AP Biology Organic Compounds

Welcome to Educator.com.0000

In today's lesson, we are going to be discussing organic compounds, and living organisms are made up of organic compounds.0002

Organic compounds are compounds that contain carbon.0011

Compounds that do not contain carbon are known as inorganic compounds, and the field of study of organic compounds is called organic chemistry.0015

An example of an organic compound would be something such as methane/CH₄, whereas water/H₂O is considered inorganic.0026

Now, even though water is inorganic, it is obviously very important to biology and to life.0038

That is not to say that living organisms do not contain or need inorganic compounds, but they are mostly composed of organic compounds.0044

And that is going to be our focus of today's lecture.0051

A couple of exceptions though, although carbon monoxide and carbon dioxide contain carbon, these two are generally classed as inorganic.0056

There is a couple other exceptions as well, but these are the important ones that contain carbon but generally, scientists refer to as inorganic.0066

Alright, starting out with the basics, organic compounds have a carbon skeleton.0076

A carbon skeleton is a backbone of carbon, and then, the carbon atoms are bonded to other atoms.0085

This carbon skeleton could be various lengths.0093

It could be just a couple carbons long. It could be many carbons long.0099

It could be branched, so it could have carbons attached to this first linear section of carbons.0102

The atoms that are attached to carbon could be various atoms, but there are certain ones that are particularly important in biology0113

and that we are going to keep returning to, and those are hydrogen, oxygen, nitrogen, phosphorus and sulfur.0120

These are the ones we are going to focus on, although, of course, living organisms do contain other elements,0141

and use other elements such as calcium or magnesium, trace elements such as iron, that we discussed in the previous lecture.0147

But, for organic compounds, carbon plus these other five elements are the ones that you are going to see occur the most.0156

Now, carbon is a very versatile element, and that makes it an excellent basis for biological molecules.0164

Let's think back to the structure of carbon, and that will explain its versatility.0174

Recall that carbon has six electrons. That means that it has two in the first electron shell, and that shell is filled.0179

That shell only holds two.0191

It has four electrons in the second shell, so its valence shell contains four electrons.0192

And that leaves four empty spots, four more electrons to get to a total of eight for a full valence shell.0198

Therefore, it needs four electrons to fill its valence shell, and it can fill that shell in various ways.0204

It could form four single bonds with other elements such as, say, hydrogens here and then, the other carbon next to it.0217

So, that is one way it could fill. It is sharing four electron pairs with other atoms.0229

Another possibility is that it could form double bonds, so remember with CO₂, carbon forms two double bonds,0236

one with one oxygen, one double bond with one oxygen molecule and oxygen atom, and then, another double bond with the second oxygen.0245

That, again, gives a total of four total shared electron pairs, and they will fill the valence shell of carbon.0254

This ability to share so many electron pairs gives carbon a lot of versatility,0260

and alas, just from a few different elements, a huge range of molecules that can be produced, and these molecules are the basis of life.0267

Hydrocarbons are molecules that consist only of carbon and hydrogen, so this would be an example of a hydrocarbon.0278

And the entire molecule is not necessarily a hydrocarbon. It could be a situation such as a protein.0299

There are actually other large biological molecule where there is a chain or just a section of hydrocarbons.0307

So, there can be a large biological molecule that has various different atoms on it, but one section of it is hydrocarbon.0313

And that hydrocarbon section is going to be non-polar.0321

Hydrocarbons are non-polar, and they form regions of molecules that are non-polar as well.0324

You could just have a hydrocarbon. You could have a larger molecule with just a hydrocarbon section on it.0331

We are going to focus on four classes of organic compounds today, actually two today and then, two in the next lecture.0340

but overall, four important classes, but before we do, we need to go on and discuss the concept of isomers.0348

Isomers are molecules that have the same molecular formula, but they differ in their structure; and there are three types of isomers.0355

This first type here is called structural isomers. The second type right down here shows geometric isomers.0364

And the third type is enantiomers, or these are sometimes called optical isomers.0376

Let's start with the structural isomers.0384

Well, first, to be isomers, they need to have the same molecular formula.0386

So, let's ensure that that is correct, 1, 2, 3, 4 carbons, so C₄, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 hydrogens,0390

C₄H₁₀, 1, 2 , 3, 4, same here, it has 4 carbons, and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 hydrogens.0400

These have the same molecular formula. They have the same atoms, same number, same ratio, but they are obviously different.0409

