What is the sodium-potassium pump?
NARRATOR: The good molecules of Th e Cell have been on edge for days. Th e Cell has always been a vibrant place
to live and work. But that is all in jeopardy now due to a threatened walkout by the Transport Protein Workers
Union (TPWU), which has been unable to secure a satisfactory contract from the Cellular Membrane Transportation
Authority, more commonly known as CEMTA (pronounced SEM-tah). CEMTA oversees all business at the Plasma
Membrane, which forms the outer border of Th e Cell. Th e Plasma Membrane incessantly bustles with the activity of
molecules entering and leaving Th e Cell. Much of that activity is critical, and it is not known how severely a strike by
the TPWU will aff ect life at Th e Cell. Many molecules are tuned in to their local TV news stations, desperate to hear
the latest, when the following breaking news report interrupts the regularly scheduled program.
(On TV)
PHIL LIPID: Good morning. Th is is PHIL LIPID in the newsroom at Channel Two Organic News with a LIVE
Special Report. Th e Transport Protein Workers Union, or TPWU, has just held a press conference where they
announced that they will strike as of midnight tonight. Negotiations between the TPWU and CEMTA have broken
down and no new talks are scheduled at this time. CHLOE ESTEROL is standing by at the Plasma Membrane.
CHLOE, what’s the latest?
CHLOE ESTEROL: Good morning, PHIL. Talks with the TPWU have indeed broken down as of 10am this
morning. Th ose talks were reportedly marked at times by heated and occasionally emotional exchanges from both
sides. Th e TPWU has announced that they will strike beginning at 12 midnight. What that means is that all transport
through any type of transport protein, whether by diff usion, facilitated diff usion, or active transport, will be shut
down at midnight.
“Newsfl ash! Transport Proteins on Strike!” by Dianne W. York Page 2
Th e PHOSPHOLIPIDS, who are represented by a diff erent union, will remain on the job. As a matter of fact, the
PHOSPHOLIPIDS are directly behind me. You can probably hear them now because, as you know, when the
PHOSPHOLIPIDS are at work, they are constantly chattering and chanting.
(Camera zooms in on the phospholipid bilayer.)
PHOSPHOLIPIDS: (in unison) We are PHOSPHOLIPIDS. We are part of the Plasma Membrane. We let some
things pass through, but other things cannot! (chanting) Some things can pass! Other things cannot! Some things can
pass! Other things cannot! Some things can pass! Other things cannot!
(Camera moves back on CHLOE ESTEROL.)
CHLOE ESTEROL: Th e PHOSPHOLIPID chants, of course, have to do with their selectively permeable capabilities.
And as I’ve already stated, the PHOSPHOLIPIDS are expected to remain on the job in the event of a strike by the
TPWU.
Now, the TPWU is asking for better working conditions. Th ey say they work long hours without a break. Th ey say
they have diffi cult jobs, shuttling important molecules across the Plasma Membrane. And, quite frankly, they feel
they are not adequately rewarded for their eff orts. Some transport proteins have claimed that the PHOSPHOLIPIDS
receive all the attention and enjoy much better benefi ts due to their sheer numbers. Earlier, I caught up with POLLY
PEPTIDE, president of the TPWU, and this is what she had to say.
(Cut to fi lm clip of interview.)
CHLOE ESTEROL: Do you realize the dramatic eff ect a strike at the Plasma Membrane would have on Th e Cell?
POLLY PEPTIDE: (indignant) We do. But given the extreme pressure we are under, we feel this action is warranted.
Our transport proteins work hard, day and night, night and day. We are reliable. We are always there taking care
of business. We deserve better working conditions and a lot more respect for our dedication and our vital role in
membrane transport operations.
(Return to LIVE broadcast.)
CHLOE ESTEROL: PHIL, this morning, I also spoke with some of the molecules that would be aff ected by the
strike. Here’s what they had to say:
(Cut to taped fi lm segments.)
CHLOE ESTEROL: (speaking to one molecule in a large crowd): What is your name?
H2O: (caught off guard at being singled out) Uh, uh, well, I’m a water molecule.
CHLOE ESTEROL: How will you be aff ected by a TPWU strike?
H2O: Well, I use diff usion, but I’m small enough to cross the Plasma Membrane directly through the phospholipid
bilayer. So I can get back and forth that way all right. My problem will be the aquaporins. If they shut down, I could
be in trouble.
