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Biology: Phospholipids, Waxes, and Steroids

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  • Type: Video Tutorial
  • Length: 10:14
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 110 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Inorganic and Organic Chemistry (34 lessons, $51.48)
Biology: Lipids and Nucleic Acids (4 lessons, $6.93)

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 http://www.thinkwell.com/student/product/biology. 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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I don't want you to think that lipids only have a role in energy storage. Very important, these triglycerides, they do store a lot of energy. But lipids have other roles too, particularly in you and I. In fact, in all animal cells, some lipids--you'd fall apart without them. Why is that true? Well, let's take a look at it. I want to tell you a little bit about phospholipids and some other lipids that are crucial to making cell processes run and structure. But let's talk about phospholipids. You know life wouldn't exist without phospholipids. Phospholipids are a basic component of cell membranes. Everything needs a cell membrane.
Well, you and I certainly need cell membranes. They're certainly the secret to your life. Let's take a look at why these things are so important. I want to talk to you--I want to show you a phospholipid. Now, a phospholipid is called a phospholipid for a very important reason. It has phosphate in it and it is a type of lipid. You know, at first glance--let's take a look, first of all, at this space-filling model of the phospholipid over here. You see kind of a structure that looks like it has what looks like two tails and some kind of head at the top. It's important to kind of get a picture, a feel for what a molecule is before we understand what a molecule means and what it does.
Well, this is my phospholipid and there's the two tails. You know, this whole tail idea makes me think back to these triglycerides, because if you picture this thing, this one kind of had one, two, three tails coming off of a backbone of glycerol. Well, they're both lipids. Could they be kind of the same? So, at second glance we're going to find out that this is not as bad as it seems. So, I want to take a look, now, at the molecular structure of this phospholipid and take a look at the atoms that make it up.
Well, sure enough, these two tails--and we'll move this right up here. These two tails are indeed fatty acids. Now, why, you might be asking, is this particular tail bent? Did you know--I know you know this. Did you know that you need unsaturated fats to live? I'll bet you knew that. Did you know that those unsaturated fats are part of your cells? Well, now you're seeing where. You see, this particular tail of this particular lipid is bent. The reason it's bent is because right here, at this bend, there's a double bond. I'm sure you remember that double-bonded carbons, when these double-bonded carbons are in a molecule--particularly a fatty acid, they are going to cause that thing to bend. Therefore, that is going to be called an unsaturated fatty acid.
So, there's my two tails. Now, in this particular molecule, very important one, phosphatidylcholine. phosphatidylcholine, boy is that a--I'll show you where we get that name in a second. We're going to see that this is just like the triglycerides that you know and love. Why? Well, let's look. Here we go, one, two, three carbons. Look, there's an ester linkage, just like in triglycerides. So, this must be a glycerol backbone. If that's a glycerol backbone, well then, this crazy looking molecule right here must be very close to a triglyceride, except on that third situation. We're not going to find the ester linkage with the fatty acid. We're going to find something else.
Now, I know you know about functional side groups. One of those functional side groups that was so important, particularly in energy transfer, was a group called the phosphate group. Here, circled in yellow, is the phosphate group. Gee whiz, the phosphate group shows up right here, circled in yellow. So, look what we have. We have a glycerol backbone. Let's draw some lines here. We have a glycerol backbone. We have the two fatty acids, one, two. We have the phosphate group and up on top of this molecule, we have a structure called choline Phosphatidylcholine --that would be shown right here.
Now, what's so cool about this molecule is it has--so, look, look, here's what's so cool about this molecule. This end is charged. So, what we have up here is a lipid with a charged in, which is hydrophilic. Remember? Hydrophilic. Hydrophilic means water loving. Yet, down here, we have tails. Which are hydrophobic. So, the tails are hydrophobic and they're going--why are they hydrophobic? They're hydrophobic because they're completely saturated with hydrogens. Even at this point, right here, which is in the middle of the molecule. So, we are going to end up with a very interesting situation here.
If I could draw you an artist's rendition of this particular lipid--this is the way we're going to often draw these things. We're often going to draw them like this, with the tail and the bent tail. What you end up with, is a hydrophobic end and a hydrophilic, positively charged end.
Man, how important is that? Take it to the bank. Learn this. This is going to loom big in your lives as biologists. But let's not think that now we have triglycerides and these phosphatidylcholine molecules that that's it for lipids, because there's more.
Waxes are lipids. Now, probably when most people think of wax, they think of candles or beeswax. But, you know, waxes are parts of many, many living creatures. A leaf has a cuticle on top of it to prevent water loss. Do you make wax? Hum, let me think. Yeah, you do! Ear wax. Of course, earwax has a function. It's not just to be gross. Earwax is kind of the sticky stuff to keep things from getting in your ear. Ear wax, it's a lipid. Some other ones. Steroids. Now, remember, how could all these things be lipids? What's a lipid? Remember, lipids are defined by their solubility. Wax is not soluble in water. Fat is not soluble in water. Steroids are not soluble in water.
Steroids are a whole group of things. I just want to talk to you about one particular steroid. Actually, it's a sterol. Sterols are just like steroids, except they happen to have a situation where they have an O-H group. In fact, you can see in the box right now, this molecule of cholesterol. Cho-le-sterol. Hum, there's a clue. It's a steroid. Okay? Or sterol. You know, cholesterol gets a lot of bad publicity. I think it needs a good agent, because cholesterol is not as bad as it seems. We all say, "Oh, there's too much cholesterol in your diet." Cholesterol is crucial. Cholesterol--do you realize that cholesterol--well, first of all, why does it get such bad notice? It's not as bad as it used to be, because we've learned a lot about nutrition. People use to say, "Oh, don't eat so much cholesterol, it's going to cause hardening of the arteries."
Fats are what deposit in your arteries. Cholesterol, yes, it is very important to get a cholesterol test. It is very important to know the difference between these HDL's and LDL's. This is not a course in nutrition, but be aware of those things. But on the other hand--and cholesterol does lead to depositing of plaque on your arteries, but it's the plaque that's as much the problem as anything else. Those fatty deposits. Well, I'm not like a cholesterol salesman or anything and I don't own stock in butter companies, but the bottom line here is that cholesterol is indeed an important part of your living system. Here are some things cholesterol does.
Cholesterol is a component in the making of bile. Bile is a digestive juice that helps to break apart fats because fats are not water-soluble. So, you'd better have something that is fat soluble to work it and break it apart, so your enzymes can digest it. If you take cholesterol and you expose it to ultraviolet light, like from the sun, cholesterol forms something called vitamin D, the vitamin we can make in that part of our body that's exposed to the sun. Last, but not least--well, certainly, but not least, for some of us. Cholesterol forms sex hormones. That's right, testosterone and other sex hormones are indeed made--cholesterol is a precursor to those things.
So, cholesterol is one of the lipids, very important. Don't sell lipids short. I know DNA gets all the publicity and proteins, oh they're big. Carbohydrates, yeah, carbs are important. But, you know, lipids are not just meant for liposuction. Lipids are important things. Let's not forget our lipids.
Inorganic and Organic Chemistry
Lipids and Nucleic Acids
Phospholipids, Waxes, and Steroids Page [1 of 2]

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