What makes them different is that they have different bonding partners.0416

These are arranged differently. They are covalently bonded to different atoms.0421

The difference between a pair of structural isomers is that one isomer has different bonding partners than the other,0427

OK, different bonding partners, same atoms arranged differently in terms of covalent bonding.0436

Looking at this molecule on the left, this is butane. This, right here, is butane, whereas this molecule is called isobutane.0448

And you will notice that butane just has this linear arrangement with the carbon skeleton, 1, 2, 3, 4 in a row.0463

whereas looking at isobutane, there are three carbons, and the middle carbon is covalently bonded to the fourth carbon.0474

And this difference in structure gives the molecules different properties.0481

The properties of a molecule are determined not just by the atoms that make it up but by the arrangement of those atoms.0485

That is an example of a structural isomer.0491

Now, let's look at geometric isomers.0495

I take a look at these and I see that "OK, I have 1, 2, 3, 4 carbon atoms, 3, 6, 7, 8 hydrogen- C₄H₈",0498

over here, 1, 2, 3, 4 carbon, 3 hydrogen, 6, 7, 8- same formula.0509

And then, I look, and each carbon is bonded to a carbon, and then, that carbon in turn the 3 hydrogens,0517

and then a hydrogen down here, and then, a CH₃ group and a hydrogen and double bond at the carbon.0524

And if I look over here, it is the same thing.0529

Each carbon is double bonded to the other carbon and to the CH₃ group and to a hydrogen.0531

They have the same bonding partners. They have the same atoms, but you can see that they are different.0540

And what makes them different is the spatial arrangement of the atoms around a double bond.0545

Double bonds are inflexible. The atoms cannot just rotate around that bond.0552

Now, if this were a single bond, this could actually rotate, and then, the hydrogen could flip up here.0557

The CH₃ group can then go down here, and then, these would not actually be isomers.0562

But because this double bond is inflexible, these are, sort of, held in this position.0567

And you can see in this example, this molecule right here, these two CH₃ groups are on the same side,0572

whereas here, the CH₃ groups are on a different side, and what we call this is the cis isomer.0578

If the two groups are on the same side in the geometric isomer, that is the cis isomer,0584

the isomer where the two groups are in opposite sides is called the trans isomer.0590

Alright, so we have structural isomers. That was the first type of isomer.0596

Geometric, and then, the third is enantiomer or the other name for it is optical isomers.0600

And the name optical isomer helps to remember what it is because what it is is a mirror image.0607

Let's say that up here the blue is hydrogen, and then, maybe this brown is a carboxyl group, COOH.0617

In the center, we had a carbon bonded to a hydrogen, a carbon bonded to a carbon in turn bonded to these.0626

Maybe down here, I have what is called an amino group. This could be NH₂ bonded and then, another atom, another group, say, CH₃.0632

OK, now, the purple in the other molecule is, again, CH₃, this brown, COH, and the green, NH₂.0646

And if you look at these, they are mirror images, and they are not superimposable.0658

Because this is in 3-dimension, so maybe these two are coming out towards you, and it is similar to your left and right hands.0662

Your left and right hands are mirror images of each other, and they are not superimposable; and it is the same idea here.0671

And in fact, we call these left and right-handed molecules, and they are known often as L and D-enantiomers.0676

L stands for the Latin levo, which is left and then, D from the Latin dextro or right.0687

Optical isomers are left and right-handed forms of a molecule, and this difference is extremely important in science and biology.0702

For example, in pharmacology, it matters a lot sometimes which enantiomer you are working with.0711

There are some medications where one of the enantiomers is very effective, and the other is useless.0718

Or both may have a use, but they are different, or one may even be harmful.0724

Certain medications are a mix of the L and D-enantiomers, and one enantiomer is useful.0730

And the harmless one is in there as well, does not cause any problems but does not help either.0737

For Parkinson's disease, one treatment is a medication called L-Dopa.0742

L-Dopa is the L-enantiomer, and it is effective in treating Parkinson’s, whereas the D form of this molecule is not.0749

The next concept we are going to cover, before we get on to some0760

of the large molecules that you will be working with in biology, is that of functional groups.0763

You have already seen a couple of functional groups.0769

When I just wrote out the COOH, that is a carboxyl group. NH₂ is an amino group.0771

Now, we are going to go ahead and treat this formally.0778

Groups of atoms that are especially important in determining a molecule's behavior are called functional groups.0780

