USMLE Step 1 Physiology Review 52 10 Membrane Transport (2 of 2)

USMLE Step 1 Physiology Review 52 10 Membrane Transport (2 of 2)

On these “Gold Standard Step 1 Facts” pages you will find Free:

  • USMLE Audio Review files from our “Gold Standard USMLE Reviews”
  • Transcriptions of those files
  • And videos (as they become available)

The idea is that you can review for the USMLE online by:

  • Listening to the Audio
  • Following along with the transcription
  • Or by watching the video (if available)

If you like what you here, you can purchase the entire Gold Standard Step 1 MP3 audio USMLE review for your iPhone, iPod, or computer here.

Let’s start our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.

Play USMLE Audio MP3 52 10 Membrane Transport (2 of 2) Below

Begin 52 10 Membrane Transport (2 of 2) Transcription

There is one carrier mediated transport system that does not use metabolic energy.  What is it called?

  • Facilitated diffusion.

Why is it that facilitated diffusion does not use metabolic energy to transport substances?

  • Facilitated diffusion moves solutes down their electrochemical gradient, and so taps into the potential energy of the gradient.  An example of facilitated diffusion is the transport of glucose into red blood cells.

Another mechanism for moving substances across cell membranes is called active transport.  Active transport requires energy.  Why?

  • Active transport moves molecules against their electrochemical gradient.

Student Doctor, please pause the tape and summarize the information discussed this far about facilitated diffusion and active transport.

  • Facilitated diffusion is a carrier mediated transport system that does not use metabolic energy.  Facilitated diffusion moves solutes down their electrochemical gradient, and so taps into the potential energy of the gradient.  An example of facilitated diffusion is the transport of glucose into red blood cells.  Another mechanism for moving substances across cell membranes is called active transport.  Active transport requires energy because the system moves molecules against their electrochemical gradient.

Okay, now we’ll talk more about active transport.

Active transport is linked to energy metabolism either directly or indirectly.  Active transport is directly linked to energy metabolism through the use of what compound?

  •  ATP.

How is active transport indirectly linked to energy metabolism?  You may want to pause the tape here.

  • Active transport is indirectly linked to energy metabolism through electrochemical potential gradients of another solute. 

What are the two kinds of active transport?

Primary and Secondary active transport.

What compound provides the direct energy source in primary active transport?

  •  ATP.

What is the general name for the transport proteins in primary active transport?  Here’s a clue: they are enzymes.

  • The transport proteins are called ATPases.

What kinds of inhibitors is primary active transport especially sensitive to?

  • Metabolic inhibitors.

Secondary active transport uses potential energy.  Where is this potential energy stored?

  • It is stored in transmembrane electrochemical gradients of ions.

How are these electrochemical gradients of ions built up in the first place?  Pause the tape.

  • The gradients were established through primary active transport of ions against their electrochemical gradients.

What is the source of energy for the transport of these ions?

  • ATP.

Since ATP is the energy source for establishing the ion gradients, which in turn drive the secondary active transport of the substrate, there is an indirect link between cell metabolism and secondary active transport.

Can the physical coupling of the flow of the substrate and the ions be in the same direction across the membrane, the opposite direction, or is either scenario possible?

  • Either Scenario is possible.

The physical coupling of flow of ions and the substrate can be the same direction across the membrane or in opposite directions across the membrane. What is the term that describes when the ion and the substrate are transported in the same direction across membrane?

  • This is called co-transport.

What is the membrane protein called that mediates co-transport?

  • Symporter.  An example of co-transport is the sodium-dependent transport of amino acids into the epithelial cells like those of the gut.

What is the term that describes when the ion and the substrate are transported in opposite directions across the membrane?

  • Counter-transport

What is the membrane protein called that mediates counter-transport?

  • Antiporter.  An example of counter-transport is the sodium-calcium counter-transport in cardiac muscle cells.

Student Doctor, please pause the tape and summarize the information about mediated transport systems where there is a physical coupling of the flow of the substrate and the ions.

  • The physical coupling of flow of the substrate and the ions can be in the same direction across the membrane or the opposite direction.  It is called co-transport when the ion and the substrate are transported in the same direction across the membrane.  The membrane protein that mediates co-transport is called symporter.  An example of co-transport is the sodium-dependent transport of amino acids into the epithelial cells like those of the gut.  Counter-transport is the term that describes when the ion and the substrate are transported in opposite directions across the membrane.  The membrane protein called that mediates counter-transport is called an antiporter.  An example of counter-transport is the sodium-calcium counter-transport in cardiac muscle cells.

Now let’s talk about different forms of exo and endocytosis.

What is the process called where water and solutes are taken into the cells in vesicles formed through a process of invagination of the cell membrane?

  • Pinocytosis.

What is the process called where particulate matter is taken into the cell in vesicles formed through a process of invagination of the cell membrane?

  • Phagocytosis.

What is the process called when large and/or lipid insoluble molecules are packaged in vesicles and secreted into the extracellular fluid?

  • Exocytosis.

Student Doctor, please pause the tape and summarize the information about the different kinds of endo and exocytosis.

Pinocytosis is the process where water and solutes are taken into the cell in vesicles formed through a process of invagination of the cell membrane.  Phagocytosis is the process where particulate matter is taken into the cell in vesicles formed through a process of invagination of the cell membrane.  Exocytosis is the process when large and/or lipid insoluble molecules are packaged in vesicles and secreted into the extracellular fluid.

 

 

****END OF TRANSCRIPTION****

Want More USMLE Step 1 Review Facts?

boardprep.net

Leave a Reply