Major Ways Molecules Move Across Cell
Membrane
Name five different ways that molecules
can move across the cell membrane:
Cell Membranes and Fluid Balance
• Composition of cell membrane?
• Intracellular vs. interstitial vs. extracellular
fluid compartments
• Composition of the fluids in these
compartments?
• How is composition maintained?
• Osmolarity vs. tonicity
Extracellular
Figure taken from:
http://sorrel.humboldt.edu/~jlg21/Zoo%20310/Lab%202%20ADAM%20electrolytes/fluid%20compartments.gif
What are the major differences in composition of the intracellular and
extracellular fluid? Between the interstitial fluid and the plasma?
Figure 5-3b
1. Simple diffusion
Characteristics:
Figure 5-5
Figure 5-6
Table 5-1
2. Facilitated Diffusion
Characteristics:
Figure 5-7 (3 of 3)
Figure 5-9 - Overview
Figure 5-10
Figure 5-14
Figure 5-15
Figure 5-11
3. Primary Active Transport
Characteristics:
Figure 5-4
Table 5-2
Figure 5-16
Figure 5-17 - Overview
4. Secondary Active Transport
Characteristics:
Figure 5-18 - Overview
Figure 5-12 - Overview
Table 5-3
Figure 5-19
The glucose transporters demonstrate common characteristics of all protein
transporters:
Table 5-4
1. Similarly shaped/charged molecules can compete for transport
Figure 5-20
2. Some similarly shaped molecules can bind, but when they do, transport is
stopped (competitive inhibition)
Figure 5-21 - Overview
3. When the number of transporters is fixed, increasing the concentration of
the transported molecule will eventually saturate the transporters, and the rate
will remain at its maximum (unless more transporters are made).
Figure 5-22
Test Your Knowledge:
1. Steroid hormones pass directly through the cell membrane to activate protein
production. What type of transport is this? Why?
2. Why can urea diffuse freely from plasma into cells when most cholesterol, although
lipid-soluble, must cross a membrane by receptor-mediated endocytosis?
3. From the graph below, what transport method appears to be used for the transfer
of substance Z into a cell? Explain.
How could you test whether it was
primary or secondary active
transport?
[X]
ECF
ICF
4. Choose A if the statement refers to active transport, B if the statement refers to
passive transport, and C if it can refer to both.
• Movement of molecules from an area of high concentration to an area of low
concentration.
• Movement of molecules via proteins embedded in the cell membrane, requires ATP.
• Movement of molecules against the concentration gradient.
• A co-transporter is involved in molecule movement.
• Movement of molecules that requires ATP.
• This tends to create an equilibrium state.
Receptor mediated endocytosis
Figure 5-24 - Overview
Transepithelial transport
Figure 5-25
Figure 5-26
How do cells maintain their volume?
What factors influence their ability to maintain their
volume?
Movement of water toward the area of highest
solute concentration
Osmolarity of the cell and solution surrounding it
Tonicity of the solution outside the cell
The solution with the highest
solute concentration has the
highest osmotic pressure
Figure 5-29 - Overview
Osmolarity = total number of dissolved particles in solution
Osmolarity = molar concentration X number of particles in solution
Osmolarity of 2M glucose? 1M NaCl? 1M MgCl2?
Table 5-6
Tonicity describes the volume change that occur if a cell were placed in
that solution, after the cell has come to equilibrium with the solution.
Tonicity is not measured in units, it is only a comparative term.
Can osmolarity tell you whether a solution is hypo-, iso-, or hyper-tonic?
Table 5-7
Figure 5-30a
Figure 5-30b
Figure 5-31a
Figure 5-31b
Figure 5-31c
Figure 5-31d
Table 5-8
Table 5-9
Test Your Knowledge:
1. Which of the following solutions have the most water per unit volume:
1 M glucose, 1 M NaCl, or 1OsM NaCl ? How do you know?
Two compartments are separated aby a membrane that is permeable to water
and urea but not to NaCl. Which way will water move when the following
solutions are placed in the two compartments?
Compartment A
Membrane
Compartment B
a) 1 M NaCl
|
1 OsM NaCl
b) 1 M urea
|
2M urea
c) 1 OsM NaCl
|
1 OsM urea
You have a patient who lost 1 liter of blood, and you need to restore volume
quickly while waiting for a blood transfusion to arrive from the blood bank.
a) Which would be better to administer: 5% dextrose in water or 0.9% NaCl
in water? Defend your choice.
b) How much of your solution of choice would you have to administer to return
blood volume to normal?
Resting Membrane Potential
The relative charge difference (electrical gradient)
between the intracellular and extracellular
compartments.
What can influence the charges on the inside or outside
of the cell?
• Charge-charge interactions
• Activity of active transport pumps
• Relative concentration of each ion
Figure 5-32 - Overview
Figure 5-33
Figure 5-34a
Figure 5-34b
Figure 5-34c
Figure 5-35
Figure 5-36
Figure 5-37