And by determining its behavior, these are parts of the molecule that takes part in chemical reactions.0786

They determine what types of chemical reactions a molecule would participate in, and they also help to determine the shape or structure of the molecule.0795

And there are certain ones that you will see over and over, so you should become familiar with these and recognize them when you see them.0807

So, recall that hydrocarbons contain only carbon and hydrogen.0813

However, in many molecules, one or more of these hydrogens is replaced by a functional group.0821

Let's go over some of the common functional groups.0829

The first one is called an amino group, and as its name suggests, you will see these in amino acids.0832

This is NH₂, and this line here indicates a bond, so this would be bonded to the carbon skeleton.0840

This is the functional group, and it is bonded to the carbon skeleton.0853

Sometimes, one of the carbons in the carbon skeleton is part of the functional group, and we will see that in a second.0855

But for now, the amino group, again, is found on amino acids, and it can actually act as a base.0861

It can pick up a hydrogen ion and become NH₃⁺ in a solution.0868

OK, that is amino group.0877

The second group, which I already mentioned in the last slide, is a carboxyl group.0879

This carboxyl group is COOH, and this carbon could be part of a longer carbon skeleton.0884

Carboxyl groups are found in organic acids such as acetic acid. It has a carboxyl group.0894

Acetic acid is what is found in vinegar. It is what makes vinegar acidic.0902

In solution, the hydrogen ion could be lost, and then, this could become COO^- and then a lost hydrogen.0907

These are also found on amino acids.0920

The next group, OH, is called a hydroxyl group. Hydroxyl groups are found on alcohols such as ethanol.0923

That ol-ending tells you it is an alcohol, and these are polar.0937

These are polar because of the preference of the electron pair to its oxygen, the more electronegative oxygen compared to the hydrogen.0946

The bond between the oxygen and the hydrogen, the electron pair favors more electronegative oxygen.0962

Right here, we have CH₃ group. This is called a methyl group.0975

CH₃ or a methyl group is found in what is called methylated compounds, and it could be attached to a carbon; or it could be attached to another atom, actually.0981

Here, we have what is called a carbonyl group.0992

And there is two subsets of how we name molecules containing these groups depending on where this group is within the larger molecule.0994

If, let's say, we had a carbonyl group right here embedded within the carbon skeleton, this would be called a ketone.1006

If the carbonyl group is in the middle within the carbon skeleton, it is called a ketone.1028

The other possibility is that this group is on the end. Here, the end carbon contains the carbonyl group, and this is what we call an aldehyde.1036

Again, there is two breakdowns for carbonyl groups: ketones, the carbonyl group is within the carbon skeleton. If it is on the end, it is an aldehyde.1054

An example here would be acetone. Aldehyde would build something like a formaldehyde.1064

Finally, we get to phosphate group, and you are going to see C phosphate groups throughout biology.1072

For example, cell membranes contain a phosphate group.1078

This is a phosphorus bonded to four oxygen atoms, and one of these oxygen atoms is bonded to the carbon skeleton.1083

You will notice that this is a charged molecule that to this oxygens have a negative charge, and therefore, it is hydrophilic.1093

Alright, now that we have talked about the basics of organic chemistry,1107

we are going to go on and talk about the four major classes of organic compounds that we are going to be discussing and focusing on in biology.1111

These four groups include carbohydrates, lipids, nucleic acids, and proteins.1121

In this lecture, in addition to covering the basics of organic compounds, we are going to be going over carbohydrates and lipids.1135

Nucleic acids and proteins are covered separately in the following lecture.1142

Carbohydrates are macromolecules. Macromolecules, just like their name, tells you macro and molecule are large molecules.1148

These are a vital source of energy for cells, and they have the molecular formula C, some X, H₂O to Y,1158

and some multiple of H₂O, various multiples of that.1171

What this is saying is that hydrogen and oxygen are found in the 2:1 ratio. That is what this is actually saying.1177

Hydrogen to oxygen, the ratio is 2:1.1185

As I mentioned, carbohydrates are an important energy source. They are found in many foods such as breads, rice, potatoes.1191

These are all rich in carbohydrates, and you will often hear people talk about simple carbs versus complex carbohydrates.1199

And we are going to talk about that as well, and that has to do with the structure of the carbohydrates.1205

Carbohydrates are sugars, and they can actually be categorized as monosaccharides, disaccharides and polysaccharides.1210

Starting out with just a simple situation, monosaccharides, mono meaning one, sacchar meaning sugar.1218

