Proteins also contain the following bond(s):

Explanation

It is correct as all three bonds: covalent, ionic, and hydrogen bonding exist in proteins. Covalent bond : The covalent bonds that connect the atoms of a single amino acid and the covalent peptide bond that links amino acids in a protein chain, covalent bonds between cysteine side chains can be important determinants of protein structure. Cysteine is the sole amino acid whose side chain can form covalent bonds, yielding disulfide bridges with other cysteine side chains: --CH2-S-S-CH2--. Ionic bond : Ionic bonds are formed as atoms of amino acids bearing opposite electrical charges are adjacent. Ionic bonds can be important to protein structure because they are potent electrostatic attractions. In the hydrophobic interior of proteins, ionic bonds can even approach the strength of covalent bonds Hydrogen bonding: The secondary structure of protein is a regular cooling or zigzagging of polypeptides caused by the hydrogen bonding of NH and C=O groups of amino acids near each other in the chain. This line is written in PTB.