Answer:
(a) Peptide linkages \[(-CO-NH-)\] are present in the primary structures of proteins while the secondary structures of proteins involve hydrogen bonding.
(b) An \[\alpha \]-amino acid has a dipolar structure. In acidic medium, it exists as a positive ion
\[\underset{\begin{smallmatrix} \\ \text{Dipolar}\,\,\text{ion} \end{smallmatrix}}{\mathop{{{H}_{3}}\overset{+}{\mathop{N}}\,-\underset{\begin{smallmatrix} | \\ R \end{smallmatrix}}{\overset{\begin{smallmatrix} H \\ | \end{smallmatrix}}{\mathop{C}}}\,-CO{{O}^{-}}}}\,+\underset{(Acid)}{\mathop{{{H}^{+}}}}\,\]\[\xrightarrow{\,}\underset{\text{(Positive}\,\,\text{ion)}}{\mathop{{{H}_{3}}\overset{+}{\mathop{N}}\,-\underset{\begin{smallmatrix} | \\ R \end{smallmatrix}}{\overset{\begin{smallmatrix} H \\ | \end{smallmatrix}}{\mathop{C}}}\,-COOH}}\,\]
In electric field, the positive ion moves towards cathode. In alkaline medium, the dipolar ion changes to anion and moves towards anode under the influence of applied electric field.
\[\underset{{}}{\mathop{{{H}_{3}}\overset{+}{\mathop{N}}\,-\underset{\begin{smallmatrix} | \\ R \end{smallmatrix}}{\overset{\begin{smallmatrix} H \\ | \end{smallmatrix}}{\mathop{C}}}\,-CO{{O}^{-}}}}\,+\underset{(Base)}{\mathop{O{{H}^{-}}}}\,\]\[\underset{\begin{smallmatrix} \\ \text{(Negative}\,\,\text{ion)} \end{smallmatrix}}{\mathop{\xrightarrow{{}}{{H}_{2}}\overset{{}}{\mathop{N}}\,-\underset{\begin{smallmatrix} | \\ R \end{smallmatrix}}{\overset{\begin{smallmatrix} H \\ | \end{smallmatrix}}{\mathop{C}}}\,-CO{{O}^{-}}}}\,+{{H}_{2}}O\]
(c) Amino acids which are not synthesized by the body are called essential acids. For example, Leucine and Lysine.
Amino acids which are synthesized by the body are known as non-essential amino acids. For example, Glycine and Alanin.
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