Monosaccharides have the formula CH₂On, so some multiple of CH₂O, some multiple of that, where n is usually either 3, 5 or 6.1228

If n is 3, you will end up with C₃H₆O₃, and if you have a 3-carbon sugar like this, it is known as a trios. 3-carbon sugar is a trios.1249

A 5-carbon sugar is called a pentose, and a 6-carbon sugar is called a hexose sugar.1263

Let's go ahead and look at a couple different types of monosaccharides: glucose and fructose.1272

Glucose is the main form in which you will find sugar stored in animals. Fructose is the type of sugar that you will find in fruits.1278

Glucose is produced by plants via photosynthesis, and then, this can be broken down by cells to release the energy to fuel various cellular processes.1289

Glucose and fructose have the molecular formula C₆H₁₂O₆, and you should recognize this.1298

This formula will come up, and you should recognize it as a formula for this particular type of monosaccharide, which is a hexose sugar.1304

Let's go ahead and look at the two forms.1314

You will see that there is a linear form and a circular form, and the reason for this is that in aqueous solution, sugars often exist in their ring form.1317

So, this is the same sugar. These two are the same, and these two are the same, but this is just the linear form.1328

And then, in aqueous solution, it would form this ring, so you will often see these molecules written in their ring form.1333

And to keep track of things, we number the carbons, and we start at the top: 1, 2, 3, 4, 5, 6.1341

And then, we can refer to groups on the different carbons based on their number.1348

2 is here, 3. This is 4, 5 and 6, so these are 6-carbon sugars. These are hexoses.1355

Now, when this turns into a ring, we need to keep track and see where all these carbons go, and again, we number them 1, 2, 3, 4, 5 and 6.1364

And we can do the same over here with fructose.1378

All it is, is that this forms a ring, and you could see the 6 sticking up right here, same thing with fructose.1382

Now, another thing that I mentioned before is the location of the carbonyl group, this C double bonded to O.1396

Looking first at glucose, you will see that this C double bond OH right here, this carbonyl group is on the end.1406

And recall that, when it is on the end, we call that an aldehyde, so this is actually what we call an aldehyde sugar or an aldose sugar. Glucose is an aldose sugar.1413

Fructose, a carbonyl group is here. It is embedded within the carbon skeleton, so this is what we call a ketose or ketone sugar so ketose sugar.1427

And again, that is based on the location of this C double bond O: on the end in glucose, embedded within the carbon skeleton on fructose.1440

Those were monosaccharides. Monosaccharide means that there is just one sugar.1453

There is just one subunit.1460

Monosaccharides can join together to form a disaccharide. Disaccharide, just like the name suggests, two sugar subunits.1462

These are both known as simple sugars.1474

If you have more than two subunits, it is called a polysaccharides, and those are complex carbohydrates.1480

So, simple carbs or simple carbohydrates, simple sugars and then, polysaccharides are known as complex carbohydrates.1487

The formation of disaccharides or polysaccharides occurs when two monosaccharides join through what is called a dehydration reaction.1499

Dehydration means you lose water, and that is exactly what happens here.1512

If you looked at just two glucose molecules, this was a single glucose molecule and then, a second glucose molecule,1518

they bond together through this dehydration or condensation reaction.1527

Before they were bonded together, what you would have had is on this molecule and a hydrogen up here, the hydroxyl group right here.1531

And each of these corners/points, that is a carbon.1545

This is a carbon. This is a carbon.1549

This is a carbon. This is a carbon.1551

For simplicity, we often do not write this out.1553

In the ring form, it is just convention that each of these is a carbon.1555

You have a carbon here, and it is bonded to a carbon, the oxygen next to it, the next carbon, the hydrogen and this hydroxyl group.1560

The same thing for the other glucose, so there was an adjacent glucose, free, not bonded to the next glucose - this is before the reaction - that looks like this.1574

Then, what happened is one of these glucose molecules - this was glucose, free glucose, monosaccharide, this is glucose - one of these loses an OH.1586

The other loses a hydrogen, so it loses HOH or H₂O, in other words, water. That is why it is called a dehydration reaction.1599

With this gone, this OH, and this hydrogen gone, you are left with these two bonded together via this remaining oxygen, and that is what you see here.1612

One of these has lost an OH, a hydroxyl group. The other has lost a hydrogen, and that remaining oxygen, then, links to adjacent sugar molecules together.1623

