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Lecture Comments (3)

1 answer

Last reply by: Professor Hovasapian
Fri Mar 23, 2018 6:41 PM

Post by Swati Sharma on March 23 at 10:55:09 AM

Dear Dr Rafi

Do you have lectures on Membrane Transport? and Signal Transduction Pathways as we are doing those chapter in class.

0 answers

Post by peter alabi on April 10, 2017

Hi, prof. Raffi,
Am just a little curious, and the following question may seem a little stupid.
1) knowing the fat soluble vitamins like ADEK are not water soluble, is it reasonable to ingest less of this set of vitamins as compare to water soluble vitamins, which probably get dissolve and excreted out easily?
2) In the previous lesson, you mentioned how the classes of galactolipids are found in the plants. I took the obligation to do some research, and one of the articles that I read postulated that plant uses the galactolipid to conserve phosphate for more rather important usage. Does this idea seem logical, if so, how come higher organism like vertebrates doesn't utilize a similar mechanism, I mean we need a constant supply and usage of phosphate more than plants?
3) During transformation process of e.coli in my biology lab, we used a competent cell for higher transformation efficiency, and I read that this  e.coli can be made competent by two methods, using divalent cation or electroporation, first if you don't mind explaining how this technique works in terms of the lipid bilayer.
And lastly, I think that using either divalent cation or electroporation is rather expensive, wouldn't it be better to introduce the cell to like a cold environment to facilitate the lipid bilayer to gel/solid phase, and then make some sort of incision in the cell membrane? kinda sound stupid I know.
4) Archean cell membrane lipid bilayer differ from both bacteria and eukaryotes in that they have ether linkage as compare to ester linkage, and secondly, they have L-glycerol as compare to D-glycerol in prokaryotes and eukaryotes, evolutionarily speaking would you say it significant? and does some of this structural differences account for why Archean are mostly extremophile?

Thank for the great lecture.

The Biologically Active Lipids

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • The Biologically Active Lipids 0:44
    • Phosphatidyl Inositol Structure
    • Phosphatidyl Inositol Reaction
    • Image Example
    • Eicosanoids
    • Arachidonic Acid & Membrane Lipid Containing Arachidonic Acid
  • Three Classes of Eicosanoids 20:42
    • Overall Structures
    • Prostagladins
    • Thromboxane
    • Leukotrienes
  • More On The Biologically Active Lipids 33:34
    • Steroid Hormones
    • Fat Soluble Vitamins
    • Vitamin D₃
    • Vitamin A
    • Vitamin E
    • Vitamin K

Transcription: The Biologically Active Lipids

Hello and welcome back to and to Biochemistry.0000

We have been talking about lipids for the past couple of lessons, and today, what we are going to do is close out our discussion of lipids by talking about what I call "the biologically active lipids".0003

That is not to imply that the other lipids are not biologically active, but what I mean by that is that these lipids that we are going to talk about today, they are not used as fuel storage in the fat cells or sequestered in membranes.0012

In some sense, they are sort of locked in, not really moving around much.0028

By biologically active, I mean, something that is actually free to move around, and engaged in some sort of chemistry.0032

That is all I had meant by that; I did not mean to imply that the others were not biologically active.0037

OK, let's go ahead and get started.0042

Let's see; let's go ahead and start by discussing a molecule called phosphatidylinositol.0046

Let me go ahead and draw a structure here.0054

Let me see, where should I draw it?0057

And, let me go ahead and use blue; I always like blue.0059

Let's do, no, let's go this way; No, let's go a little bit further over here.0064

C, C, C, let's go, we have our (CH3)10, CH3.0070

And then, we have our O, and then we have our other carbonyl here.0086

And then, we have (CH2)7; then we have another C.0090

We have a double bond here, then we have a CH2.0097

It looks like we have another 7 and CH3.0104

So, this is our diacylglycerol part.0107

Again, we are just attaching something to glycerol; and, of course, well, not of course, in this particular case, we are going to have a glycerophosphate so glycerol.0110

We are going to have the phosphate linkage; we will go ahead and put that in, and we have our oxygen, so this is a phosphate ester.0123

And, let's go ahead and draw in what looks like a sugar unit.0132

This is going to be the...well, I will go ahead and draw things in, and then, I will go ahead and label.0137

