Question

1.How do D -amino acids differ from L-amino acids? What biological roles are played by peptides that contain D -amino acids?

2.Which amino acid is technically not an amino acid? Which amino acid contains no chiral carbon atoms?

3.For each of the following, name an amino acid in which the R group contains it: a hydroxyl group, a sulfur atom, a second chiral carbon atom, an amino group, an amide group, an acid group, an aromatic ring, and a branched side chain.

4.Identify the polar amino acids, the aromatic amino acids, and the sulfur-containing amino acids, given a peptide with the following amino acid sequence:

Glu-thr-val-asp-ile-ser-ala

Answer 1

1) the amino acids contain chiral carbon. There are four different groups attahced on the carbon hence the moleucle is asymmetric. The molecule (amino acid) may acheive either of the two configuration leading to rotation of plane of polarized light in clockwise or anticlockwise direction.By convention, these are called L- and D- forms

The L-amino acids are proteogenic amino acids. the use of D-peptides in biological system is in immunity and some neurosensors.

2) Technically, Proline is not an amino acid. Infact we can call it as "imino acid"

Glycine contains no chiral carbon:

3) The examples are

4) The peptide is

Glu-thr-val-asp-ile-ser-ala

Glu: Polar [With carboxylic acid group]

Thr: polar [With Hydroxyl group]

Asp: polar [With carboxylic acid group]

Ser: Polar [With Hydroxyl group]

No amino acid with aromatic ring or sulphur