Question

1. Choose the incorrect statement
out of the followings
Answer
A.
Aspartic acid is acidic amino acid
B.Glycine is optically inactive
C.Tyrosine is a modified type of
amino acid
D. Phenylalanine is aromatic amino
acid​

Answer 1

Answer:

One of the most useful manners by which to classify the standard (or common) amino acids is based on the polarity (that is, the distribution of electric charge) of the R group (e.g., side chain).

Group I: Nonpolar amino acids

Group I amino acids are glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, and tryptophan. The R groups of these amino acids have either aliphatic or aromatic groups. This makes them hydrophobic (“water fearing”). In aqueous solutions, globular proteins will fold into a three-dimensional shape to bury these hydrophobic side chains in the protein interior. The chemical structures of Group I amino acids are:

Isoleucine is an isomer of leucine, and it contains two chiral carbon atoms. Proline is unique among the standard amino acids in that it does not have both free α-amino and free α-carboxyl groups. Instead, its side chain forms a cyclic structure as the nitrogen atom of proline is linked to two carbon atoms. (Strictly speaking, this means that proline is not an amino acid but rather an α-imino acid.) Phenylalanine, as the name implies, consists of a phenyl group attached to alanine. Methionine is one of the two amino acids that possess a sulfur atom. Methionine plays a central role in protein biosynthesis (translation) as it is almost always the initiating amino acid. Methionine also provides methyl groups for metabolism. Tryptophan contains an indole ring attached to the alanyl side chain.

Group II: Polar, uncharged amino acids

Group II amino acids are serine, cysteine, threonine, tyrosine, asparagine, and glutamine. The side chains in this group possess a spectrum of functional groups. However, most have at least one atom (nitrogen, oxygen, or sulfur) with electron pairs available for hydrogen bonding to water and other molecules. The chemical structures of Group II amino acids are:Two amino acids, serine and threonine, contain aliphatic hydroxyl groups (that is, an oxygen atom bonded to a hydrogen atom, represented as ―OH). Tyrosine possesses a hydroxyl group in the aromatic ring, making it a phenol derivative. The hydroxyl groups in these three amino acids are subject to an important type of posttranslational modification: phosphorylation (see below Nonstandard amino acids). Like methionine, cysteine contains a sulfur atom. Unlike methionine’s sulfur atom, however, cysteine’s sulfur is very chemically reactive (see below Cysteine oxidation). Asparagine, first isolated from asparagus, and glutamine both contain amide R groups. The carbonyl group can function as a hydrogen bond acceptor, and the amino group (NH2) can function as a hydrogen bond donor.