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Active Transport Lab

•    Go to http://www.mhhe.eom/biosci/qenbio/biolink/i explorations/ch03expl.htm

•    (Hołd control, right click the link, open in new window)

Pre-Lab Reading: USE THE HIGHLIGHTING TOOL TO HIGHLIGHT KEY IDEAS ON THE READINGS BELOW

•    This interactive exercise will allow you to explore how substances are transported across membranes against a concentration gradient (that is, toward a region of higher concentration).

•    By altering ATP concentrations, you will be able to speed or slow the operation of the ATP-driven sodium/potassium pump and explore the consequences for amino acid transport. Similarly, you can alter the cellular (inside) or extracellular (outside of cells) levels of amino acids and investigate the effect on how cells use ATP.

•    Because the amino acid transport channel is paired to the ATP-driven sodium/potassium pump, you will hopefully discover that both ATP and amino acid levels have important influences on the homeostasis of cells.

Pre-Lab Ouestions: Answerthese before you begin the simulation

1.    Normally, in which direction to cells usually move water or smaller molecules?

2.    In the reading above, in which direction will ATP allow molecules to move?

3.    Why is ATP needed for cellular reactions?

Lab Description:

•    On the screen you see a cutaway of a celi membranę: large proteins are embedded in “phospholipid bilayer." Remember that proteins provide channels (or openings) that some things like Sodium, Potassium and Water can freely go through.

•    The top and bottom of the screen are the outside and inside environments, respectively.

•    The floating spheres represent different kinds of molecules: the blue are sodium ions Na+

the orange are potassium ions K+

and the green are amino acids, which are the building blocks of protein.

The Yellowjagged shape is ATP and the Purple jagged shape is called ADP

Now suppose this celi requires a supply of amino acids so that it can construct proteins. It must obtain them from the outside.

Because Amino Acids are too large to ‘‘passively/freely” move through the membranę, this action requires energy for transport.

•    In our cells, the energy for this process comes from ATP.

•    Once ATP is madę available, it fuels the sodium/potassium pump, illustrated on the left edge of the celi membranę.

•    Energy from ATP, represented as a yellow star burst, is used to actively pump sodium, the blue spheres, out of the celi, and potassium, the yellow spheres, into the celi.

•    This creates a concentration gradient, with morę sodium outside the celi than inside the celi. Following the laws of diffusion, this sodium will tend to reenter the celi, distributing itself morę evenly.

Purpose

•    To explore how substances are transported across membranes against a concentration gradient using energy/ATP

•    To investigate the effects of amino acid concentration and ATP on amino acid transport.

Procedurę:

•    Click Skip Intro

•    Notę that green spheres represent amino acids, blue spheres represent Na⁺ ions, and the yellow spheres represent ATP.

Discussion: During and After you finish simulation.

1.    What element did the Amino Acids have to hitch a ride with in order to enter the celi?

2.    Amino Acids are the building blocks of what major macromolecule?

3.    Use your text or the internet and find out what the terms ATP and ADP stand for.

a. What # does the T and the D stand for in the ATP and ADP names?

4.    Discuss the major difference between passive and active transport.

5.    Construct a Microsoft excel bar graph showing the “Amino Acid Transport Ratę on the X axis” and the “Amino Acid Concentration on the Y axis.”

Procedurę:

Part A: Write results below in the No ATP expenditure box

1.    Set ATP Expenditure to 0.

2.    Click and drag the sliding indicator in the initial amino acids levels box in the lower left corner to the right to 1000 (1000/1 ratio of amino acids levels outside the celi relative to those inside.

3.    Click Start and let run for 30 sec.

4.    Repeat with initial amino acids levels set to 0.001.

5.    Record your data/observations in Data Table A.

6.    Do any amino acids enter the celi in the time interval? Why or why not?