Membrane Transport Modeling
Materials
Paper diagrams of phospholipid bilayer and the following membrane proteins.
Aquaporin: Allow water to move from areas of higher water concentration to areas of lower water concentration.
GLUT3: Allows glucose to move down its concentration gradient.
Na+-K+ pump: Pumps Na+ out of the cell and K+ into the cell. Requires ATP.
Sodium-glucose cotransporter: Moves glucose and Na+ into a cell; Na+ down its concentration gradient, glucose against
its concentration gradient.
Physical model pieces to represent Na+ ions (small/yellow), K+ ions (small/red), water molecules (pennies), and glucose
molecules (red circles).
Procedure
Set up each scenario as described. Add the appropriate membrane protein(s) to make the movement described possible.
Draw your setup and indicate with arrow which molecules will move across the membrane and in which direction.
1. Glucose moves into a cell down its concentration gradient. (Cut out and tape the small version of the membrane
protein on the diagram below).
a. How would you characterize this membrane protein? (circle all that apply)
Pump
carrier protein
membrane protein
binds ATP
ion channel
b. How would you characterize the transport diagrammed?
Passive transport
active transport
osmosis
facilitated diffusion
Simple diffusion
movement of ions
movement of molecules
2. Glucose moves into a cell against its concentration gradient.
Na+
Na+
Na+
K+
K+
Na+
Na+
Na+
Na+
Na+
K+
Na+
K+
K+
Na+
K+
Na+
K+
Na+
K+
K+
K+
K+
Na+
K+
K+
K+
K+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
K+
K+
K+
K+
K+
Na+
Na+
K+
K+
K+
K+
K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
a. Which two membrane proteins are necessary for this type of transport?
Name
Image
1
2
b.
How would you characterize membrane protein #1? (circle all that apply)
Pump
c.
e.
f.
membrane protein binds ATP
ion channel
cotransporter
ion channel
cotransporter
How would you characterize membrane protein #2?
Pump
d.
carrier protein
carrier protein
membrane protein binds ATP
How would you characterize the type of transport enabled by membrane protein #1?
Passive transport
primary active transport
Simple diffusion
movement of ions
osmosis
movement of molecules
facilitated diffusion
secondary active transport
How would you characterize the type of transport enabled by membrane protein #2?
Passive transport
primary active transport
Simple diffusion
movement of ions
osmosis
movement of molecules
facilitated diffusion
secondary active transport
Write a short paragraph that describes how these two proteins work together to import glucose.
3. A high concentration of glucose inside the cell; a low concentration outside the cell. Insert a membrane protein
that will allow water to move across the membrane.
a. Which side has a higher osmolarity (i.e., higher concentration of solute)?
b. In the boxes, label each side as hypertonic or hypotonic. Use an arrow to indicate which direction water will
move.
4. Inside the cell, there are the same number of glucose monomers as in #3. However, these monomers are strung
together to form starch molecules (a polysaccharide). The concentration of glucose outside the cell is higher
than the concentration of starch inside the cell. Insert a membrane protein that will allow water to move across
the membrane.
c. Which side has a higher osmolarity (i.e., higher concentration of solute)?
d. In the boxes, label each side as hypertonic or hypotonic. Use an arrow to indicate which direction water will
move.
e. If you were to insert glucose transporters into the plasma membranes of #3 and #4, in what direction would
glucose move? Explain.
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