So, that is that; that is that.0144

That is that, and that is that, and I will go ahead and label these.0147

This is 1, 2, 3, 4, 5, and 6.0152

In this particular case, this is the numbering on this particular section.0158

So, this is phosphatidylinositol or phosphatidyl - however you want to pronounce it - inositol.0163

And, it is a glycerophosphate or a phosphoglycerol - whatever - glycerine backbone.0177

It contains a phosphate- that is what is important.0186

All these names, they make me crazy, they always have.0189

I mean, they are kind of cool in the beginning, but eventually, they start to wear on you.0192

A glycerophosphate, let's just go ahead and call it that.0195

OK, something really, really interesting happens here.0201

Now, when this molecule is activated - this is an example of its biological activity - by an extracellular stimulus - something outside the cell - binds and activates it, gets this process going - stimulus extracellular - the following reactions take place.0205

I will just go ahead and write reaction; it is not a problem.0248

"The following reaction sequence", how is that?0251

OK, the following sequence takes place.0253

OK, let me go ahead, I wonder if I should start on this page or actually go to the next page.0261

You know what, let me just go ahead and start on this page; that is not a problem, so let me go back to blue.0267

I am just going to write "phosphatidylinositol".0272

OK, this is that; this is in the membrane.0278

This is a glycerophosphate; this is one of the lipids that happens to be in the membrane.0284

Now, I will go ahead and draw a little arrow here, like this.0292

Now, and I will go ahead and do my little biochemical arrows showing things coming in and things leaving, ADP.0296

This phosphatidylinositol is actually go to be phosphorylated; 2 phosphate groups are going to be attached to it.0308

We have 2 ATPs, and 1 phosphate from there is going to attach to this.0314

Another phosphate is going to attach, so let me just go ahead and write that.0320

Phosphorylation, while in the inner leaflet- in this particular case, it takes place on the inner leaflet of the membrane; and what I mean by that is, you have, of course, the outer leaflet, and this is outside the cell.0325

And then, of course, you have the inner leaflet; this is inside the cell.0352

Inner leaflet, it is the one that is facing inside the cell, so phosphorylation while on the inner leaflet of the cell membrane.0360

What happens is this thing ends up getting phosphorylated, and what you end up with is the following molecule.0374

You end up with phosphatidylinositol 4,5-biphosphate- that is it.0380

You take a couple of the phosphate groups from ATP; we spit out ADP.0391

We take those phosphate groups, and we are going to attach them to the 4 and 5, here and here- that is it.0394

I will not redraw the structure, but it is phosphatidylinositol 4,5-biphosphate.0400

We are going to call that PIP2 in just a minute.0405

OK, now, let me go ahead and go to the next page and rewrite this, so we can continue on with this reaction sequence.0407

Phosphatidylinositol 4,5-biphosphate, which we will call PIP2, something happens that is very, very interesting.0415

I am going to draw it this way; I am going to go...actually, let me make a little more room because I want to write right above the line.0431

That is one thing, and then, go ahead and do that.0444

Here, I will do this one in red.0451

An enzyme - oops - called phospholipase - phospholipase C, actually - in the membrane - it is actually in the membrane - hydrolyzes the glycerol phosphate bond.0455

Let me just draw it out really quickly on this side, here.0496

You had your - it is really tiny - you had this, right?0500

And then, you had your phosphate bond that goes on; so, it is going to break that bond, the glycerol phosphate bond.0505

OK, actually it is not true; it is going to end up breaking this one.0514

It is going to end up breaking this one, so water is going to hydrolyze this, so water is going to come and attach to that.0520

Phospholipase C is the membrane; it hydrolyzes the glycerol phosphate bond.0525

It is actually water that is coming in, and it separates this into 2 separate molecules.0530

The first molecule that it separates into, is IP3; and this is called inositol triphosphate.0535

It is just the 6-membered ring plus the phosphate and the 2 other phosphates that are attached to it, so inositol triphosphate.0549

This IP3 is released into the cytosol.0560

Remember, we said it is on the inner leaflet?0564

Once it breaks that, the IP3 molecule just floats into the cytosol.0566

I will show you a picture of it in just a minute, so do not worry about that.0571

