Chemistry Reference
In-Depth Information
Table 8.1
(continued)
Name
Structure
Optical rotation
Basic amino acids
Lysine
(+)
NH
2
H
2
N
COOH
4
Hydroxylysine
(
)
OH
NH
2
H
2
N
COOH
2
Arginine
(+)
HH
HN
N
N
COOH
3
NH
2
Tryptophane
(
)
COOH
NH
2
N
H
Histidine
(
)
COOH
N
N
NH
2
H
Fig. 8.2
Prostate group
heme
CH
CH
2
CH
3
CH
3
CH
CH
2
N
N
Fe
N
N
CH
3
CH
3
CH
2
CH
2
CO
2
H
HO
2
CCH
2
CH
2
also occur in water solutions. This is due to van der Waal interactions [
25
], because water molecules
interfere with hydrogen bonding that holds the helix together, as shown in Fig.
8.3
.
Not all proteins, however, form helical structures. If the substituent groups on the amino acids are
small, as found in silk fibroin, then the polypeptide chains can line up side by side and form sheet-like
arrangements. The chains tend to contract to accommodate hydrogen bonding and form pleated
sheets. This is called
. Such an arrangement can be parallel and antiparallel.
The identity period of the parallel one is 6.5
˚
and that of the anti-parallel 7.0
˚
.
The secondary structures of proteins do not describe completely the arrangement of these
macromolecules. There may, for instance, be sections that may exhibit some irregularity. Or, some
sections may be linked chemically by sulfur-sulfur bonds of cystine groups. There may also be areas
b-arrangement
