also do not show the same kind of conformational changes that can alter their UV spectra as proteins do.