Saturated fats, unsaturated fats, and trans fats | Biology | Khan Academy

Summary

This educational script explains the molecular structure of triglycerides, highlighting the implicit presence of carbon and hydrogen atoms. It distinguishes between saturated fats with no double bonds, monounsaturated fats with one, and polyunsaturated fats with multiple double bonds. The script also clarifies the difference between cis and trans configurations in unsaturated fats, emphasizing the health risks associated with artificial trans fats, which are now banned in many places due to their detrimental effects.

Takeaways

• 📚 Triglyceride molecules are often represented in shorthand in chemistry and biology, with carbon atoms implicit at the vertices of the chain structures.
• 🔍 Every carbon atom is assumed to have four covalent bonds, with any unoccupied bonds filled by hydrogen atoms.
• 🔑 The presence of double bonds in triglycerides indicates an unsaturated fat, which can have different physical properties compared to saturated fats.
• 🍯 Saturated fats, like butter, are solid at room temperature due to the maximum hydrogenation and lack of kinks from double bonds.
• 🚫 Trans fats are artificially created and are considered very unhealthy, with detrimental effects on health, leading to bans in some regions.
• 🌱 Naturally occurring unsaturated fats are typically in the cis configuration, which causes the fat molecules to bend and be less dense.
• 🔄 The cis configuration of double bonds in unsaturated fats leads to a more liquid state at room temperature due to the difficulty in packing these molecules closely.
• 🔄 The trans configuration, where hydrogens are on opposite sides of the double bond, does not create kinks and can be solid at room temperature.
• 🍳 The process of hydrogenation intended to create a solid fat from liquid oils can also convert cis double bonds to trans, forming unhealthy trans fats.
• 🧪 The distinction between saturated, monounsaturated, and polyunsaturated fats is based on the number of double bonds present in the triglyceride molecule.
• 🌟 Nutritional debates aside, the script emphasizes understanding the chemical structures and properties of fats rather than outright labeling them as 'good' or 'bad'.

Q & A

What is the shorthand representation of triglyceride molecules?

In the shorthand representation, the carbon atoms are implicit at each vertex of the chain, and if there's no letter at the end of the chain, there's also a carbon atom there. Hydrogen atoms are assumed to fill any remaining covalent bonds on each carbon atom.

Why are the carbons and hydrogens in triglyceride molecules often not explicitly shown?

They are not explicitly shown to simplify the diagram of these large molecules, making it easier to visualize and understand their structure in chemistry, biology, and organic chemistry.

What is the difference between saturated and unsaturated fats in terms of their molecular structure?

Saturated fats have only single bonds between carbon atoms, allowing for the maximum number of hydrogens, making them solid at room temperature. Unsaturated fats have one or more double bonds, leading to fewer hydrogens and a kinked structure, making them liquid at room temperature.

Why are saturated fats typically solid at room temperature?

Saturated fats are typically solid at room temperature because their molecules can pack closely together without kinks due to the absence of double bonds, allowing for a more dense structure.

What is the role of double bonds in the structure of unsaturated fats?

Double bonds in unsaturated fats create kinks in the fatty acid chain, preventing the molecules from packing closely together, which makes unsaturated fats more likely to be liquid at room temperature.

How are monounsaturated fats different from polyunsaturated fats?

Monounsaturated fats have one double bond, while polyunsaturated fats have multiple double bonds. The presence of more double bonds in polyunsaturated fats makes them even more likely to be liquid at room temperature.

What is the significance of the cis and trans configurations in unsaturated fats?

The cis configuration causes a bend in the fatty acid chain due to the hydrogens and carbon chains being on the same side of the double bond, while the trans configuration has them on opposite sides, which can affect the physical properties and health implications of the fat.

Why are trans fats considered unhealthy?

Trans fats are unhealthy because they are often produced artificially and do not occur naturally. They can have negative health impacts, including raising bad cholesterol levels and increasing the risk of heart disease.