CHLOE ESTEROL: (moves toward other molecules in the crowd) Hello. Would you like to give our viewers your
opinion on the strike?
CO2: Yes, hello. I am carbon dioxide. I enter and leave The Cell by diff usion. I can pass directly through the lipid
bilayer.
CHLOE ESTEROL: (off camera) So you will not be affected by the strike?
CO2: No.
CHLOE ESTEROL: And you are?
“Newsfl ash! Transport Proteins on Strike!” by Dianne W. York Page 3
O2: (standing next to CO2) I am oxygen, and I also enter and leave Th e Cell by diff usion. I can pass directly through
the lipid bilayer, just like my friend CO2.
O2 and CO2: (in unison, with attitude) We can pass at any time! Yeah! (high fi ve each other)
CHLOE ESTEROL: (speaking to another molecule in the crowd) What is your name and how will you be aff ected by
the strike?
GLUCOSE: (somewhat snobbish) My name is GLUCOSE. I enter and leave Th e Cell by facilitated diff usion, so I
must have a transport protein to cross the Plasma Membrane. You know my transport protein recognizes me only and
no one else. It’s like I have my own personal entrance. All the glucose molecules do!
CHLOE ESTEROL: (moving closer to another molecule) And you?
AMINO ACID: (self-assured, confi dent) I’m an amino acid. I get across by facilitated diff usion. My transport protein
knows me and lets me through like that (snapping fi ngers). (proudly) No one else uses my transport protein. I’m
needed in there. A strike will be a real hardship.
(Return to LIVE broadcast.)
CHLOE ESTEROL: PHIL, obviously a strike by the TPWU will be very disruptive to cellular activities. Th at can
only be avoided with a return to the bargaining table. And at this time no meetings are scheduled. Th is is CHLOE
ESTEROL reporting LIVE for Channel Two Organic News. Back to you, PHIL.
(In the studio.)
PHIL LIPID: Th ank you, CHLOE. Now to get an objective viewpoint on the consequences of the strike, we have
with us, by LIVE feed, PROFESSOR CY TOSOL of Cell University.
(Split screen image appears with PHIL LIPID on the left and PROFESSOR TOSOL on the right.)
PHIL LIPID: PROFESSOR TOSOL, welcome. We appreciate your taking the time to speak with us today.
PROFESSOR TOSOL: Th ank you, PHIL. Glad to be here.
PHIL LIPID: PROFESSOR TOSOL, can you explain to our viewers exactly what impact a strike by the TPWU will
have on Th e Cell and its operations?
PROFESSOR TOSOL: Well, we know the strike will have a direct impact on several major functions within the
Plasma Membrane. Th ese functions include diff usion, facilitated diff usion, and active transport.
PHIL LIPID: How will diff usion be aff ected? I thought diff usion involved the PHOSPHOLIPIDS only, which are not
part of the strike.
PROFESSOR TOSOL: First of all, diff usion is the passive movement of molecules from an area of high concentration
to an area of low concentration. While it is true that diff usion can occur directly through the lipid region of the bilayer,
some, but not all, substances cross that way. Most ions, for example, require a type of transmembrane protein, called a
pore or channel. Th ey can’t move directly through the phospholipids.
Water, of course, is very important. Small amounts of water can pass directly through the phospholipids, which shift
about due to the fl uidic nature of the bilayer. Water also passes through aquaporins, special water channels that are
transmembrane proteins. In fact, this is the main route for water entering and exiting Th e Cell. Th e aquaporins are
critical for osmosis to occur.
PHIL LIPID: You mentioned osmosis. What is osmosis, exactly?
PROFESSOR TOSOL: Osmosis is the passive movement of water through the Plasma Membrane. It occurs to keep a
constant balance of water in Th e Cell relative to its environment.
“Newsfl ash! Transport Proteins on Strike!” by Dianne W. York Page 4
PHIL LIPID: You mean water will move into and out of Th e Cell depending on external conditions?
PROFESSOR TOSOL: Yes. If Th e Cell is in hypertonic (emphasizes second syllable) conditions, then there is too
much of some substance, for example salt, outside of the cell, but not enough water. Th erefore, water will leave Th e
Cell until a balance is achieved. If the situation is extreme, too much water may leave Th e Cell and it will shrivel and
die.
