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Biology: The Nuclear Envelope: The Initial Tour


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About this Lesson

  • Type: Video Tutorial
  • Length: 9:18
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 100 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: An Introduction to Cell Biology (6 lessons, $9.90)

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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As a teacher, I always struggle with, "Well, where do you start learning about cells?" It's like being in a candy store with a million dollars. "Where do I start?" Yet, if you think about it, you probably know by now that, for me, it's very important to understand process, because that's what biology is about. If you understand why something is there, then you got the thing. So I don't want you guys to approach this whole idea of learning about the cell by making a list of all these complex structures and sitting down and memorizing them. That's not the way to learn biology. Sure, you're going to have to use your memory, and in this whole course, there's a lot to remember. There are probably twice as many words as the first year of a foreign language. But you know what? It's more important to understand function, because if you understand function, then you'll get the structures.
So that's where I'm going to take you now. I'm going to ask you the question. There are all sorts of different cells. There are nerve cells, and nerve cells have these real funky, crazy, long structures, and they're going to be fun to learn about. And then there are epithelial cells. They look like the shingles of a roof, and they're obviously there to protect you. And there are muscle cells, long thin cells with fibers in them whose job it is, is to contract and relax. So this is about learning function. So how am I going to tell you about the function of cells when I just right off the top of my head named 3 cells that are so completely different from each other that, how do you tell the difference, and what's up - how do they have parallel function? And the answer is that, in cells, structure and function -- in fact, in life, in living things - structure and function are always related. And there are some basic structures that give function.
So this whole theme here is structure-function, structure-function. It's what is the structure, what is its function, and, therefore, will it be in this kind of cell, or will it be in this kind of cell? And you're going to find out that there are some universal structures that are consistent in all eukaryotic cells. Why? Because, at their basis, they function the same way. What does that come down to? DNA makes RNA, RNA makes protein - the central dogma of biology. That's what it's all about. So that's where we're going to start our cell. We're going to start talking about cells with the central dogma. How does DNA do these things? Well, let's take a look. No, I lied. We're not going to talk about how DNA does these things, because we'd be here for hours. But we're going to see where DNA does these things, and a little bit about how.
Let's make believe we're diving into a cell. We've got our scuba equipment on, and we're trying to trace the path of DNA makes RNA and RNA makes protein. Where should you go? The nucleus. That's right, we should start swimming toward the nucleus, because that's where we're going to find all of the activity that governs the cell initially. Well, where would you look in the nucleus? You need kind of a roadmap, and that's why we have diagrams like this. One of the central misconceptions that people have is that the nucleus is in the center of the cell. It's not always in the center of a cell. A plant, for example, has this big old thing full of water, and it quite often pushes the nucleus over to the side. But you will know the nucleus - well, you know what you're probably going to have to do to find the nucleus? You're probably going to have to stain it and get a location, because we do have stains that will make a nucleus stand out. But we'll find that the nucleus is probably the largest structure in the cell, not volume wise, but visually, when we put some stain on there. And both animal cells and plant cells have a nucleus. There's the animal cell nucleus, and, of course, there's the plant cell nucleus.
So, as we start to swim through the cell, and we get closer to the nucleus, we start to see some interesting things. First of all, we start to see that there seems to be - we have it here as this kind of sun-like looking thing. Well, it doesn't look like a sun at all. That would be kind of cool, light at the end of the tunnel. But what it really is, is there seems to be a darker staining region within the nucleus itself, and we're going to have to see what that is. As we get closer to the nucleus, we start to see that it's not a smooth surface at all; it looks a little bit bumpy. Then, when we get closer, still, to the nucleus, we see that, "Whoa, man! There are a whole lot of these little bumpy looking things on the nucleus. And it looks like there are these - what are these? Are these like saucers of some kind?" Then we get real close and we find out that the nucleus is very, very unique.
So let's get real close to that nucleus, and here's what we're going to find. Number one thing we're going to find is that the nucleus does not have a single membrane. So I really can't say to you, "the nuclear membrane." Now that I've said that, I want you to understand I'm going to slip sometimes. I may call it the nuclear membrane, but it's really the nuclear envelope. Let's talk about that. It's the nuclear envelope. Now, does that mean that the nucleus is not surrounded by cell membrane? No, it is. But what I want you to understand is that the membrane of the nucleus is doubled.
So if you can imagine that I'm about to draw a nucleus, here's the cell, here's the membrane; so this is a bilipid layer, with proteins embedded in it, but it backs up on itself to form sections. So it's really almost like a quadruple layer of lipids, if you will. Get it? This is a bilipid layer, and it backs up and this is a bilipid layer. Then there will be another one of these right here, see, like so - this is why Thinkwell didn't hire me for my artistic abilities - and there's that.
You'll notice that there are pores within that nucleus, and that's because of the way the nuclear envelope is made. In fact, those pores are surrounded by proteins called a pore complex, a very complex complex, if you will. And that complex complex is for transport of materials into and out of the nucleus. So we start to get the idea that this nucleus is going to be a very dynamic place. You have doors in and out, and you see these things popping off of there. What we have in here is yellow structures. Well, those are actually coming out of some of these pores, and those, we find out when we look real close at them, are ribosomes. Now, we're going to talk a lot more about ribosomes, but we get the idea that something's happening in that nucleus.
So, on the edge of the nucleus, when we take a look at our nucleus and we see these bugs that seem to be coming off of the nucleus, those are not complete ribosomes, but they are ribosomal units, or subunits. In other words, they're the building blocks of a structure we're going to see later called ribosomes. Well, we start to say, "Well, where are these ribosomes coming from?" And that's where we find the function of this different agent in the nucleus. That is called the nucleolus. It means "little nucleus," but it's not a little nucleus, it's a portion of the nucleus. Nevertheless, the nucleolus is where ribosomes are formed. So the ribosomes are formed in the nucleolus, and then they leave the nucleus for destinations I'm not going to tell you about right now. So ribosomes are manufactured here. Oh, and boy, I can't even begin to tell you how that happens; I'm looking forward to that.
So ribosomes are made in the nucleolus, this section right here. So we have ribosomes being produced there, we have the nuclear envelope that ribosomes are budding off, and we have one other thing, too, I want to tell you about, it's called the - well, let's see. If you were to look on the inside of the nuclear membrane - so I'm going to redraw my nuclear membrane here, and there are my pores - we're going to have on the inside surface of the nucleus something called the nuclear lamina. Oh, it's a word, I know. You know what? Again, make it make sense. Have you ever heard of lamination? Yes, you have. Lamination like on this table here, or on your desktops? Lamination is a cover that holds things together, and that's what this is. It's a series of proteins that seem to bond that nuclear membrane and keep the nucleus having its shape.
But you know what? I haven't told you a thing about what the nucleus does yet. But at least we're inside, and now we know what's in there. Soon we'll be able to take a look and talk about this idea of the central dogma: DNA makes RNA, RNA makes protein. Stay tuned.
Cell Biology
An Introduction to Cell Biology
The Nuclear Envelope: The Initial Tour Page [1 of 2]

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