This bond is called a glycosidic bond. Adjacent sugars are held together by a glycosidic bond formed through a condensation reaction.1634

And that forms, which has two subunits. They are both glucose, and this is a disaccharide.1646

It is also known as a simple carbohydrate or simple sugar.1653

Lactose would be another example. This is a sugar that is found in milk.1659

And this is formed between glycosidic linkages between one molecule of glucose and a second molecule of another sugar called galactose.1663

Sometimes, you will hear people talk about lactose intolerant. They are not able to have dairy products like milk or cheese.1674

And the reason is, they lack an enzyme called lactase.1683

When we talk about enzymes, you will see that ase-ending tells you it is an enzyme, and here ose tells me this is a sugar.1689

So, lactase is the enzyme that breaks down lactose, and if somebody is lacking this, they do not have very much of this,1696

they are not able to break down this sugar, and that causes them to have gastrointestinal symptoms when they have dairy products.1701

OK, what we started out with down here with the maltose was glucose, C₆H₁₂O₆, but we actually had two of those.1712

Actually let's move over here where there is a bit more room, so C₆H₁₂O₆.1732

But, we actually had two of these, and these came together to form C₁₂H₂₂O₁₁ plus one molecule of water.1739

So, 2 x 6, that gives you 12 carbons. 2 x 12 is 24, and we have 22 here in this disaccharide,1753

then, the other two in the water molecule that was lost in the dehydration reaction, and then, 2 x 6 is 12.1760

We have 11 oxygens here within the disaccharide, and then, 1 oxygen, again, lost as part of that water molecule.1768

Now, sugars in plants and animals and organisms are usually stored in more complex forms than just monosaccharides and disaccharides.1776

And then, they are broken down as needed to provide energy.1785

The formation of the glycosidic bond is through what is called this dehydration or condensation reaction.1790

The opposite is hydrolysis. Hydrolysis comes from hydro meaning water, and then, lysis meaning to break.1799

To break the glycosidic bond, hydrolysis reaction occurs, and what happens is it adds water.1812

Water is added to the bond, and it releases this bond; so that you, then, have two glucose molecules back.1820

A maltose is formed through the dehydration reaction forming glycosidic bond.1829

And then, hydrolysis can add water and turn these into two separate glucose molecules.1835

Sugar are actually stored in more complex forms, and those forms would be starch usually in plants.1842

And then, in animals, what you will see is glycogen. Sugar is stored in the form of glycogen.1852

Looking at this starch molecule, you will see that it is much more complex than the disaccharide, and it is, in fact, a complex carbohydrate.1862

This is formed through glycosidic bonds that are joining more of these monosaccharide subunits and joining them here in a branched form.1874

Looking at starch, there is a couple different kinds of starch.1885

One type is amylose. Another type, which is shown here, is amylopectin.1889

This is amylopectin, and you will see that it is branched.1898

Another thing to note is that the 3-dimensional structure of starch is helical.1901

We call starch and glycogen, we call these polymers, so when there is a chain formed from similar identical subunits, these are known as polymers.1907

A bunch of subunits of glucose join together. They can be a linear form and then, form a helix, that is amylose.1919

It can branch off and form amylopectin.1927

Glycogen is even more highly branched than amylopectin. Again, it is a form of polysaccharide.1930

It is a way of storing sugar in animals, and glycogen and starch can both be broken down through hydrolysis to release the energy as needed.1938

Glycogen is found primarily in the liver and in muscle cells.1948

Sugars are used for quick energy, so they are rapidly available; but they are also rapidly depleted.1954

And that is why we have other forms of energy store such as fats, which we will talk about shortly, and proteins.1961

In addition to being forms of energy, carbohydrates also have a structural function.1970

I was focusing here on starch and glycogen and the glucose subunits as forms of energy, and they are obviously important for that.1978

Carbohydrates are also used to form structures in plants and animals.1990

If starch is an energy form, glycogen is an energy form, what are the structural forms?1997

Well, plants contain cellulose, and we will go into detail about cellulose in the plant lecture.2001

But for now, you should just know that this is a form of carbohydrate that is found in the cell walls of plants.2010

Plants do not have skeletons obviously, so for support and for protection, instead, they have cell walls.2015

And cellulose is a polymer made of glucose subunits that is the primary component of the cell wall of plants. It is different, though, than starch.2023

It is not the same as starch. It is not the same as glycogen.2031

It has a different 3-dimensional structure.2035

Cellulose actually are glucose monomers that hydrogen bond, and they form what is called microfibrals.2038

