Answer
2-Mercaptoethanol reduces disulphide bonds between the cysteine molecules. The reagent does not cleave any of the peptide bonds (bonds between two amino acids) only the disulphide bonds. Thus, the disulphide bonds will be present whereever the cysteine molecules are present. Here there are two cysteine molecules in EACH polypeptide thus, there will be two disulphide bonds. Plus question, Polypeptide refers to a chain of amino acids linked by peptide bond (poly-many, thus many peptide bonds). Technically yes, polypeptides refer to a single chain of amino acids. In case of two or more polypeptides they are termed as proteins with multiple polypeptide chains. And each chain is referred to as a subunit. Although many times, polypeptide is in reference to the entire protein (not an accurate term) irrespective of whether it contains one or more polypeptide chains.
Work Step by Step
2-Mercaptoethanol reduces disulphide bonds between the cysteine molecules. The reagent does not cleave any of the peptide bonds (bonds between two amino acids) only the disulphide bonds. Thus, the disulphide bonds will be present whereever the cysteine molecules are present. Here there are two cysteine molecules in EACH polypeptide thus, there will be two disulphide bonds. Plus question, Polypeptide refers to a chain of amino acids linked by peptide bond (poly-many, thus many peptide bonds). Technically yes, polypeptides refer to a single chain of amino acids. In case of two or more polypeptides they are termed as proteins with multiple polypeptide chains. And each chain is referred to as a subunit. Although many times, polypeptide is in reference to the entire protein (not an accurate term) irrespective of whether it contains one or more polypeptide chains.
