3-4 PEPTIDE BONDS

The linear sequence of amino acids in a polypeptide chain is called the
_______________ structure of a protein. The secondary, tertiary, and quaternary
structures will be studied in future chapters.

The linkage formed between amino acids is an _______________ bond called a
_______________ bond.

The linkage is the result of a _______________ reaction between the _______________
group of one amino acid and the _______________ group of another amino acid,
resulting in the loss of a _______________ molecule. The resulting polypeptide has no
ionic _______________.

These reactions are not thermodynamically favored because of the abundance of water in
a cell, but the pathway of protein synthesis (_______________) includes reaction
intermediates that _______________ this limitation.

Linked amino acids in a polypeptide chain are referred to as amino acid
_______________. The names change, replacing –ine or –ate with _____.

Write an equation for the formation of a peptide bond between alanine and serine.

The product is named _______________ because alanine is converted to an acyl unit, but
serine retains its carboxyl group.

The free amino group at the end of a peptide chain is called the ___ – terminus, and the
free carboxyl group on the other end of a peptide chain is called the ___ – terminus.

Amino acids in a peptide chain are numbered from the N–terminus to the C–terminus
because this corresponds to the direction of protein _______________.

Both the standard 3-letter abbreviations and the one-letter abbreviations are used to
describe the sequence of amino acid residues. It’s important to know both abbreviation
systems.

Because the ionic charges of the carboxyl group and the amino groups are lost during the
formation of peptide bonds, most of the ionic charges are contributed by the
_______________ chains of the amino acids.
o This affects the _______________, _______________ properties, and because the
side chains interact with each other, the _______________and_______________
of a protein.

Some peptides are important biological compounds. For example…
o Hormones like _______________ (regulate pain in vertebrates)
o Food additives like _______________ (200 times sweeter than table sugar)
o _______________ from snake venom and poisonous mushrooms
Ex:

Aspartame is the methyl ester of aspartylphenylalanine. Show an equation that represents
the formation of this dipeptide.