Question

Scientists can track the movement of proteins through the endomembrane system using an approach known as a pulse-chase experiment. This experiment involves

• the “pulse” phase: Cells are exposed to a high concentration of a radioactively labeled amino acids for a short period to “tag” proteins that are being synthesized.
• the “chase” phase: Any unincorporated (not used to make proteins) radioactively labeled amino acids are washed away and large amounts of the same, but unlabeled, amino acid are added.

Only those proteins synthesized during the brief pulse phase are radioactively tagged. These tagged proteins can be tracked through the chase period to determine their location in the cell.

The data below were obtained from a pulse-chase experiment in which cells were examined at different times during the chase period. The numbers represent the radioactivity (measured in counts per minute) recorded at each of the indicated sites. The higher the number, the greater the radioactivity.

Table 1. Results of pulse-chase experiment.

	Radioactivity Levels (in counts/minute) by cellular location
Time After Pulse	ER	Golgi	Cytoplasm	Lysosomes	Extracellular Space
3 min	162	7	21	5	5
20 min	73	88	17	8	10
60 min	9	35	14	11	112
120 min	11	23	18	12	151

Question # 2: Based on the data and your interpretation, predict what is the most likely function of the cells utilized in this experiment? Explain your answer.

Answer 1

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