Exam II

Question 1

What is the UV absorbance of a protein?

Answer 1

280nm: π-π* transition of aromatic AAs (incl. Trp, Tyr)
210nm: peptide bond

Question 2

What is the UV absorbance of a nucleic acid?

Answer 2

~260nm: π-π* transition of bases

Question 3

What method is used to assess purity of nucleic acid samples?

Answer 3

A260/A280 ratio

Ratios significantly lower than ~1.8 (DNA) or ~2.0 (RNA) may indicate protein contamination

Question 4

What method is used to assess purity of nucleic acid samples?

Answer 4

A260/A280 ratio

Ratios significantly lower than ~1.8 (DNA) or ~2.0 (RNA) may indicate protein contamination

Question 5

What can be said about a molecule that differentially absorbs left or right circularly polarised light?

Answer 5

The molecule is optically active or chiral

Question 6

Enantiomers are identical except for what two exceptions?

Answer 6

They way they interact with circularly polarised light and with other chiral molecules

Question 7

What does FRET require?

Answer 7

a) Spectral overlap (between emission spectra of donor and excitation spectra of acceptor)
b) Distance <10nm (generally between 2-10nm)
c) Correct orientation

Question 8

Why is FRET a sensitive method for distance measurements?

Answer 8

It’s sensitivity is proportional to the inverse sixth power of the separation between the donor and the acceptor