<prompt> During destruction in proteosomes, proteins are bound to ubiquitin by ?Covalent bondHydrogen bondHydrophobic interactionsVan-der Walls forces  <response>: Ans. is a i.e., Covalent bond Defective protein is first covalently attached to ubiquitin.Covalent bond is formed between glycine a-carboxyl group of ubiquitin and lysine amino group of target protein.Ubiquitinated protein is then degraded in proteosomes by ATP dependent energy dependent mechanism. Proteins are degraded by proteolytic enzymes which is energy independent non-energy dependent. 