It is a fibrous type, more of a fiber-like or cable-like structure, a microfibral.2045

Humans cannot digest cellulose, so what we call roughage is a part of the plant that passes through the human GI tract undigested.2054

And that is the cellulose, so especially with raw fruits or raw vegetables, apples, figs, carrots or anything, these contain roughage.2064

And although, they are not digested, they are important for the GI tract because when we call them roughage, it is actually a pretty accurate name.2073

It actually scrapes against the walls of the intestine, and that stimulates mucus secretions from the cells in the intestine.2080

So, even though cellulose is not digestible, it is an important part of the human diet.2088

OK, structural forms of carbohydrates: one is cellulose, another is chitin.2094

Chitin is found in the cell walls of fungi such as mushrooms, and it also makes up the exoskeleton of arthropods such as crustaceans, also insects.2100

This is found in exoskeletons, and it is also found in the cell wall of fungi.2112

Again, we will revisit this all in detail in later lectures, but just give me some examples now to make this more concrete.2117

Two functions of carbohydrates: one is as an energy store in form such as glucose, maltose, lactose, starches, glycogen.2125

The second: structural functions, and this could be cellulose found in the cell walls of plants,2136

chitin, which is found in the cell walls of fungi as well as the exoskeletons.2141

Alright, carbohydrates were the first class of large biological molecule.2147

The second group of large biological molecules that we will be discussing is lipids, and these are actually a diverse group of molecules.2153

But they are classed together because they are all non-polar or hydrophobic.2160

Example of lipids are fats, oils, phospholipids and steroids as well as waxes.2165

We are going to be focusing on fats, phospholipids and steroids because these are the most important in terms of biology.2170

If you glance down here at a typical fat, this is a triglyceride or fat, you will see that it has this large regions of hydrocarbons.2179

These long hydrocarbon chains are regions that are non-polar.2189

I mentioned that earlier in this lecture that hydrocarbons are non-polar, and non-polar molecules contain regions of hydrocarbons.2194

Let's go ahead and see how a triglyceride molecule is built.2204

It is built from one glycerol and three fatty acid molecules, so one glycerol plus three fatty acid molecules equals one triglyceride.2208

Glycerol is an alcohol, and each glycerol, then, bonds with the three fatty acids.2219

And you can see where these are linked, if you look first at the glycerol molecule and then, this OH group.2230

And then, you will see CH₂, O, and then, it is bonded to the first fatty acid, the second fatty acid and the third fatty acid.2242

And this is, again, a dehydration reaction.2252

If you look here, you will see OH and then, C double bond O, OH.2255

I look over here, there is two oxygens and this carbon and a carbon here.2264

What has happened is through the dehydration reaction, two hydrogens and one oxygen had been lost.2271

The dehydration reaction, loss of H₂O and then, the glycerol molecule ends up bonded to the fatty acid via this oxygen.2281

This type of linkage is called an ester linkage. As ester linkage is a bond between a hydroxyl group and a carboxyl group.2294

A bond between these two type of functional groups that is formed is called an ester linkage.2311

Here, we have three ester linkages between one glycerol and three fatty acid molecules.2315

As you can see the formation of that between these two molecules to here, adding two more groups gives you the triglyceride2322

and the tri meaning three, so three fatty acid chains on the one glycerol molecule.2331

Fats can be divided up into two different categories.2338

And you have probably heard these categories or read them on nutrition labels: saturated and unsaturated.2340

When we say that a fat is saturated, we mean that the carbons are saturated with hydrogens. Think of it that way.2355

Another way of looking at it is there are no double bonds between the carbons.2364

This is a saturated fat shown here because all the carbons are held together by single bonds, and each carbon is saturated with hydrogens.2372

It is holding as many hydrogens as it can. It is bonded to as many hydrogens as it can be.2382

Unsaturated, there is one or more double bonds between the carbons.2387

For example, if I inserted a double bond here, I would have to, then, get rid of this hydrogen.2395

This carbon is no longer fully saturated with hydrogen. It has a double bond to the adjacent carbon.2402

You will often hear people say "oh, saturated fats are the bad ones, and unsaturated are the good ones".2414

Let's talk about some differences between these two types of fats.2419

Saturated fats have no double bonds, and they often come from animals. They are animal fats.2424

They are solid at room temperature, and the molecules that comprise them pack together tightly.2434

