Alanine exists as a zwitterion (I) in aqueous solution. In presence of acid (pH = 2), the basic - COO- group accepts a proton to give cation (II) but in presence of a base (pH = 10), the acidic - \({ NH }_{ 3 }\) group donates a proton to the base and thus exists as an anion (III).
\(\quad \quad \quad { CH }_{ 3 }\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad { CH }_{ 3 }\\ \quad \quad \quad \quad |\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad |\\ \overset { + }{ { NH }_{ 3 } } -CH-{ COO }^{ - }\quad \overset { { H }^{ + } }{ \longrightarrow } \overset { + }{ { NH }_{ 3 } } -CH-{ COO }H\\ \quad \quad Alanine\quad (I)\quad \quad \quad \quad \quad \quad \quad \quad II\)
\(\\ \quad \quad \quad { CH }_{ 3 }\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad { CH }_{ 3 }\\ \quad \quad \quad \quad |\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad |\\ \overset { + }{ { NH }_{ 3 } } -CH-{ COO }^{ - }\quad \overset { { OH }^{ - } }{ \longrightarrow } \overset { + }{ { NH }_{ 3 } } -CH-{ { COO }^{ - } }\\ \quad \quad Alanine\quad (I)\quad \quad \quad \quad \quad \quad \quad \quad III\\ \)

The Ka and Kb values of a-amino acids are very low because, in a-amino acids, the acidic group is \({ NH }_{ 3 }\) instead of -COOH in carboxylic acids and basic group is -\({ COO }^{ - }\) instead of -\({ NH }_{ 2 }\) group in aliphatic amines. For example, the Ka and Kb values of glycine are \(1.6\times { 10 }^{ -10 }\) and \(2.5\times { 10 }^{ -12 }\) respectively.

The stability of \(\alpha \) -helix structure is due to intramolecular H-bonding between -NH- and -CO- groups of the same polypeptide chain. The \(\alpha \) -helix is termed as \({ 3.6 }_{ 13 }\) helix since each turn of the helix has approximately 3·6 amino acids and the hydrogen bonding leads to the formation of a 13-membered ring.

During osazone formation, the reaction occurs only at CI and C2 while rest of the molecule remains intact. Since glucose and fructose differ from each other only in the arrangement of atoms at CI and C2, therefore, they. give the same osazone.

Carbohydrates which differ in configuration at the glycosidic carbon (i.e. \({ C }_{ 1 }\) in aldoses and \({ C }_{ 2 }\) in ketoses) are called anomers while those which differ in configuration at any carbon other than glycosidic carbon are called epimers. For example, \(\alpha \)-D-glucose and \(\beta \)-D-glucose are anomers since they differ in configuration at \({ C }_{ 1 }\) (glycosidic carbon) while glucose and mannose are called epimers since they differ in configuration at \({ C }_{ 2 }\)(other than the glycosidic carbon \({ C }_{ 1 }\) ). In other words, glucose and mannose are Cr epimers. Similarly, we can show that glucose and galactose are \({ C }_{ 4 }\) -epimers since they differ in configuration only at \({ C }_{ 4 }\).