Page 1: Transport KEY
Cell A
ATP
ADP
ATP
ATP
ATP
Cell C
ADP
ATP
ATP
ATP
ADP
Cell B
ADP
ATP
The three cells shown here are in the same aqueous environment. Each symbol shown represents
thousands of actual molecules, and only those that differ between cells are shown. Use the information in
this diagram to answer the questions below and learn about transport of molecules across cell membranes
1) Fill in the table or relative concentrations below:
Cell A
Concentration
of
Concentration
of
Concentration
of
ATP Used
Cell B
Cell C
Outside of cells
5
5
5
5
1
3
1
3
0
0
3
1.5
None
1
3
n/a
2. What gradients exist between the outside environment and any of the cells? (Hint: there are 5, total)
Cells A and C have a gradient of circle (low outside, high inside)
Cells A, B and C have gradients of star (only C has higher inside than out)
3. Compare the molecular contents and membrane molecules in Cells A and B.
What molecular adaptation allows Cell B to have different contents than Cell A? Explain this.
Cell B has more of circle, because it has built a blue transport protein
that allows circle to come across the membrane into the cell.
4. Cell C is using active transport. a) Which molecule is being actively transported?
b) In which direction is it being transported: Into the cell or Out of the cell
c) Give a full and specifc explanation for what is happening.
Cell C has a transport protein that actively pumps star up its gradient.
5. Explain the usage of energy based on the data shown here.
How did Cell B use ATP for transport?
Cell B spent ATP to build the blue transport protein.
In what two ways did Cell C use ATP to allow the transport of a specfiic molecule?
Cell C spent ATP molecules to build the green transport protein AND to fuel the pumping of star .
Study at home:
a)  All three cells use a strategy called passive diffusion. Define passive diffusion in a complete sentence.
b)  Cell B uses a strategy called facilitated diffusion. Define facilitated diffusion in a complete sentence.
c)  Cell C uses a strategy called active transport. Define active transport in a complete sentence.
Page 2: Integral Membrane Proteins KEY
The four diagrams shown are different viewpoints on the same integral
membrane protein. The two cross sections are indicated by dashed lines.
Only five amino-acid R-groups are shown with colored shapes.
phospholipid tail
phospholipid head
7. Fill in this chart, using data from the cross sections and diagram above.
R-group
Most likely Most likely
Could be
hydrophilic hydrophobic either
No
Yes
Time Series
This is the substrate
molecule that is transported through
the integral membrane protein
Yes
Yes
Yes
Yes
8. If the
R-group were mutated to become hydrophilic,
what might happen to the the transport protein? Explain your
reasoning in terms of the structure and function of the protein.
A hydrophilic R-group would not interact with the phospholipid
tails stably, so the protein may not stay in the membrane correctly.
9. If the
R-group is removed, then the transport protein
moves different types of molecules across the membrane.
Give a reasonable explanation for this result.
This R-group may be on the outside of the transport protein and
have a role in binding to molecules. Removing it may remove the
specificity-checking part of the protein..
10. The time series at right shows a single molecule transporting
through an integral membrane protein. Notice the structural changes!
Why might a mutation in the
change this function? What about a mutation in
?
The transport protein must be flexible to move the substrate. Losing R-groups that contact
the substrate directly or allow tertiary structure changes may destroy transport function.