And that has to do with the fact that they are just single bonds. An example would be butter.2445

Unsaturated fats usually come from plants. They are liquid at room temperature, and they do not pack together as tightly.2454

The reason for that is this double bond creates a kink.2467

You will often see the fatty acid tails, so if this is the glycerol, you will sometimes see these fatty acid tails shown as zigzags just like this.2471

That is their structure and so on.2492

Now, when there is a double bond, it introduces an even larger kink, so it would go out to the side like that.2501

For example, this might be a saturated fat, and then, if there is a double bond, it actually kinks the molecule so that it is not just a straight tail like this.2508

And you can see that if this is kinked, these could not pack together as tightly. They could not pack together with adjacent fat molecules.2518

This double bond causes the kink in the fatty acid tails that does not allow them to pack together as tightly.2526

And that is also why they stay liquid at room temperature. They do not solidify because they are not packed together as well.2532

A diet that is high in saturated fat increases a person's risk of atherosclerosis.2540

An atherosclerosis is the formation of plaques in the blood vessels, and these plaques decrease the flow of blood to the vessels, and it can result in heart disease.2544

Often, unsaturated fats are thought of as the healthier fats. An example would be canola oil.2554

Canola oil is mostly unsaturated fat, whereas butter is mostly saturated fat.2561

Now, fats are a way for organisms to store energy. I mentioned that animals can store glucose as glycogen, and then, they can break it down.2568

But that gets rapidly depleted. For longer term storage, a very efficient way to store energy is as fat.2578

Adipose tissue serves as a way to store energy, and it also serves as insulation and protection.2585

These are just some functions of lipids. Another function of lipids in addition to fats would be to form phospholipid.2594

We talked about one type of lipid, which is fat. The second type we are going to talk about is phospholipids.2604

Cell membranes are made up of phospholipids, and let's go ahead and look at the structure.2610

Here, we have the glycerol molecule again, and we have fatty acid tails; but this time, we only have two.2615

Instead, this third carbon, instead of being bonded to a third fatty acid, it is bonded to a phosphate group.2629

This phosphate can, in turn, be bonded to another functional group, and that will determine which type of phospholipid that you have.2640

But the basics for phospholipids are glycerol, two fatty acid tails and a phosphate group.2650

The phosphate plus the glycerol, this region is hydrophilic, so we say that phospholipids have a hydrophilic head.2658

And then, we look at the fatty acid tails, and we say that they have hydrophobic tails.2669

Because there is one section that is hydrophilic and another that is hydrophobic, we say that this molecule is amphipathic.2681

An amphipathic molecule has a hydrophobic region and a hydrophilic region.2687

Because of this amphipathic nature, phospholipids self-aggregate in the bilayers, and they do this in order to shield these hydrophobic portions from water.2708

What you will end up with is phospholipid bilayers where the hydrophilic heads face outward, and the hydrophobic tails are sequestered inside.2720

This is the hydrophobic portion, and it is sequestered inside from the water.2731

The interesting thing about this is, well, the structure is that it can serve as a barrier.2736

And it does serve as a barrier so that the cell membrane only allows certain substances to pass through.2744

And, in particular, hydrophobic substances will pass much more easily through the cell membrane because of this phospholipid bilayer's non-polar central region.2749

Hydrophobic molecules tend to pass through the cell membrane more easily than the hydrophilic molecules.2760

This is an introduction of phospholipids, and we are going to do a lecture later on in the course on cell membranes2765

and talk more about the structure, as well as about substances that pass through the cell membrane easily and those that do not.2771

Alright, so far, we have discussed fats and phospholipids, which are both types of lipids.2780

The third type of lipid we are going to discuss is steroids. Steroids are lipids that contain a carbon skeleton of four fused rings.2785

This basic ring structure is called cholesterol, and it is the building block for other steroids.2794

Hormones are substances that allow cells to communicate with and affect cells a distance away.2806

For example, a hormone would be estrogen or testosterone. These are both hormones.2813

Many hormones are steroids. These two are steroids, so estrogen and testosterone are examples of steroid hormones.2824

That means that they have this basic four fused ring structure, but there are different functional groups attached.2834

The bonding is a little bit different, so alterations are made to these that give each one a unique structure and very different function and properties.2841

And if you think about it, you can see that this is going to be pretty non-polar. It is going to be hydrophobic.2851

And that is actually very helpful for a hormone because it allows them to pass into the cell.2856

