Question

Which one of the following structures represents the peptide chain?

• A. $-\stackrel{\underset{|}{H}}{N}-\underset{\stackrel{||}{O}}{C}-\underset{\stackrel{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-NH-\stackrel{\underset{||}{O}}{C}-NH-$
• B. $-\stackrel{\underset{|}{H}}{N}-\underset{\stackrel{||}{O}}{C}-\underset{|}{\stackrel{|}{C}}--\underset{|}{\stackrel{|}{C}}-\underset{|}{\stackrel{|}{C}}-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\underset{|}{\stackrel{|}{C}}-\underset{|}{\stackrel{|}{C}}$
• C. $-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\underset{\stackrel{||}{O}}{C}-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\underset{\stackrel{||}{O}}{C}-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\underset{\stackrel{||}{O}}{C}-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-$
• D. $-\underset{|}{\stackrel{|}{C}}-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\underset{|}{\stackrel{|}{C}}-\stackrel{\underset{||}{O}}{C}-\underset{\stackrel{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\underset{|}{\stackrel{|}{C}}-\stackrel{\underset{|}{H}}{N}-\underset{\stackrel{||}{O}}{C}-\underset{|}{\stackrel{|}{C}}-\underset{|}{\stackrel{|}{C}}-$

Answer 1

Answer: (C)

The peptide linkage $(-NH-CO-)$ is formed by the condensation of amino acids molecules.
$HNH-\underset{\stackrel{|}{R}}{C}H-\underset{\stackrel{||}{O}}{C}-OH$
$+H\cdot NH-\underset{\stackrel{|}{R}}{C}H-\underset{\stackrel{||}{O}}{C}-OH\to$
$-HN-\underset{\stackrel{|}{R}}{C}H-\underset{\stackrel{||}{O}}{C}-NH--\underset{\stackrel{|}{R}}{C}H-\underset{\stackrel{||}{O}}{C}$
Hence, following structure represent the peptide chain.
$-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\underset{\stackrel{||}{O}}{C}-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\underset{\stackrel{||}{O}}{C}-\stackrel{\underset{|}{H}}{N}-\underset{|}{\stackrel{|}{C}}-\stackrel{\underset{||}{O}}{C}-$