Silicon being a larger atom than carbon can form only a single covalent bond with an oxygen atom.
That allows the formation of covalent bonds between the two.
A large unknown area in pectin chemistry concerns the possible presence in vivo of covalent cross-links between pectic molecules.
Moreover, a covalent bond between two highly electronegative elements will clearly be strong.
The enzyme DNA polymerase joins the new nucleotides to each other by strong covalent bonds, forming the sugar-phosphate backbone.
