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Interactions between ligand and active site residues lead to catalysis.
Heidi L Schubert, Chris P. Hill
Department of Biochemistry, University of Utah
[email protected]
Proteins are macromolecules (heteropolymers) made up from 20 different Lamino acids, also
referred to as residues. Below about 40 residues the term peptide is frequently used. A certain
number of residues is necessary to perform a particular biochemical function, and around 40-50
residues appears to be the lower limit for a functional domain size. Protein sizes range from this
lower limit to several hundred residues in multi-functional proteins. Very large aggregates can be
formed from protein subunits, for example many thousand actin molecules assemble into a an
actin filament. Large protein complexes with RNA are found in the ribosome particles, which are
in fact 'ribozymes'.1
Amino acids
The basic structure of an amino acid is quite simple. R denotes any one of the 20 possible side
chains (see table below). We notice that the C-atom has 4 different ligands (the H is omitted in
the drawing) and is thus chiral. An easy trick to remember the correct L-form is the CORN-rule:
when the C-atom is viewed with the H in front, the residues read "CO-R-N" in a clockwise
direction.
1) http://www.ruppweb.org/Xray/101index.html Blatant plagiarism