Chapter 4 section 5

Question 1

Which amino acids absorb significant ultraviolet (UV) light above 250 nm?

Answer 1

Phenylalanine, tyrosine, and tryptophan.

Question 2

Can amino acids absorb visible light?

Answer 2

No, none absorb in the visible region.

Question 3

Do all amino acids absorb infrared (IR) light?

Answer 3

Yes, all amino acids absorb in the IR region.

Question 4

Why is the UV absorption of aromatic amino acids useful?

Answer 4

It allows spectroscopic determination of protein concentration.

Question 5

Which aromatic amino acid can exhibit phosphorescence?

Answer 5

Tryptophan.

Question 6

What additional property do aromatic amino acids show besides UV absorption?

Answer 6

Weak fluorescence, useful in studying protein structure and dynamics

Question 7

What does NMR detect in amino acids?

Answer 7

NMR detects absorption of radio-frequency energy by nuclei

Question 8

What can high-field NMR determine about proteins?

Answer 8

Three-dimensional structures of peptides and proteins.

Question 9

What is the configuration of most natural amino acids?

Answer 9

L-configuration; most have S-configuration at the α-carbon except cysteine (R-configuration).

Question 10

How are R and S configurations assigned?

Answer 10

View from the lowest priority group; clockwise = R, counterclockwise = S.