OK, and the other, of course, is the diacylglycerol that, it stays in the membrane.0581

I do not need to put parentheses around it; that is fine.0596

The diacylglycerol part, it stays in the inner leaflet of the membrane.0598

OK, now, here is what happens.0608

This IP3 that is now in the cytosol, it causes the release of calcium ion from the endoplasmic reticulum, from the ER.0611

I will just put ER for endoplasmic reticulum.0632

Now, the calcium ion and the diacylglycerol that is still attached to the membrane, they activate together- the calcium and the diacylglycerol - they activate an enzyme.0635

Well, we will just give the name here, protein kinase C; and we just call that PKC- very, very important enzyme.0658

PKC, protein kinase C, it begins its function of regulating further enzymes by phosphorylation.0673

Let's just recap, and then we will go ahead and take a picture of it.0703

You have this phosphatidylinositol; an extracellular stimulus ends up causing it to be phosphorylated.0707

It ends up breaking it up; actually it phosphorylates it, and so what you end up with is this phosphorylase phosphatidylinositol 4,5-biphosphate, the PIP2.0719

Phospholipase C in the membrane, it hydrolyzes the glycerol phosphate bond.0730

It breaks it up into 2 separate things: the IP3 is released into the cytosol.0735

The diacylglycerol stays in the membrane; the IP3 causes the release of calcium from the endoplasmic reticulum.0739

The calcium and the diacylglycerol activate protein kinase C, and protein kinase C starts its function of regulating further enzymes to do whatever it is that they are going to do- this signal pathway that is taking place from this phosphatidylinositol.0745

OK, now, let's go ahead and take a look at this schematically or diagrammatically here.0764

OK, here is what is happening.0771

Now, what we have done is we have this phosphatidylinositol, and it is going to end up being phosphorylated.0774

So, now, it is going to be PIP2, right?0780

We have our PIP2; this is extracellular.0783

This is outside the cell; this is inside the cell.0785

This is the membrane, right here, in green.0790

I will go ahead and go, that is fine; I will go ahead and leave it as red.0792

Now, here is what happens; the phospholipase C actually breaks off the inositol part, the polar part; and it releases it into the cytosol.0796

OK, this IP3 interacts with the receptor, the endoplasmic reticulum; and it causes calcium to be pumped out into the cytosol.0808

The calcium binds to protein kinase C; protein kinase C binds to the diacylglycerol, which was still in the membrane, and together, that combination, it starts a new series of events.0819

It starts phosphorylating enzymes which go and do whatever it is that they are going to do.0831

This phosphatidylinositol serves as a biologically active lipid.0837

It serves as a, basically, starting a series of signals to go on and do whatever it is that the cell needs to do- that is it.0844

OK, now, let's move on; let's go back to blue here.0853

Now, let's talk about another class of biologically active lipids.0859

They are called the eicosanoids, and what they are is paracrine hormones; and they act only on cells near.0865

This is what paracrine means; paracrine means they act very near the place where they are actually made.0893

They are not actually sent; they are not pumped into the blood and sent to different parts of the body like other hormones.0900

This is a paracrine hormone; it acts very, very locally.0906

That act only on cells near the region of hormone synthesis - let's just go ahead and make sure we write all this out - and not transported in the blood to remote tissues.0911

In general, when we think of hormones, that is what we are thinking about.0946

We are thinking about hormones that are pumped into the blood and sent out to other parts of the body to do whatever it is that they need to do...remote tissues and cells.0949

OK, now, let's write this one in red.0959

Their effects are both very diverse and very profound.0966

So, these eicosanoid hormones, there are a lot of things that they do, not just 1 or 2 things that they do- lots of different things that they do.0979

And, when they do them, they do them very, very profoundly; the effect is very, very deep.0988

These are not mild hormones, by any means.0993

And, let's see, what else?0999

All of them, they are derived from something called arachidonic acid.1003

OK, and we will be showing you some pictures in just a minute; and let me go back to blue for this one- membrane phospholipids.1012

Arachidonic acid is just a fatty acid- that is all it is.1022

It just has a certain length, carbon, has some double bonds in it, but it is just a fatty acid.1035

