Question 2. The figure below is data from an experiment where we are exposing 2 types of IEC-6 small
intestinal cell lines to an extracellular sucrose solution to determine how rapidly these enterocyte cell lines
can transport large polar sucrose molecules across the apical surface of the cell membrane into their
intracellular cytosol. The phospholipid bilayer of IEC-6 cells is impermeable to sucrose hence only
facilitated transport can be used to get the sucrose into the cell. (see chapter 11). The sucrose has been
radioactively labeled with radioactive tritium H3 isotope to trace its movement and rate of transfer. The red
curve represents an IEC-6 mutant intestinal cell line that exhibits sucrose transporters with abnormal
altered conformations. The blue curve represents a wild type IEC-6 intestinal cell line with a normal
sucrose transporter. The black curve represents a Hela epithelial control cell line that does not express a
sucrose transporter protein. The x-axis shows the increasing sucrose levels the cells are being exposed to.
The y-axis shows how many sucrose molecules were transported into the intestinal cells over time; for
example, 2 molecules/second100 molecules per second. The red dots on the y axis represent the v max
and 1⁄2 v max for the red curve-mutant cell line. The blue dots on the y axis represent the v max and 1⁄2 v
max for the blue curve-wild-type cell line. The blue dot on the x axis represents the Km for the blue curve;
the red dot the Km for the red curve100 molecules/second
A. Data General outcomes shown:
1)
B. Potential mechanisms:
2)
3)
0 molecules/second
Summarize what the data shows in the figure above by writing a comparison discussion of the
three different outcomes for the 3 cell lines. (IEC-6 WT vs IEC-6 Mutant vs. HeLa)
Explain a possible molecular mechanism that could explain how the red-line (mutant IEC-6)
could have a higher Km value but still achieve a greater v max than the blue line that has a
lower Km and a lower v max
Name 3 factors that affect whether a membrane transporter exhibits a high v max or a low v
max
4)
What kinds of genetic mutations might lead to a protein having a higher v max than its wild-
type counter part. (red vs blue curve in above figure)
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