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
Denatured
)
Common in foods. Many nonnative forms depending on protein
structure, solution conditions (&
history) and ingredient
interactions
Amino Acids
• The monomer unit of proteins
R
O
C
C
H
NH2
HO
Chiral carbon
(L-series)
•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)
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
Phenylalanine
Glutamic acid
Peptide Bonds
R
O
C
R
C
H
NH2
HO
O
C
C
H
NH2
Amino acids
R
O
HO
R
C
O
C
C
H
NH
HO
Water
C
H
NH 2
Peptide Bonds
O
H
N
:
C
N
H
N
H
O
+
N
H
R
O
H
+
N
OC
O
O
+
R
N
H
Disulfide Bonds
C SH
H2
HS C
H2
[O]
C S S C
H2
H2
• Two cysteine
molecules under
oxidizing conditions
• Intermolecular or
intramolecular crosslink
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
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