Protein Structure FDSC400

Protein Functions Biological?Food?

Protein Structure 20 Amino Acids Primary Secondary Tertiary Quaternary Denatured ( ) Coded in DNA Self assembly to a single (native) structure. Depends on primary structure and solution conditions Common in foods. Many non- native forms depending on protein structure, solution conditions (& history) and ingredient interactions

Amino Acids The monomer unit of proteins R is the side chain. One of 20 different chemical compounds Some R-groups are acid (other alkali) Some R-groups are water soluble (others are not) Chiral carbon (L-series)

Amino Acids Polar Uncharged. Ser, Thr, Asn, Gln, Cys Positive (basic). Arg, Lys, His Negative (acidic). Asp, Glu, Non-Polar Aliphatic. Ala, Ile, Leu, Met, Pro, Val Aromatic. Phe, Trp, Tyr

Example Amino Acids Alanine Glutamic acid Phenylalanine

Peptide Bonds Water Amino acids

Peptide Bonds OCNHOCNH OCNHOCNH : - +

Disulfide Bonds Two cysteine molecules under oxidizing conditions Intermolecular or intramolecular cross- link

 -Helix N-H to C=O hydrogen bonds in 4 th succeeding A.A. Hydrogen bonds parallel to axis Typically amphiphilic

Amphiphilic 2° Structures Hydrophilic Hydrophobic

 -Sheet C=O and N-H perpendicular to chain form inter-segment H-bonds Parallel or antiparallel  -strands typically 5-15 A.A. More stable than  -helix  -sheet

Hydrophobic amino acids Peptide chain Protein Folding

Tertiary Structure

Types of Tertiary Structure GlobularDisorderedFibrous Many insoluble amino acids, protein tends to minimize surface/volume ratio Interacts well with water and takes up a random configuration Strong secondary structure allows protein to retain a non-spherical shape

Quaternary Structure Folded protein unable to contain some hydrophobic residues Dimerized protein shields the hydrophobic amino acids from water