Download General Biology – Chapter 5 Notes on Active Transport Systems

General Biology – Chapter 5 Notes on Active Transport Systems (day 2)
Objectives:
1.
Recognize that these cellular transport systems require energy and therefore considered uphill
processes.
2.
Recognize and explain the sodium /potassium pump. Know that there are many other active
pump systems a cell utilizes but that we will only look at this one.
3.
Identify and articulate endocytosis and exocytosis. Endocytosis has two divisions. They are
phagocytosis and pinocytosis. Be able to delineate them.
Notes.
We will be looking at only 3 active cellular transport systems. They are the Sodium Potassium
Pump, Endocytosis and exocytosis.
Na+/K+ Pump
Because these are ions you might expect them to move through a cell membrane by ionic
channel diffusion, a passive transport system we talked about yesterday, in order to function
properly some cells require a higher concentration of sodium outside the cell and a higher
concentration of potassium inside the cell. These concentration gradients are maintained for
these to ions by the so called sodium /potassium pump. Essentially, this works just like
facilitated diffusion in conjunction with a carrier protein. The difference is that Sodium and
potassium move against the concentration gradients so that for every three sodium ions being
pump outside the cell, there are two potassium ions being pumped into the cell. Because these
ions are being pumped against their concentration gradient, the cell must use energy (ATP) to
make it happen. Refer to the reference transparency in your book. You must be able to
describe the details of this cellular transport system.
Endocytosis/Exocytosis :
For molecules and sometimes whole organisms (bacteria) that are too big to pass through the
cell membrane by facilitated diffusion, an Active process called endocytosis is employed by the
cell. If the molecule to be brought into the cell is something big like a protein or viral particle
the term we use to describe endocytosis is phagocytosis. If the molecule or particle to be
brought into the cell is smaller and there is lots of water with it, the term we use to describe
endocytosis is pinocytosis. White blood cells employ phagocytosis all the time. They actually
prefer to bring bacteria into their interior parts and destroy them there. See the diagram in
your book for differences. You must be able to spot endocytosis and exocytosis in action. Note
that exocytosis is the reverse of endocytosis and there are no addition terms to describe
exocytosis. Waste molecules and particles that are too big to pass through the cell membrane
by facilitated diffusion will be expelled from the cell by exocytosis. See the diagram below.
Note that the newly formed vesicle is actually made from a piece of the cell membrane. The molecules
brought into the cell are most likely nutrient molecules and will be delivered to the appropriate cellular
organelle for processing. Exocytosis is shown below and is nothing more than the reverse of
endocytosis.