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Biology: Plasma Membrane: The Extracellular Matrix


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About this Lesson

  • Type: Video Tutorial
  • Length: 8:17
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 89 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Cell Biology (28 lessons, $45.54)
Biology: The Plasma Membrane (4 lessons, $7.92)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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Recent Reviews

This is the best
~ saraya

I enjoyed the excitement with which the extracellular matrix was presented. I find that I feel more compelled to learn when the person(s) presenting a topic are animated!!


This is the best
~ saraya

I enjoyed the excitement with which the extracellular matrix was presented. I find that I feel more compelled to learn when the person(s) presenting a topic are animated!!


If plant cells have cell walls, and that gives them structure, well, what does a plasma membrane have just below that cell wall? And what do animal cells have on their plasma membranes? In fact, what does anything have on their plasma membranes? And that brings us to the topic of the extracellular matrix. You see, cell walls are nice for structure, but they're like the girders in a building. If I were to take one of the tallest buildings in your city down, and just strip its outside material off of that so-called wall, you would just see girders, and that's the equivalent of what a cell wall is. But it's what's inside that building that really counts. It's the same thing with animal cells, and it's the same thing with all plasma membranes, particularly animal cells, because animal cells have something called the extracellular matrix. Extracellular matrix - "extra," outside of; "cellular," outside of the cell; "matrix" - kind of a network of some kind of thing.
Well, already, you're getting nervous. I hear you getting nervous out there; you're saying, "Oh, God, here's something complicated again." Well, it's not too bad. This is a picture of a typical animal cell's extracellular matrix. What are we seeing here? Let's do a quick review. Let's first of all do a quick review of the plasma membrane. You remember that the plasma membrane consists of a lipid bilayer; and you remember that the lipid bilayer has 2 tails; it has a phospholipid; and that there's a charged end - hydrophilic, and an uncharged, or nonpolar end - hydrophobic, and they're arranged in this double layer of lipids, which we call the bilipid layer.
Well, coming back to my diagram here, you can see that the plasma membrane indeed has this bilipid layer. However, when it comes to the extracellular matrix, the proteins start to become the things of the most interest - those icebergs that we refer to as icebergs floating in a sea of fat. I don't know if I like the idea of phospholipids being exactly called fat, but I like the image. Here's the image, these icebergs floating in a sea of fat. What is their function? They have 7 or 8 different functions, maybe 7- or 800 different functions. I want to tell you about one of them, and that is to act as part and parcel of this whole network of materials above the cell. So we want to talk about the components of the extracellular matrix; we want to talk about proteins, glycoproteins, proteoglycans - this is going to be some fun chemistry.
Let's talk about number one, glycoproteins. Glycoproteins, as I'm sure you know, are proteins that have starch units attached to them. You've already heard of one of those proteins, I'm sure, called collagen. Collagen is a glycoprotein that is part of the extracellular matrix. So if we take a look at this right here - in fact, do you want to know something? Half the proteins in your body are collagen; that's how important collagen is. So in this diagram here, these long, thick-looking structures are collagen fibers, and they're going to be supportive; they're going to give you lots of hold-together kinds of things, because cells are basically bags full of cytosol, watery kind of substance. You want some kind of support on there that's flexible and not rigid, say, like a wall.
So out here are the collagen fibers. But a collagen fiber is absolutely useless unless you can hold it in place. And now we come to some other things. And now we come to things called proteoglycans. Now, proteoglycans - watch, you're going to get all nervous here. You're going to say, "Well, what's the difference? Hold on, what's up with the organic chemist? Why glycans? Why are you calling one glycoproteins, one proteoglycans? You're just trying to make my life miserable." No. A proteoglycan is mostly carbohydrate. Whereas a glycoprotein is mostly protein, a proteoglycan is mostly carbohydrate; it's 95 percent carbohydrate. But the fact that it has these small polysaccharides attached to it puts it in the family other than carbohydrates, so we've got to call it something else - proteoglycans.
Well, take a look at our proteoglycans here. We have these, and they look like these branchy, tree-like structures, and they are making up a network of connected fibers, if you will, microfibers, that are forming the matrix of the extracellular matrix. So it's starting to look like a matrix. Still, nevertheless, we have to put these things together, so we have to come up with some kind of intermediate anchoring situation. So we come to what are called fibronectins. Now, fibronectins are kind of cool. Fibronectins, you can see in a second, are going to be anchoring this thing together. Fibronectins - the glue that holds it all together. So let's take a look at this. There's a nice fibronectin for you; you can see right here. And now we're getting the network shape; now we're getting the collagen fibers, attached perhaps by their starchy end to the fibronectins. You can see that the peptidyl glycans - or the proteoglycans, excuse me - are hooked to the fibronectins. But where does it hook to the cell? And that's when we come with some of these large proteins that are floating within the cell membrane itself.
Now we're going to be talking about the cell proteins themselves, and an example of this - the cell proteins, the proteins floating in the plasma membrane - we'll call those the plasma membrane proteins, because there're a lot of them, so we're going to be generic for just a second here, the plasma membrane proteins. Okay, enough generic; let's name one.
One of these would be called integrin. Integrin - it's not like it has a lot of integrity, unless you think of integrity as some integrated form. See, it's integrated into this cell membrane. And, since it's integrated into the cell membrane, it's going to attach all of this to the cell membrane. There's the lock right there. But even proteins may not, can float in this sea of fat, so we even want the proteins to be anchored. And, geez, recognize these? These are actin filaments. And so this forms this really tightly held thing that's held around the cell so that things can't just go drifting off. Function? Well, I think I've given you the idea that it's kind of important in holding the cell together, but there are some other things.
Do you realize that they've actually micromanipulated - by tugging on some of these strands, they've caused events to happen in the nucleus of the cell? That's a long ways off. That's like me pushing a button and having a bell ring 10 miles away. And yet they seem to be involved in some kind of communication from the outside of the cell to the inside of the cell. And, just as a last story, do you realize that some people have even suspected that this might be a cancer thing? I don't know if you know what cancer is; it's when cells continue to replicate over and over and over again. And some people have thought, "Well, maybe it's just a signal thing." And when cancer keeps replicating and replicating and replicating, the question you have to ask is, "Why won't they stop replicating?" Well, maybe it's simply a pressure-sensing thing that might be from the ECM, the extracellular matrix. Who knows? And I know there's been some research on that as a possible cause of cancer, some kind of extracellular matrix problem.
It goes on and on, and here's the lesson, guys: The cell membrane is an unbelievably dynamic place, and, literally, we've only seen the surface. The best is yet to come.
Cell Biology
The Plasma Membrane
Plasma Membrane: The Extracellular Matrix Page [1 of 2]

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