As a fatty acid, it can participate in reacting with a glycerol to form some glycerophosphate that is in the membrane.1041

So, membrane phospholipids containing the arachidonic acid are hydrolyzed when needed by an enzyme called a phospholipase A2 - to be exact - to release arachidonate.1054

And remember, when we say arachidonate, it just means it is the ionized form.1072

Arachidonic acid is protonated, arachidonate- deprotonated.1076

OK, that is what happens.1079

These eicosanoids are paracrine hormones; they act only on cells near the region of hormone synthesis, and they are not transported in the blood to remote tissues and cells.1082

Their effects are diverse and profound; they are all derived from arachidonic acid, and the arachidonic acid comes from the membrane phospholipids that contain it and are hydrolyzed when needed.1108

OK, let's go ahead and take a look here, see what we have got.1122

This is some membrane phospholipid and notice, here are glycerols.1126

Let's go ahead and mark off the glycerol part.1132

That is 1 carbon; that is 2 carbons.1135

That is 3 carbons; on one of them, we have, of course, our phosphate group.1138

And, of course, this is our polar head group, OK?1143

This looks like choline here, and then, of course, we have this one; and here, of course, we have the ester linkage, our first fatty acid, diacylglycerol.1145

Here is one of them; here is the other one.1154

In this particular case, this is our arachidonic acid right here; it has attached an ester linkage to the glycerol.1156

What it does, it actually hydrolyzes that, so it breaks this; and it ends up creating our arachidonic acid.1162

This, right here, is a membrane lipid containing the arachidonic acid.1172

And, this is our arachidonic acid right here; and, of course, once we break that, this is our arachidonic acid, our fatty acid.1190

This is arachidonic acid or arachidonate; it does not really matter.1197

Arachidonate just means you have deprotonated that, and now, you have a negative charge on it- that is it.1204

1, 2 , 3, 4, 5, 6, 7, 8, 11, 12, 13, 14, that is it- 4 double bonds.1210

1, 2, 14, 15, 16, 17, 18, 19, 20, this would be 20 carbons.1220

There are 4 double bonds, and you have a delta 5, 8, - what did we say, 11, 14 - yes, 11, 14.1230

That would be the delta notation for arachidonic acid- that is it.1237

OK, now, let's talk about the classes of the eicosanoids.1242

There are 3 classes of eicosanoids.1248

You have the prostaglandins.1261

You have thromboxanes, and you have the leukotrienes.1267

OK, let's take a look at some of these and see what we can do; and we will talk a little bit about each one.1282

Prostaglandins, thromboxanes, leukotrienes- all of them are eicosanoids.1293

They serve different purposes.1298

Let's see what we have got.1301

OK, we have got arachidonic acid, so I just wanted to put it up there, just for you to see it again.1302

Let me just write here.1309

From arachidonic acid, we end up forming - let's see what we have got here, well, let me just go ahead and write out what the names of these are.1317

Here, we have, this is a prostaglandin.1327

This happens to be prostaglandin A1, I think, yes, and notice, - well, let me just write it out - and then, over here, we have the thromboxane.1336

And then, I will go ahead and list some properties for each of these; and here, we have the leukotriene.1347

And, of course, triene, yes, you have got your conjugated triple bond, which is one of the characteristics.1357

This happens to be leukotriene before, and this is thromboxane A21363

OK, that is not A; well, that is fine, I will go ahead and write it like that.1371

OK, now, let's talk about some of these things.1376

Let's start off with our prostaglandins; let me go back to black here.1379

Prostaglandins, OK, an example of a prostaglandin, and example of a thromboxane, and an example of a leukotriene, and, of course, there are characteristic features here; so the prostaglandins, they contain a 5-membered ring.1387

There is your 5-membered ring.1410

OK, there were 2 groups originally called the PGEs and the PGFs, so the prostaglandin E series, the prostaglandin F series.1411

Now, there are other groups, there are others like the one above.1439

This is the prostaglandin A series, prostaglandin A1, prostaglandin A2, A3, whatever, just like prostaglandin E1, E2, E3, prostaglandin F1, F2, F3- that is it.1447

PGE, PGF, PGA and so on and so forth, as more and more get discovered, I guess.1457

