文档介绍：Previously published in
Biophysical Society On-line Textbook
PROTEINS
CHAPTER 1. PROTEIN STRUCTURE
Section 1.
Primary structure, secondary motifs,
tertiary architecture, and anization
te Carey* and Vanessa Hanley^
*Department of Chemistry
^Department of Chemical Engineering
Princeton University
Princeton, NJ 08544-1009
*corresponding author
(609) 258-1631 phone
(609) 258-6746 FAX
******@
1. The amino acid building blocks
Proteins are polymeric chains that are built from monomers called amino
acids. All structural and functional properties of proteins derive from the chemical
properties of the polypeptide chain. There are four levels of protein structural
organization: primary (1°), secondary (2°), tertiary (3°), and quaternary (4°). Primary
structure is defined as the linear sequence of amino acids in a polypeptide chain.
The secondary structure refers to certain regular geometric figures of the chain.
Tertiary structure results from long-range contacts within the chain. The quaternary
structure is anization of protein subunits, or two or more independent
polypeptide chains.
Amino acids are the chemical constituents of proteins, and are characterized
by a central alpha carbon atom. The alpha indicates the priority position from which
the numbering follows for all subordinate groups. Four substituents are connected
to this Ca : one substituent is the alpha proton -H, another is the side chain -R that
gives rise to the chemical variety of the amino acids, the third is the carboxylic acid
functional group (-COOH), and the fourth is the amino functional group (-NH). The
a carbon is the asymmetric center of the molecule for all 20 amino acids except
glycine, which has only a proton as its side chain. The configuration about the a
carbon center must be the L-isomer for proteins synthesized on the ribosome. This is
probably an accident of chemical evolution where the L-isomer happens to be the
one chos