Discus Optical Properties of Biomolecules

Discus Optical Properties of Biomolecules
2.1 In a sample cell of path length l=1 cm a compound of unknown concentration is measured. For light of λ=550 nm the intensity after the sample is
reduced to 80% of the original light intensity before the sample cell, I0.
Assume that this reduction in light intensity is due solely to absorption by
the compound of unknown concentration. What is the optical density
measured in this experiment for a wavelength of 550 nm? What is the concentration of the compound when it has an extinction coefficient of ε=20
000 M1 cm1 at 550 nm?
2.2 The compound of question 2.1 also exhibits considerable fluorescence. A
second sample of this compound exhibits about half as much fluorescence
intensity as the sample of question 1. What is the approximate concentration of this sample? What possible artefacts do we have to consider in the
determination of concentrations from fluorescence intensities and how do
they affect the estimated concentration?
Discus Optical Properties of Biomolecules
2.3 Explain why tryptophan has a larger extinction coefficient, fluorescence
quantum yield and longer absorption wavelengths than the two other aromatic amino acids phenylalanine and tyrosine? What aromatic amino acid
usually dominates the fluorescence properties of proteins?
2.4 An unknown sample contains either proteins, DNA or RNA. The ratio of the
optical densities measured at 260 and 280 nm, Q = OD(260 nm)/OD(280 nm),
is 1.8 and the optical density at 280 nm is 0.1 in a standard cell of 1 cm path
length. What does the sample contain and what is its concentration?
2.5 One reaction of the human body in the cold is to reduce the blood circulation in the body’s extremities. Explain why Caucasian (white) people often
have bluish lips when they are cold.
2.6 Explain qualitatively what cooperativity means and why the principle of
cooperativity is very important for the regulation of many metabolic processes in biology.
2.7 Why are plant leaves green in the summer and orange in the autumn?
2.8 In eq. 2.5 the important Beer-Lambert law is introduced. Derive it by integration of eq. 2.2.