Proteins I

Proteins I

1. intro biological macro-molecules (all polymers)

   • polysaccharides: store molecules (can be branched or unbranched)
   • proteins: function (unbranched)
   • nucleic acids: storage information (unbranched)

2. Amino acids (monomers)

   • 20 types different
     • structure draw
   • properties
     • Amphoterism
     • stereoisomerism
   • classification
     • non-polar side chains (insoluble in water)
       • hydrophobic
     • polar but uncharged side chains (soluble in water)
     • charged side chains (soluble in water)
       • hydrophilic

3. peptide bond

   • draw
     • btw carboxyl group of one amino acid and the amino group of another, liberating water molecule
   • peptide: small # of ac
     • polypeptides: large #
   • dimensions: 50-300# max lenght of 1800A and typical diameter of 5nm

4. structure

   • primary structure
     • primary sequence of ac
   • secondary structure
     • a-helix (darw)
       • ac coiled into a right handed helx with 3.6 residues/turn and 0.15 nm btw neighbouting (C atom)
       • Side chains project out of the helix
       • atoms of the polypeptide backbone pack closely within the center of the helix
       • Each backbone carbonyl oxygen (CO) hydrogen bonds to the backbone NH of the 4th residue
     • B-sheet (draw)
       • polypeptide chain is almost fully extended
       • several segments of a chain lie side by side with hydrogen bonding btw carbonyl oxygens and NHs of adjacent strands
       • adjacent chains can be parallel or antiparallel
       • side chains stick out from the faces of the sheet
     • structural motifs (combinatio of secondary structures)
       • cupersecondary structure
   • tertiary structure
     • can only be determinated by X-ray crystallography
     • fibrous proteins
       • not fold much, extended rods
         • not solubles and structural functons
           • "forces"
             • Disulphide bridges btw cysteines (strong covalent bonds)
             • lower: van der Waals forces or ionic interactions
     • globular proteins
       • dynamic functions and solubles in water
     • large proteins can be considered to be composed of 2 or more spherical regions or domains /domain may also be a unit of function in proteins with more than one functional site
   • quaternary structure: form by 2 or more sub-units of different polypeptides (Hemoglobin)
   • balance by hydrogen bonds***