CHE 211 Study Guide - Final Guide: Carboxylate, Stereocenter, Isoelectric Point
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Organic Chemistry 2: Proteins
Protein Building Blocks: the α-Amino Acids
▪ Proteins are long polymer chains formed from the
combination of 20 different amino acid subunit called:
monomers
▪ The general structure for all amino acids, with the
exception of proline, is shown on the right
▪ An amino acid is a class of organic compounds that
contains both a primary amino group (NH2) and a carboxyl group (COOH) and an
alkyl group represented by the symbol (R)
▪ Proline is the only exception to this, it contains a secondary amino group (NH),
that is bonded to the alkyl side chain forming a cyclic amino acid
▪ The amino acids found in proteins are always the alpha amino acids, which means
the amino group and carboxyl group are bonded to the SAME carbon atom the
carbon atom that bears both the amino group and carboxyl group is called the α-carbon
atom
▪ Attah α-carbon to a:
• Carboxylate group
• Protonated amino group
▪ You will see that the carboxyl group is deprotonated in the image to
the right (α-carboxylate group) and the aio group has ee protoated (α-amino
group)
▪ At physiologic pH (pH = 7), this is what is required in most life forms, the amino acid has:
o Carboxyl group in COO- (we will NOT find a protonated carboxyl group at pH 7)
o The amino group in -NH3+ (we will NOT find a deprotonated amino group at pH
7)
o Neutral molecule with equal number of + and – charges is a zwitterion
therefore, all amino acids in water will exist as the zwitterion
o Amino acids are white crystalline solids with high melting points and high-water
solubilities; by changing the pH, you can affect the net charge on the zwitterion
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