And there are others; let me see, now, there are others.1467

Let's see what else can we say about prostaglandins.1471

OK, let's talk a little bit about what they do.1474

Prostaglandins often regulate the synthesis.1476

Again, a lot of these molecules, they do not just do one thing directly - they can - but often, what they do is they start a process, and that process has several different steps down the line.1488

You can speak of it doing this, but what it ultimately does is, maybe, this.1499

In this particular case, prostaglandins, they often regulate the synthesis of 3 prime, 5 prime, cyclic adenosine monophosphate and intracellular secondary messenger.1507

And, what we mean by secondary messenger is, let's say, from outside the cell, there is a primary messenger, some sort of a molecule that binds to the outside of the cell.1543

Something happens and it signals the inside of the cell; the inside of the cell produces 3 prime, 5 prime cyclic adenosine monophosphate, that is mediated by the production of some prostaglandin.1551

And then this 3, 5, CMP goes on to do what it does, so it is a secondary messenger.1565

It is down the line a little bit, tertiary messenger, quaternary messenger- things like that.1571

OK, let me go ahead and draw the structure, quickly, of this thing.1576

We have got our...let's see here, just so you know what it looks like.1580

Boom, boom, boom, boom, boom, boom, OK, we have our OH.1585

We have our O; let's go ahead and put the phosphate here.1592

Let's go ahead and put...this is ADNI; and you remember, the ADNI itself takes the normal numbers.1597

The sugar takes the prime numbers. This is 1 prime, 2 prime, 3 prime.1604

This is 4 prime, and this is the CH2; the is the 5 prime.1612

We have got O; that is that, and let me go ahead and put the double bond here, and I will go ahead and do that.1620

This is cyclic adenosine monophosphate 3 prime, 5 prime, if you want to be specific about where it is connected- that is it - that is prostaglandins.1628

OK, let's do some information about thromboxanes; let's go ahead and do this in blue.1641

We have our thromboxanes; now, for these, we have a 6-membered ring.1648

They have 6-membered rings containing an ether.1659

OK, they are synthesized by platelets and are involved in blood clotting, hence their name thromboxane, thromb.1669

OK, and this one is definitely good to know, NSAIDs.1705

OK, such as aspirin and ibuprofen, NSAID, non-steroidal anti-inflammatory drug.1714

An aspirin is an NSAID; an ibuprofen is an NSAID.1730

These things, they block the synthesis of prostaglandins and thromboxanes by inhibiting the enzyme prostaglandin - actually, I am going to go ahead and just write the enzyme; yes, I will go ahead and write it out, that is not a problem - H2 synthase, better known as cyclooxygenase - God, these names, just longer and longer and longer - also called C-O-X, COX.1735

These non-steroidal anti-inflammatorys like aspirin, like ibuprofen and there are several others, they block the synthesis of the prostaglandins and the thromboxanes.1799

They inhibit an enzyme called prostaglandin H2 synthase, otherwise known as cyclooxygenase.1808

This is an enzyme that you are going to talk about a lot for those of you that go on in biomedicine.1813

OK, let's say a couple of words about the leukotrienes here.1820

Let's see, do I have another page available?1824

I do, so you know what I am going to do?1828

I think I will go ahead and no, that is fine.1829

Let's go ahead and do this one in red.1834

Now, let's say a couple of words about the leukotrienes.1837

The leukotrienes, they happen to contain 3 conjugated double bonds.1843

So, if you go back to that picture, you will see that 3 of the bonds - they might have more double bonds than that, like in the picture, I think we had 4 double bonds - but 3 of them are going to be conjugated.1850

They are going to be one after the other; not directly after the other, it is going to be double, single, double, single, double single- that way.1860

That is what conjugated means; there is always a single bond between them.1866

It contains 3 conjugated double bonds; that is a characteristic feature.1869

That is the triene part, but that does not mean it has only 3.1877

It might have more; it might have there only 3, but it might have more.1880

So, 3 conjugated double bonds and let's see.1885

They are involved in inflammatory responses.1890

You know what, let me just go to the next page, let's see.1914

OK, in particular, leukotriene D4 is responsible for constriction of the airway during an asthma attack or during anaphylactic shock or anaphylaxis.1920