Again, we are going to revisit this topic later on when we talk about cell membranes and cell communication.2862

But for right now, you just need to know that hormones are often steroids, and that steroids are based on a cholesterol ring; and they are non-polar.2867

Alright, today, we have discussed two of the four classes of large biomolecules.2876

We have discussed carbohydrates and lipids, and we are going to continue on in the next lecture to talk about nucleic acids and proteins.2882

But before we do, let's do a few examples to reinforce your knowledge.2889

Example one: what type of isomer is each of the pairs of molecules shown below?2894

Remember that isomers have the same molecular formula, so let's just double check and see that that is true.2899

I have two carbons here, two bromines and two hydrogens.2906

On the other molecule, I also have two carbons, two bromines, two hydrogens- same molecular formula.2911

The first type of isomer is a structural isomer, so let's see if they have the same bonding partners.2918

Each carbon is double bonded to another carbon on both of these, and then, each carbon is bonded to bromine and hydrogen- bromine, hydrogen.2925

Same here, but they are not the same geometrically. They differ in their spatial arrangement.2933

These are not structural isomers since they have the same bonding partners. In fact, they are geometric isomers, and one clue to this is the double bond.2939

This inflexible double bond holds these molecules in a certain conformation where the two bromine molecules are on one side in this isomer.2949

This would be the cis isomer, and they are in the opposite sides in the other isomer, and this is known as the trans isomer.2958

That is my first set of molecules. The second set, I am going to double check and make sure that the molecular formulas are the same:2965

1, 2, 3 carbons, 1, 2, 3, 4, 5, 6, 7, 8 hydrogens, 3 carbons, 8 hydrogens, 1 oxygen.2971

Over here, 1, 2, 3 carbons, 1, 2, 3, 4, 5, 6, 7, 8 hydrogens, 1 oxygen, so these have the same molecular formula.2981

Next thing to check: are the bonding partners the same?2993

Here, I have a linear arrangement of carbon, carbon, carbon and then, oxygen.2996

Here, I have the three carbons, but instead of the oxygen being bonded to a carbon on the end, the oxygen is bonded to a middle carbon.3002

Therefore, the covalent bonding is different, and these are, in fact, structural isomers.3011

These are both forms of propranolol. This is actually propyl alcohol, while this one is isopropyl alcohol.3020

And again, these different isomers are going to have different properties.3033

The first example was geometric isomer. The second is an example of structural isomers.3040

Second example: identify the functional groups on the molecules below.3046

Let's go ahead and just look at the linear. This shows glucose and both its forms.3052

We can look at it in either, but I am going to look at the linear; and this is actually an amino acid.3055

Let's look at all three of these and just see what we can identify. One thing that we can identify here is a hydroxyl group.3063

Here, on the end, this has a carbonyl group, and remember that when it is on the end like this, we often call it aldehyde.3077

If it was in the middle, we would have called it ketone group.3085

Over here, I have COOH right here, so this group is a carboxyl.3093

The carbonyl is C double bond OH.3104

I have identified hydroxyl, carbonyl, carboxyl, and then, I have an NH₂ here. NH₂ is called an amino group.3108

What do I have here? CH₃, I have two of these, and these are methyl groups, OK?3121

Here are some of the various function groups that I have identified: carbonyl, particularly an aldehyde, hydroxyl, amino, carboxyl and methyl.3131

Example three: the structural formula for galactose, a sugar, is shown below.3146

Based on the number of carbons, what type of sugar is galactose. Is it a ketose sugar or an aldehyde sugar?3152

OK, this is galactose, 1, 2, 3, 4, 5, 6 carbons. Therefore, this is a hexose sugar.3158

To determine if it is a ketose or aldehyde sugar, I need to look for the carbonyl group, and that is right here.3169

It is on the end carbon. Therefore, this is an aldehyde sugar.3175

So, galactose is a hexose sugar, and it is an aldehyde sugar.3182

Example four: what class of molecules does this molecule belong to? Why?3189

Well, you probably immediately notice this characteristic structure of four fused rings, and this molecule, therefore, is based on cholesterol.3195

Therefore, it is a steroid.3206

Notice, though, that the bonding, the functional groups, are a bit different than on cholesterol.3209

And in fact, this happens to be estradiol, which is a form of estrogen.3215

You can see that change in the structure just a bit gives it very different function and unique properties.3219

That concludes this lecture on organic compounds at Educator.com, and I will see you again next time.3227