In an Experiment, Erythrocyte Precursor Cells Are Incubated in a Medium

question 68

Multiple Choice

In an experiment, erythrocyte precursor cells are incubated in a medium containing radiolabeled cysteine.  These radiolabeled cysteine residues are attached to their appropriate tRNAs by the enzyme aminoacyl-tRNA synthetase.  The bound cysteine residues are then chemically modified to form alanine.  The end product of this reaction is a tRNA molecule that contains the cysteine anticodon but is mischarged with alanine.  Which of the following is most likely to occur to this alanine residue during polypeptide synthesis of alpha-hemoglobin?

• A)It will be incorporated into the polypeptide chain at a site requiring alanine
• B)It will be incorporated into the polypeptide chain at a site requiring cysteine
• C)It will be randomly incorporated into the polypeptide chain, halting chain elongation
• D)It will be rapidly cleaved off tRNA by the enzyme glycosylase
• E)It will never be incorporated into the polypeptide chain and will remain attached to tRNA

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