Chapter 4 section 4

Question 1

Which amino acid is not chiral?

Answer 1

Glycine.

Question 2

What makes an amino acid chiral?

Answer 2

Four different groups attached to the α-carbon.

Question 3

What are enantiomers?

Answer 3

Nonsuperimposable mirror-image isomers of a chiral molecule.

Question 4

What is optical activity?

Answer 4

The ability of a molecule to rotate plane-polarized light.

Question 5

What do (+) and (−) indicate in amino acids?

Answer 5

(+) is dextrorotatory (clockwise rotation), (−) is levorotatory (counterclockwise).

Question 6

What configuration do protein amino acids usually have?

Answer 6

L-configuration.

Question 7

What are the two common systems to describe chiral molecules?

Answer 7

D,L system and (R,S) system.

Question 8

To what molecule are all D,L amino acid configurations referenced?

Answer 8

Glyceraldehyde.

Question 9

What configuration do most natural protein amino acids have?

Answer 9

L-configuration.

Question 10

Where are D-amino acids found in nature?

Answer 10

Certain peptide antibiotics (e.g., valinomycin, gramicidin, actinomycin D) and some microbial cell walls.

Question 11

Why is the (R,S) system preferred over D,L for some molecules?

Answer 11

It unambiguously describes molecules with two or more chiral centers.

Question 12

Give an example of an amino acid with two chiral centers.

Answer 12

Threonine (L-threonine = (2S,3R)-threonine).

Question 13

What is special about GFP (green fluorescent protein) from Aequorea victoria?

Answer 13

Its light emission is autocatalytic, requiring only the protein itself (serine, tyrosine, glycine form the chromophore).

Question 14

How is GFP used in genetic engineering

Answer 14

GFP can be fused to any gene to visualize its expression in cells.

Question 15

What is the “brainbow” technique?

Answer 15

Random expression of multiple fluorescent proteins in neurons to label many cells in different colors for circuit mapping.