PHIL LIPID: We all remember the Great Dehydration scare a few years ago, when a stomach virus took its toll,
aff ecting cellular communities far and wide. So those were hypertonic conditions?
PROFESSOR TOSOL: Yes. Of course, the stomach virus was quickly eliminated, but osmosis is critical to
maintaining water balance. Now under hypotonic (emphasizes second syllable) conditions, we have the opposite
situation. Excess water fl oods Th e Cell, causing it to expand. Too much of this and Th e Cell could burst, killing it
instantly.
PHIL LIPID: PROFESSOR, the scenarios you are describing seem to mean dire consequences for Th e Cell unless the
strike is averted.
PROFESSOR TOSOL: Yes, PHIL. I would have to agree with your assessment. Ideally we want isotonic conditions,
which is a nice balance of water on both sides of the Plasma Membrane. To achieve that, the aquaporins must function
properly.
PHIL LIPID: Is there anything else our viewers should know?
PROFESSOR TOSOL: Well, if the strike does proceed, facilitated diff usion would be another lost service.
PHIL LIPID: What processes does facilitated diff usion entail?
PROFESSOR TOSOL: Facilitated diff usion is the passive movement of molecules across the Plasma Membrane that
is aided by transport proteins. Without facilitated diff usion, large and important molecules like glucose and the amino
acids can’t get into Th e Cell.
PHIL LIPID: Th at would be very bad, for obvious reasons. PROFESSOR, everything you’ve discussed so far has been
described as a passive movement. Why do you call them passive?
PROFESSOR TOSOL: Because they don’t require energy. Diff usion, facilitated diff usion, and osmosis are all
passive because Th e Cell does not use energy to drive the process. Active transport, however, does require Th e Cell to
expend energy, usually in the form of ATP. Energy is needed whenever a substance must move “uphill,” against the
concentration gradient. Th at is to say, from an area of low concentration to an area of high concentration.
PHIL LIPID: And does active transport require the use of transport proteins?
PROFESSOR TOSOL: Yes, it does. So this is yet another function that would be lost during the strike.
PHIL LIPID: What kinds of molecules cross the Plasma Membrane by active transport?
PROFESSOR TOSOL: Th e sodium-potassium pump, for one, is a transport protein that needs ATP to run. Th at’s a
type of active transport that moves sodium and potassium ions across the Plasma Membrane. Regulation of sodium
and potassium concentrations is critical to the survival of Th e Cell.
PHIL LIPID: Well, this has been very enlightening. It seems that Th e Cell could be in a great deal of trouble if the
transport protein workers are on strike. Th ank you for your time, PROFESSOR TOSOL.
PROFESSOR TOSOL: You’re very welcome, PHIL. Glad I could help.
(Split screen dissolves. Return to single frame.)
PHIL LIPID: We now return to reporter CHLOE ESTEROL, LIVE at the Plasma Membrane with an important
update.
“Newsfl ash! Transport Proteins on Strike!” by Dianne W. York Page 5
CHLOE ESTEROL: PHIL, just moments ago, the TPWU and CEMTA announced that they will return to the
bargaining table at 3pm. Th ere is hope that they will be able to reach an agreement and avert the proposed strike that
could have a devastating outcome for Th e Cell and its molecules.
PHOSPHOLIPIDS: (chanting, in the background) Some things can pass! Other things cannot! Some things can pass!
Other things cannot!
CHLOE ESTEROL: As you know, the situation here at the Plasma Membrane is very tense. Many molecules could be
stranded on either side of the Plasma Membrane if there is a strike. Molecules are worried about how they will get into
and out of Th e Cell, if the transport proteins are not operating.
PHOSPHOLIPIDS: (chanting, in the background) Some things can pass! Other things cannot! Some things can pass!
Other things cannot!
CHLOE ESTEROL: Here is a molecule on its way into Th e Cell now. You look concerned. How will you handle the
strike?
O2: Being an oxygen molecule, I can cross the Plasma Membrane. Th e problem is what kind of chaos will I fi nd once
I get inside Th e Cell? I mean, cellular respiration requires both myself and GLUCOSE. If GLUCOSE can’t get in,
how can I do my job?
