This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': "During destruction in proteosomes, proteins are bound to ubiquitin by ? \nSelect and explain. \nA. Covalent bond, B. Hydrogen bond, C. Hydrophobic interactions, D. Van-der Wall's forces", 'role': 'user'}, {'content': "Answer: A \nExplanation: 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).", 'role': 'assistant'}]