Page 63 - Biology_F5

Biology for Advanced Level Secondary Schools

N-Terminus
(amino end) Gly Pro Thr Gly
H N Thr
+
3 Gly
Glu
Ser
Leu Pro Cys Lys
Met
FOR ONLINE READING ONLY
Val
Lys
Val
Leu Asp
Ala Val Arg Gly
Ser
Pro
Ala COO-
C-terminus
(carboxyl end)

Figure 1.37: The primary structure of proteins

Secondary structure of proteins: The to produce the secondary structure. The
secondary structure of proteins refers to regular pattern is due to the hydrogen bond
the regular folding pattern of β-sheets and formation between atoms of the amino acid
α helix of the polypeptide chain (Figure and backbone of the polypeptide chain. It
1.38). The linear unfolded structure of the includes components of hairs, claws, nails,
polypeptide chain assumes a helical shape and the skin.

Hydrogen bond
Hydrogen bond

(a) (b)

Figure 1.38: The secondary structure of proteins (a) α helix and (b) β plate

Tertiary structure of proteins: The of the polypeptide chain is folded into a
tertiary structure of proteins is the three- compact globular structure. The folding
dimensional structure formed by the of the polypeptide chain is stabilised by
bending and twisting of the polypeptide weak, non-covalent interactions. These
chain (Figure 1.39). The linear sequence interactions are hydrogen bonds and

Form Five Student’s Book
56