How are trans fats formed, and why were they used in food products?

Trans fats are formed through a process of hydrogenation, where hydrogens are added to unsaturated fats to make them more solid. They were used in food products like shortening and margarine because they were cheaper to produce, had a longer shelf life, and provided a desirable texture.

What is the difference in molecular structure between cis and trans fats?

In cis fats, the hydrogens and carbon chains are on the same side of the double bond, causing a bend in the molecule. In trans fats, they are on opposite sides, which straightens the molecule and can lead to a structure similar to saturated fats.

Outlines

00:00

🧪 Understanding Triglycerides and Fats

The script introduces the concept of triglycerides, which are large molecules often simplified in diagrams by omitting carbons and hydrogens, which are implicitly present. Each carbon atom is assumed to have four covalent bonds, with any unoccupied bonds being filled by hydrogens. The paragraph distinguishes between saturated fats, which have only single bonds and are typically solid at room temperature, and unsaturated fats, which contain one or more double bonds, leading to a kinked structure and a liquid state at room temperature. The difference between cis and trans configurations of unsaturated fats is also introduced, with cis fats naturally occurring and being healthier, while trans fats, often artificially produced, are considered harmful to health.

05:01

🔍 The Difference Between Cis and Trans Fats

This paragraph delves deeper into the structural differences between cis and trans fats, explaining how the rigidity of double bonds leads to different spatial arrangements of the carbon chains. Cis fats, with their bent structure due to double bonds, are more likely to be liquid at room temperature and are generally healthier. In contrast, trans fats, which have a straighter structure due to the trans configuration of the double bonds, are solid at room temperature and are associated with negative health effects. The paragraph also discusses the historical use of trans fats in food products as a replacement for butter and their subsequent banning due to health concerns.

Keywords

💡Triglycerides

Triglycerides are a type of lipid composed of a glycerol molecule attached to three fatty acid chains. In the video, triglycerides are the main focus, with the speaker explaining their molecular structure and the difference between saturated, monounsaturated, and polyunsaturated fats. The video script uses a shorthand way to represent these large molecules, highlighting the implicit presence of carbon and hydrogen atoms.

💡Carbons and Hydrogens

Carbons and hydrogens are the primary elements that make up the fatty acid chains in triglycerides. The script explains that in diagrams, carbon atoms are implicit at each vertex of the chain, and hydrogens are assumed to fill the remaining covalent bonds of each carbon atom, except where double bonds are present. This understanding is crucial for grasping the structure of fats and how they differ in their physical properties.

💡Saturated Fat

Saturated fats are triglycerides in which the fatty acid chains contain only single bonds between carbon atoms, allowing for the maximum number of hydrogen atoms to be attached. The video describes saturated fats as typically solid at room temperature, like butter, and contrasts them with unsaturated fats, which have double bonds leading to different physical properties.

💡Unsaturated Fat

Unsaturated fats are triglycerides that contain one or more double bonds in their fatty acid chains. The presence of double bonds reduces the number of hydrogen atoms and introduces 'kinks' in the fatty acid chain, which affects the fat's physical state and health implications. The video script distinguishes between monounsaturated and polyunsaturated fats based on the number of double bonds.

💡Monounsaturated Fat

Monounsaturated fats have one double bond in their fatty acid chains. The video script uses this term to describe a type of unsaturated fat that has fewer kinks than polyunsaturated fats due to the single double bond. Examples from the script include fats that are still relatively straight due to the single point of unsaturation.

💡Polyunsaturated Fat

Polyunsaturated fats contain multiple double bonds in their fatty acid chains. The video explains that these multiple double bonds lead to more pronounced kinks in the molecular structure, making the fat less likely to be solid at room temperature. This term is used to illustrate the difference in physical properties and health effects compared to monounsaturated and saturated fats.