Let's go ahead and write it that way.1975

Oh, spelling, spelling, spelling, anaphylaxis- there we go.1980

This particular leukotriene D4, that is what is responsible, let's say, if you are allergic to nuts and your throat closes up, that is what does it- there you go.1986

OK, now, let's talk a little bit about steroid hormones; let me see here.1996

Do I have, yes, do I have them there?2002

I wonder if I should do it on the next page; yes, let me go ahead and actually write everything on the next page because we have the pictures on the next page.2005

Let me go ahead and move over here; let's talk about the steroid hormones.2015

This is another class of biologically active lipids.2020

They are lipids; they have certain biological activity as free molecules.2027

Now, they have the sterol ring structure, as you see, 1, 2, 3, 4, 1,2 ,3 ,4, 6, 6, 6, 5, 6, 6, 6, 5, A, B, C, D.2037

Remember we talked about sterol ring structure.2055

A ring structure but lack the alkyl chain on ring D.2062

So, you remember, when we look at the sterol structure, this is ring D right here.2077

OK, remember there was this long alkyl chain attached to it?2084

These have the basic structure; they have the 4 rings, but they lack that alkyl chain.2088

And as you can see, they actually have other polar groups up here.2092

Now, they are highly oxidized and reasonably polar.2096

And again, I mean, mostly we have this carbon, this hydrocarbon basic structure; but you see in oxygen here, the carbonyl group.2115

You see the alcohol group over here, alcohol group over here, alcohol group over here.2123

It is reasonably polar, at least on the 2 ends; it is reasonably polar.2128

Now, they move through the blood stream attached to proteins, and they act on cells by entering them, interacting with highly specific receptors.2133

And when we mean highly specific, we are saying that a receptor recognizes just that particular molecule.2187

OK, receptors, and triggering changes in metabolism and gene expression.2193

These are very, very, very powerful hormones; I mean, they actually change gene expression.2213

They affect what proteins are now going to be built to do whatever it is that proteins do; they change metabolism.2219

They have deep fundamental impact on what the body does.2227

OK, over here, we have - let’s do this in red – testosterone.2232

The thing that essentially makes men, men, with all of their masculine characteristics, is a steroid hormone; this is testosterone.2246

Over here, we have the estradiol, one of the primary hormones that makes women, that gives them their particular characteristics.2256

These are very, very similar; this should show you that there is actually very, very little difference between men and women.2268

It is strictly a very, very small chemical difference, essentially the same molecule for all practical purposes.2275

There it is- 2 very, very powerful steroid hormones.2284

Obviously, very powerful because as you go to puberty, men develop 1 set of characteristics, women develop another set of characteristics; and these are the hormones that induce those things.2289

OK, now, let’s go ahead and finish off this discussion by talking about the fat soluble vitamins.2298

Let’s see here; our fat soluble vitamins are...I don’t know if should write them.2306

That is OK; I will go ahead and write it over here.2315

Our fat soluble vitamins: A, D, E and K.2318

Four vitamins that the body needs- they are fat soluble vitamins; let’s go ahead and see.2332

These are isoprenoids made by the condensation - just a fancy word for putting together - of multiple units of the molecule isoprene.2339

And let’s go ahead and just do a quick structure for isoprene: double bond C.2379

I will go ahead and put the H here, and then I will go ahead and put another bond there, CH2; and should I, yes, I will just go down below.2391

That is fine; this is isoprene 1, 2, 3, 4, 5.2400

When you polymerize this molecule, when you just put 1 isoprene unit and another isoprene unit and another isoprene unit, that is what that means.2404

These isoprenoid vitamins, the A, D, E and K, they are derived from isoprene, just a bunch of units.2412

They always come in increments of 5, so 5, 10, 15, 20, 25, 30, 35, 40.2422

That is the number of carbon atoms that you are going to find in these particular vitamins.2428

OK, this one over here, this is vitamin D3.2432

I hope I have enough room to write a little bit about these things.2437

Let’s see; this is, up here is vitamin D3, also called cholecalciferol.2442

Now, this is a prehormone; in this particular form, it is not really doing anything.2457

Well, what ends up happening, so it is connected; this is converted to 1,25-dihydroxy D3.2464

