hydrogen bonds

-intramolecular; between O atom of C=O and H atom of -NH of amino acids, between R-groups of polar & polar/basic/acidic R groups of amino acids on same ppc

-intermolecular; between R-groups of polar & polar/basic/acidic R groups of amino acids on diff ppc

ionic bonds

-between R-groups of positively-charged & negatively-charged amino acids, in same ppc or b/w diff ppc.

disulfide bonds(strongest, only broken by reducing agent)

-between -SH groups of 2 molecules of cysteine, in same ppc or b/w diff ppc.

hydrophobic interactions

-between non-polar R groups of amino acids.

(in (aq) medium, hydrophilic R groups of amino acids face outwards towards (aq) medium; hydrophobic R groups of amino acids face inwards, shielded from (aq) medium -> protein is soluble)

Learn: H2 Biology 4 - Proteins