213
The secondary structure comprises of localized parts of a polypeptide chain
(e.g. the α-helix or β-sheet with hydrogen bonds as their backbone. These special
structures comprise the secondary structure of protein molecules. Secondary
structure is usually due to aperiodic and periodic structures. Random coil is an
example of aperiodic structure, whereas, helical and extended are examples of
periodic structure. Stability of these structures are provided by decrease in local
free energy by the rotation of φ and ψ angles, local non-covalent interactions
between amino acid side chains, as well as hydrogen bonding between CO and
N-H groups (Nelson and Cox 2013; Voet et al. 2013).
(a). Alpha-helix proteins: The secondary structure of some proteins is essentially all alpha-helices. Myoglobin is a good example of this type. Damodaran
HO
HO
H 3 C
H 3 C
H
HS
C C
C
O
O
C
OH
H 2
NH 2
H 2 N
H 2
H 2
H
O
O
C C
C
C
C
H 2 H
NH 3
C
H 2
C
H 2
H 3 C
Serine (Ser)
Alanine (Ala)
Glycine (Gly)
Valine (Val)
Tryptophan (Trp)
Methionine (Met)
Leucine (Leu)
Aspartic Acid (Asp)
Glutamic Acid (Glu)
Histidine (His)
Lysine (Lys)
Arginine (Arg)
Isoloucine (IIe)
Preline (Pro)
Phenylalanine (Phe)
Tyrosine (Tyr)
Cysteine (Cys)
Glutamine (Gln)
Threonine (Thr)
Polar Amino acids
Non - Polar Amino acids
Acidic Amino acidsBasic Amino acids
Asparagine (Asn)
+
–
C
C
O
O
H
NH 3
+
–
C
C
O
O
H
NH 3
+
–
C
C
O
O
H
NH 3
+
–
C
C
O
O
H
NH 3
+
–
–
–
C
C
O
O
H
NH 3
+
–
C
C
O
O
H
NH 3
+
–
C
C
C
C
O
O
O
O
H
H
NH 3
+
NH 3
+
–
–
C
CH 3
H
H 3 C
H 2 C
H 2
C
C
C
CH 3
H
H 2
C
H 2
C
H 2
C
N
H 2
C
C
C
C
C
C
C
C C
N
C
N +
H
H 2
C
N
H
C C
C
O
H 2
H 2
H 2 N
H 3 N
H 2
NH 2
H 2
H 2
C
C
C C
H 2 H 2
H 2
H 2
H 2
O
O
O
H
S
H 2
H 2
H 2
H 3 C
H 3 C
CH 3
CH
C O
O
NH 3
NH 3
+
+
NH 3
+
NH 3
+
–
C
C
O
O
O
O
H
C
H
C
H
C
C O
O
–
–
–
NH 3
+
NH 3
+
NH 3
+
H
C
C
C
C
H
O
O
O
O
CH
C O
O
–
–
–
–
NH 3
+
NH 3
+
NH 3
+
C
C
H
O
O
O
C
C C
O
O
H
H
C
O
–
NH 3
+
O
O
C
H
C
+
+
Fig. 2 Structure of twenty different amino acids
Food Biopolymers: Structural, Functional, and Nutraceutical Properties: Food Proteins…
The secondary structure comprises of localized parts of a polypeptide chain
(e.g. the α-helix or β-sheet with hydrogen bonds as their backbone. These special
structures comprise the secondary structure of protein molecules. Secondary
structure is usually due to aperiodic and periodic structures. Random coil is an
example of aperiodic structure, whereas, helical and extended are examples of
periodic structure. Stability of these structures are provided by decrease in local
free energy by the rotation of φ and ψ angles, local non-covalent interactions
between amino acid side chains, as well as hydrogen bonding between CO and
N-H groups (Nelson and Cox 2013; Voet et al. 2013).
(a). Alpha-helix proteins: The secondary structure of some proteins is essentially all alpha-helices. Myoglobin is a good example of this type. Damodaran
HO
HO
H 3 C
H 3 C
H
HS
C C
C
O
O
C
OH
H 2
NH 2
H 2 N
H 2
H 2
H
O
O
C C
C
C
C
H 2 H
NH 3
C
H 2
C
H 2
H 3 C
Serine (Ser)
Alanine (Ala)
Glycine (Gly)
Valine (Val)
Tryptophan (Trp)
Methionine (Met)
Leucine (Leu)
Aspartic Acid (Asp)
Glutamic Acid (Glu)
Histidine (His)
Lysine (Lys)
Arginine (Arg)
Isoloucine (IIe)
Preline (Pro)
Phenylalanine (Phe)
Tyrosine (Tyr)
Cysteine (Cys)
Glutamine (Gln)
Threonine (Thr)
Polar Amino acids
Non - Polar Amino acids
Acidic Amino acidsBasic Amino acids
Asparagine (Asn)
+
–
C
C
O
O
H
NH 3
+
–
C
C
O
O
H
NH 3
+
–
C
C
O
O
H
NH 3
+
–
C
C
O
O
H
NH 3
+
–
–
–
C
C
O
O
H
NH 3
+
–
C
C
O
O
H
NH 3
+
–
C
C
C
C
O
O
O
O
H
H
NH 3
+
NH 3
+
–
–
C
CH 3
H
H 3 C
H 2 C
H 2
C
C
C
CH 3
H
H 2
C
H 2
C
H 2
C
N
H 2
C
C
C
C
C
C
C
C C
N
C
N +
H
H 2
C
N
H
C C
C
O
H 2
H 2
H 2 N
H 3 N
H 2
NH 2
H 2
H 2
C
C
C C
H 2 H 2
H 2
H 2
H 2
O
O
O
H
S
H 2
H 2
H 2
H 3 C
H 3 C
CH 3
CH
C O
O
NH 3
NH 3
+
+
NH 3
+
NH 3
+
–
C
C
O
O
O
O
H
C
H
C
H
C
C O
O
–
–
–
NH 3
+
NH 3
+
NH 3
+
H
C
C
C
C
H
O
O
O
O
CH
C O
O
–
–
–
–
NH 3
+
NH 3
+
NH 3
+
C
C
H
O
O
O
C
C C
O
O
H
H
C
O
–
NH 3
+
O
O
C
H
C
+
+
Fig. 2 Structure of twenty different amino acids
Food Biopolymers: Structural, Functional, and Nutraceutical Properties: Food Proteins…