The absorption of ultraviolet light by RNA in the near UV (250-300 nm) is due to
ID: 89730 • Letter: T
Question
The absorption of ultraviolet light by RNA in the near UV (250-300 nm)
is due to electronic transitions within the bases. Absorption at 260 (260=10M^-1cm^1per base) is approximately twice as intense as absorption at 280 nm and decreases by about
10% when double helices form. Two RNA molecules of 22 nucleotides each, let us call
them miRNA and miRNA*, are complementary to each other and form a base paired
structure at 37C which is disrupted at 90C.
a) If the concentration of miRNA-miRNA* complex in a solution is 10 g/mL,
calculate the absorbance of the complete double helical structure at 260 nm.
Assume a path length of 1 cm and remember that each nucleotide has a molecular
weight of approximately 330.
b) What will the absorbance be at 260 nM at a temperature of 90C, when all the base
pairing has been disrupted?
c) To the miRNA solution, we added an equimolar amount of a protein called TRBP
which contains 3 tryptophan residues and 5 tyrosines, The absorption of
ultraviolet light by proteins at =280nm is largely due to tryptophan (=5000 M-1
) and tyrosine (=110M-1 cm^-1
) residues. What would the absorption of the
complex be at 280 nm?
Explanation / Answer
Answer
Based on the information given:
MW of each nucleotide = 330 g /mol
Absorption at 260nm = 10 M-cm- per base decreases by about 10% for double helix
Path length = 1cm
a)
b) What will the absorbance be at 260 nM at a temperature of 90C, when all the base pairing has been disrupted?
c) To the miRNA solution, we added an equimolar amount of a protein called TRBP which contains 3 tryptophan residues and 5 tyrosines, The absorption of ultraviolet light by proteins at 280nm is largely due to tryptophan (5000 M-1) and tyrosine (110M-1 cm^-1) residues. What would the absorption of the complex be at 280 nm?
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