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Unformatted text preview: Protein Structure Monday. October 30. 2006 10:30AM Proteins Structure Classiﬁcat Structural proteins, binding proteins (regulatory), catalytic proteins
ions (enzymatic), membrane proteins, contractile proteins (motility), immune
system proteins (antibodies)
Primary Proteins are composed of 20 amino acid monomers, the sequence for which is
structure encoded in the genetic code. The primary structure of a polypeptide is the
linear sequence ofamino acids.
HzN //C —OH
0 Only the L-o-amino acid We): is used in nature (CORN spelled clockwise).
Amino acids (called a residue when dehydrated in a polypeptide chain) have an amino terminal, a carboxyl terminal, and an o’carbon joining the functional
group to the terminals. Amino acids can be classiﬁed are hydrophobic, polar uncharged, or polar
charged. Residuedoubie Rotation around the single bonds ofthe main chain and the side chains
bond character allows the shape to change. However, the peptide bond has partial double bond character, preventing free rotation there. 0 /CH3 0\ (c H3
/c —N \ : /c =N:
HaC H HaC H This means that gig and trans isomers can exist. The trans isomer is
favored 100ml because of steric reasons. Peptide
bonding R R'
l l 'H20 CH
CH + CH —- x \ / \CH’
/ \ / \ H C
HZN COOH HZN COOH 2N ll NHz—) COOH bonding direction.
The main chain ofa polypeptide is the backbone and the side chains are
the function groups. rota ticm Main chain II! (phi) and q; (psi) are used to describe the angles of rotation between the nitrogen atom and the o-carbon atom, and the o-carbon atom and the carbonyl
carbon atom, respectively. Because ofs’tegig hindrances between functional groups on each residue, only
certain angles can be achieved. Secondary Hydrogen bonding interactions between on the primary structure stabilize the structure polypeptide chain into a regular structure were in and w are always the same.
Two structures that are formed are the oihelix and the Bipleated sheet. The
strands of a ﬁ-p eated sheet are helices as well. Protein motifs These are common patterns that eXISt as structures between (W secondary and tertiary. B-o-B is an example. structure) Tertiary The tertiary structure is formed by various interactions between functional structure groups. This structure is globular. V
structure Quaternar Multiple polypeptide chains can associate together to form the biological structure of an W protein. Often the chains are identical and are called mm. When the polypeptides are different, they are mm as
subunits. Quaternary structures are closed molecules: all the W must
have equal environments. stabilizing The strongest Forces are the hydrophobic interactions of nonpolar funtional
forces groups clustering together in water. Hydrogen ponds, ionic bondsmfide bonds also cause interactions. Sulfide bonds are the only covalent bonds
involved here. Biological The final structure ofa protein that is fundamental to the biological function structure ofthe molecule. Every protein has a unique chemical topography endowing
the molecule with a strict specificity. ...
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- Fall '07