What we mean by that is: one step in the kidney, one step in the liver.2487

Each one of those steps attaches a hydroxy at the no. 1 carbon, at the no. 25 carbon.2494

Now, what you have is 1,25-dihydroxycholecalciferol; this is the biologically active form of vitamin D3.2501

OK, and what this does is it regulates calcium uptake, calcium levels and uptake, intimately involved in the incorporation of calcium into your teeth and bones.2510

There is a lot about vitamin D that we actually do not know yet, and that is kind of the exciting part.2531

The field is wide open for how this thing does what it does, why it does what it does and does it do other things- very, really, very, very exciting.2536

For all of these fat soluble vitamins, we actually don not know very much about them at all.2545

OK, now let’s see here.2550

This is vitamin A; let me go ahead and go to blue for this one.2554

I am going to go ahead and just write what they are here, and on the next page, I am going to talk a little bit about them.2563

I wanted to do it on the same page, but it is not a problem; this is our vitamin A.2568

OK, and this is our, yes, I will go ahead and do it over here; that is fine.2575

This is vitamin E, and this is vitamin K.2585

OK, now, I am going to go ahead and move to a new page and write a little bit about each.2591

Let’s talk a little bit about vitamin A, and after this, we will go ahead and close off the discussion of the biologically active lipids.2597

So, it is a hormone.2606

OK, it also happens to be a visual pigment of the vertebrate eye.2610

OK, the vertebrate eye.2625

So when you see, it is vitamin C actually doing something with this protein called opsin.2630

We will discuss it later on, but it is what actually ends up sending the signals to your brain to let you know that you actually see and what it is that you see, so very, very important.2638

It is also a prehormone, and it is a bioactive form, has a hormone- is retinoic acid.2648

When you look at the molecule, you have that hydroxy at the end.2669

Well, this thing is converted to an aldehyde, and then it is converted, again, to a carboxylic acid.2678

Everything else stays the same when it is turned into the retinoic acid that becomes the active form of the hormone that goes and does what it does.2685

That is a different function from its function as a visual pigment.2692

It acts a visual pigment in one form called retinal, the aldehyde form, and then, when it is oxidized, again, to retinoic acid, it goes and does something else as it serves another hormonal function.2698

OK, let’s talk about vitamin E a little bit.2713

OK, they are called tocopherols.2720

When we talk about vitamin E, we are not talking about just 1 particular molecule.2728

I gave you a picture of one particular molecule.2733

There are slight changes in that, and that whole class of molecules that look like that, that have certain changes, those we call the tocopherols.2735

Vitamin E is like a series of molecules that are very, very, very similar.2744

And we call them the tocopherols, but we refer to it as vitamin E, so just so you know; and vitamin E is an antioxidant- very, very powerful antioxidant.2749

And antioxidants, they do one thing- they react with oxygen radicals.2761

And you remember from organic chemistry, a radical is something that has just 1 electron instead of 2 electrons, so they are highly reactive species - oxygen radicals and other free radicals, not just oxygen radicals and other free radicals - to prevent the oxidation of membrane lipids.2770

Lipids are very, very prone to oxidation very, very easily.2806

What vitamin E does is it keeps them from oxidizing, so that they can maintain the integrity of the cell- that is what it is - it runs interference.2811

These oxygen radicals and these other free radicals that are produced in the normal course of metabolism, they are going to react with lipids; and they are going to do all kinds of damage.2820

Well, vitamin E prevents that by reacting with them, so that they cannot react with the lipids in the membranes.2830

OK, and now, let’s go ahead and say - you know what, let me go ahead and use the next page - a couple of words about vitamin K, and we should be done.2837

Vitamin K, it is intimately involved with prothrombin, a blood plasma protein involved in - you guessed it - involved in blood clotting.2848

Vitamin K- very, very important for blood clotting.2888

And again, these fat soluble vitamins, we know a lot about them; but we do not know a lot about them.2893

It is a very, very fertile area of research; and I could just imagine the things that we are going to be discovering over the next 10, 20 years for these particular vitamins.2900

Thank you for joining us here at, and this closes out our discussion of lipids.2910

Take care, see you soon, bye-bye.2915