CHLOE ESTEROL: PHIL, a lot is resting on the continuation of talks between the TPWU and CEMTA. Th is is
CHLOE ESTEROL Channel Two Organic News.
PHIL LIPID: Th ank you, CHLOE. With us now is MR. GENE NOME, spokesperson for Th e Cell. (Talking to
GENE NOME.) Th ank you for joining us today.
GENE NOME: (nods in response) Please call me GENE.
PHIL LIPID: OK, GENE it is. GENE, what is Th e Cell doing to avert this strike?
GENE NOME: PHIL, Th e Cell is acutely aware of the magnitude of the situation. We have been present during talks
with the TPWU, and we will again return to the table as talks resume shortly.
PHIL LIPID: Specifi cally, what must happen for the TPWU and CEMTA to reach a compromise and avert this strike?
GENE NOME: Th e Cell has always held a strong belief in fairly compensating all of our cellular workers. We believe
that it is in the best interests of all involved that a strike be averted. And we fi rmly believe that an agreement can be
reached in time for that to happen.
PHIL LIPID: GENE, thank you again for your valuable time.
GENE NOME: (nods in response) You’re welcome, PHIL.
PHIL LIPID: Once again, the TPWU and CEMTA have announced a return to the bargaining table in an attempt to
avert a strike scheduled to begin at midnight. We will continue to bring you LIVE updates as information becomes
available.
(Return to regularly scheduled program.)
NARRATOR: At 9:35 pm, a LIVE press conference was broadcast to the molecules of Th e Cell announcing a
resolution between the Transport Protein Workers Union and the Cellular Membrane Transportation Authority.
PHIL LIPID: We have just heard a LIVE press conference where it was announced that the strike has been called off .
Th e TPWU has agreed to a contract with CEMTA. Reporter CHLOE ESTEROL is LIVE at the press conference.
CHLOE ESTEROL: PHIL, the TPWU has announced that they will sign a new contract with CEMTA. All of the
details of that contract have not been released yet, but according to GENE NOME, spokesperson for Th e Cell, a
major part of the agreement involves a collaboration between Th e Cell and CEMTA to ensure that the transport
NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
“Newsfl ash! Transport Proteins on Strike!” by Dianne W. York Page 6
•
Title image adapted and licensed from © -=Lexx=- – Fotolia.com, ID#19513423. Case copyright held by the National Center for Case Study
Teaching in Science, University at Buff alo, State University of New York. Originally published December 28, 2011. Please see our usage
guidelines, which outline our policy concerning permissible reproduction of this work.
proteins receive the attention and recognition they deserve in all biology textbooks. So, in eff ect, biology students
everywhere will learn about the vital role of transport proteins in the Plasma Membrane and their importance to
operations in Th e Cell.
Th is is CHLOE ESTEROL reporting LIVE on the edge of the Plasma Membrane. Channel Two Organic News.
THE END
•
Questions
1. What is the meaning behind the PHOSPHOLIPIDS’ chant?
2. Why is H2O concerned about the aquaporins shutting down? What are aquaporins and how are they involved in plasma membrane transport? In addition to the use of aquaporins, what is another way H2O can cross the plasma membrane? Is this second way suffi cient? Explain your answer.
3. Both GLUCOSE and AMINO ACID claim to have a special relationship with their respective transport proteins. What is the basis for their claims?
4. Could O2 and CO2 make the same claim as GLUCOSE and AMINO ACID? Why or why not?
5. Th e movement of oxygen and carbon dioxide into and out of the cell is called gas exchange. Which two body organ systems are involved in gas exchange? Which type of plasma membrane transport is used for gas
exchange? Is this method best? Explain your answer.
6. PHIL LIPID and PROFESSOR TOSOL discuss the Great Dehydration. Explain what you think occurred during the Great Dehydration. Why are sports drinks recommended to prevent, or treat, dehydration?
7. In an interview with CHLOE ESTEROL, O2 says that if GLUCOSE can’t enter Th e Cell, then cellular respiration would be aff ected. Explain the connection between glucose, oxygen, and cellular respiration.
8. What is the sodium-potassium pump? How does it work? Which body organ system depends on sodiumpotassium pumps to function?
9. What are transport proteins and why are they important? What would happen to Th e Cell if the transport proteins went on strike?
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