Scientists can track the movement of proteins through the endomembrane system us
ID: 266491 • Letter: S
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
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 #3: The graph below conveys the information above in a different format. what are the advantages and disadvantages of presenting the information in this way? The figure legend has been omitted Pulse time 100 Extracellular Space ER 0 - - Golgi 60 120 40 Time after chase (min.) 3 20Explanation / Answer
From the table and the figure it is clear that the protein labelled was extracellular secretory protein. But here the table and the figure drawn cannot be corelated properly. The table shows the values of accumulation of radioactively labelled proteins in different compartments of cell like endoplasmic reticulum, golgi, lysosome, cytoplasm and
in extracellular space. But in the graph shows only data of ER,golgi and extracellular space. Lysosomal and cytoplasmic portions are missing there. Putting all of them in a single graph would make the entire figure clumsy.
Another error is that the graph here is not representing tabular datas properly. For example in 60 minutes there is more accumulation of tagged proteins in golgi than ER. But the figure it is showing opposite. But the advantage of using linear graph than table is easy visual understanding and easy comparison. Another advantage is more time points can be drawn in a graph. Above the graph shows values at 40 minutes time after pulse. But these values are not shown in table. So a graph can show the pathway or fate of transcribed proteins in a more visually appealing way (particularly in such cases of labelling experiments).
A better representation of the tabular data is possible through proper diagram which has not been done here.
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