💡Cis and Trans Configurations

Cis and trans configurations refer to the spatial arrangement of atoms around a double bond. In the video, the speaker explains that most naturally occurring unsaturated fats are in the cis configuration, which leads to kinks in the fatty acid chain. In contrast, trans fats, which are not typically found in nature, have a straighter structure due to the trans configuration, where the hydrogen atoms are on opposite sides of the double bond.

💡Trans Fat

Trans fats are a type of unsaturated fat that, due to their trans configuration, have straighter molecular structures similar to saturated fats. The video script discusses how trans fats are often artificially created through the hydrogenation process and are associated with negative health effects, leading to bans in many places.

💡Hydrogenation

Hydrogenation is a chemical process where hydrogen is added to unsaturated fats, converting some of the cis double bonds into trans double bonds. The video script explains that this process was initially thought to be a healthy alternative to saturated fats but has since been recognized as unhealthy due to the creation of trans fats.

💡Nutritional Debates

Nutritional debates refer to ongoing discussions and controversies about the health effects of different types of fats. The video script touches on these debates, particularly regarding the health implications of saturated fats, and emphasizes the consensus that trans fats are harmful, despite some debates about the role of fats in nutrition.

Highlights

Triglyceride molecules are diagrammed with carbons and hydrogens implied rather than explicitly shown.

Each pointy part of a triglyceride chain represents an implicit carbon atom.

Carbon atoms are assumed to have four covalent bonds, with extra bonds being filled by hydrogens.

Triglycerides with no double bonds are called saturated fats and are typically solid at room temperature.

Saturated fats are associated with being solid and are commonly found in foods like butter.

Unsaturated fats have one or more double bonds, leading to fewer hydrogens and a kinked structure.

Monounsaturated fats have one double bond, while polyunsaturated fats have multiple double bonds.

The presence of double bonds in unsaturated fats causes a kinked structure, affecting their physical state.

Cis and trans configurations determine the shape and properties of unsaturated fats.

Cis configuration causes the chain to bend due to the rigidity of double bonds.

Trans fats are created by hydrogenation and have a straight chain due to the trans configuration of double bonds.

Trans fats are not typically found in nature and are considered unhealthy.

The process of creating trans fats involves changing some cis double bonds to trans double bonds.

Trans fats were once considered a healthier alternative to saturated fats but are now known to be detrimental to health.

Many states and countries have banned trans fats due to their negative health impacts.

Trans fats are considered to have properties similar to saturated fats but with additional harmful effects.

The debate around the health effects of saturated fats continues, but trans fats are universally recognized as harmful.

Transcripts

- So I have drawn four different

triglyceride molecules over here.

And some of you might be saying,

"wait I thought triglycerides they involve

"all of these carbons and hydrogens and oxygens".

Well I see the oxygens over here

but where's all of the carbons and hydrogens?

And my answer to you is that they will be implicit.

This is a short-hand way of diagramming out

these large molecules.

And you'll see this many times

when you take chemistry, biology, organic chemistry.

And what's happening here is that

each of these pointy parts of this chain,

each of these vertices there's implicitly a carbon.

There's a carbon there, there's a carbon there.

There's a carbon there.

And there's also,

if we don't put a letter at the end of the chain,

there's also a carbon right over there.

So implicitly there's a carbon there,

there's a carbon there, there's a carbon there.

Now you might also be wondering

what about the hydrogens?

Well we assume that every carbon has four covalent bonds.

And so if there's extra covalent bonds

for each of these carbons,

we assume that those covalent bonds are with hydrogen.

So for example, this carbon right over here,

it has two covalent bonds.

So the other two covalent bonds must be

must be with hydrogens.

Same thing for this carbon right over there.

It must be bonded to two hydrogens.

This carbon, the way its drawn, we only

explicitly see one covalent bond.

So there must be three covalent bonds.

There must be three covalent bonds to hydrogens.

So the carbons and hydrogens are all there.

They're just implicitly there.

Now you might notice, and actually, if you don't notice,

I encourage you to pause

and think about what the difference is

between this triglyceride, this triglyceride

this triglyceride and that triglyceride.

