Protein Structure
FDSC400
Protein Functions
• Biological? • Food?
Protein Structure
20 Amino Acids
Coded in DNA
Primary
Secondary Self assembly to a single (native)
structure. Depends on primary
structure and solution conditions
Tertiary
( Quaternary ) Common in foods. Many non-
native forms depending on protein
structure, solution conditions (&
Denatured history) and ingredient
interactions
Amino Acids
• The monomer unit of proteins
•R is the side chain.
R
•One of 20 different
O
C C NH 2
chemical compounds
H •Some R-groups are acid
HO
(other alkali)
Chiral carbon
•Some R-groups are water
(L-series) soluble (others are not)
Amino Acids
Polar Non-Polar
• Uncharged. Ser, Thr, • Aliphatic. Ala, Ile,
Asn, Gln, Cys Leu, Met, Pro, Val
• Positive (basic).
Arg, Lys, His • Aromatic. Phe, Trp,
Tyr
• Negative (acidic).
Asp, Glu,
Example Amino Acids
Alanine
Phenylalanine
Glutamic acid
Peptide Bonds
R
O
C C NH 2
R H
O HO
C C
H
NH 2
R Amino acids
HO O
R C C NH 2
O H
C C NH
H
HO
Water
Peptide Bonds
O
O H
N
:
C N N
H
O R
H
O- H O
+ +
C N
N +
N
H
H
O R
Disulfide Bonds
• Two cysteine
C SH HS C molecules under
H2 H2 oxidizing conditions
• Intermolecular or
[O] intramolecular cross-
link
C S S C
H2 H2
a-Helix
• N-H to C=O hydrogen
bonds in 4th
succeeding A.A.
• Hydrogen bonds
parallel to axis
• Typically amphiphilic
Amphiphilic 2° Structures
Hydrophilic
Hydrophobic
b-Sheet
• C=O and N-H perpendicular
to chain form inter-segment
H-bonds
• Parallel or antiparallel
b-strands typically 5-15 A.A.
• More stable than a-helix
b-sheet
Protein Folding
Hydrophobic
amino acids
Peptide chain
Tertiary Structure
Types of Tertiary Structure
Globular Disordered Fibrous
Many insoluble Interacts well with Strong secondary
amino acids, protein water and takes up a structure allows
tends to minimize random configuration protein to retain a
surface/volume ratio non-spherical shape
Quaternary Structure
Folded protein unable to Dimerized protein shields the
contain some hydrophobic hydrophobic amino acids
residues from water