Amide AAs

{*Figure 16*}

Asn is a very small amino acid as well as being very polar.

Amides are neutral and do not ionize nor do they accept protons (see graphics below; ie Fig. 18 & 19)

{*Figure 17*}

Gln is a bit larger amide than Asn because it has a longer side chain string of Carbons.

Both the amide AAs are neutral derivatives of the corresponding acid AAs (Asp & Glu - see below)

Understanding the chemical character of the amide is very important, since the peptide bond of proteins is an amide bond,

which will be discussed in the next lecture (see Lecture 5).

{*Figure 18*}

Amides have a partial double bond character and also a partial charge character

because of the resonance forms shown in the above graphic (Fig. 18).

{*Figure 19*}

Another way to look at the partial charge and double bond of an amide is shown above.

Since the free electrons of the Nitrogen atom are tied up in forming the partial double bond,

the Nitrogen can not accept a proton (H+). This Nitrogen also has a partial positive charge,

which tends to repel the proton (H+) and prevents it from binding to the nitrogen.