And it might jump at you pretty quickly.

What jumps at you is this triglyceride has

no double bonds.

This one has one double bond.

This one has several double bonds.

And this one also has several double bonds.

But these two are also different

and we're gonna think about the way that they're different.

You might immediately see that this one

kinda kinds and curves

while this one is able to stay relatively straight.

And actually that is the main difference.

And we're gonna talk about it in a second

why that is.

But first lets talk about this one.

When you have all single bonds

one way to think about it is that

you have put as many hydrogens onto

these carbon chains as you can.

Or another way of thinking about it is

we have saturated this fat with hydrogens.

And that's why this is called a saturated fat.

A saturated, this is a saturated fat.

This is something that you might have heard of.

This is referring to things like butter.

They've a lot of different fats that we tend to

associate with being solid at room temperature.

And the reason why they're solid at room temperature

is because this are all bonded to these hydrogens.

There's no kinks for them to do to the double bonds.

These are able to be relatively dense.

Which allows it to be solid

or typically solid at room temperature.

And these are sometimes associated with,

I don't want to get into the whole nutritional battles

about saturated fat and fat's good or bad.

But these are sometimes associated

these are sometimes called your bad fats.

But as we'll see they aren't the worse fats.

The worse fats are actually this one right over here.

But we'll talk about that in a second.

So this is saturated fat because a way to think about it

is it's saturated with as many hydrogens as possible.

Now this one of the right,

and I don't know anything about it

it has all single bonds.

Now over here, or all single bonds between the carbons.

Over here we see a double bond.

We see a double bond between that carbon and that carbon.

And because of that,

this carbon already has three covalent bonds

so it's only gonna be bonded with one hydrogen.

This one already has three covalent bonds

so it's only gonna be bonded with one hydrogen

as opposed to two like these characters over here.

And because of that we don't have

as many hydrogens on the chain as possible.

So we consider this to be an unsaturated fat.

Unsaturated fat.

We don't have as many hydrogens as possible.

And because of that unsaturated fat,

and specially polyunsaturated fats,

these double bonds they tend to form

these kinks in the structure

which keep the molecules from getting really, really dense

which tends to make them liquid or more likely to be liquid

at room temperature.

So this is an unsaturated fat.

This right over here, we have multiple,

we have multiple double bonds in play.

This is called a polyunsaturated fat.

Polyunsaturated fat.

And since this actually only has,

they're both unsaturated fats.

This is a polyunsaturated fat.

And since this only has one double bond

we can call this a monounsaturated fat.

So these are both unsaturated fat.

This is many times happening so poly.

This is happening once, so we call it monounsaturated fat.

Now one question you might have is

why are the kinks forming for

this molecule and this molecule.

And why are they not forming with this molecule

even though this one has double bonds as well.

And this goes to our good friends

cis and trance.

And so you might remember,

if you have a double bond between carbons.

And lets say that you have,

lets say that you have one configuration.

Let me just do it this way.

Lets say you've one configuration where

this is attached to some type of a carbon chain,

and lets say that this is a hydrogen.

Then on the other side the rest of the carbon chain

it could be in one of two configurations.

The rest of the carbon

the rest of the carbon chain could

be on the same side as the carbon chain on the left.

So I'll put R' there.

And, let me do that in the same color.

So you have your hydrogen.

So this is one configuration.

Now another configuration would be

carbon double bonded to carbon.

You have your hydrogen but now the hydrogens

are on opposite sides.

And your chains,

the rest of the carbon chains

are on opposite sides.

And as we talked about before,

this is because double bonds are rigid.

You can't rotate around it.

So it matters, these are actually different,

these are actually different isomers right over here.

Depending on whether this chain is on

the same side as this chain.

Or whether is on the same side.

When it's on the same side

we call this a cis configuration

and this is a trans, trans configuration.

And it turns out that most naturally

produced unsaturated fats are in the cis configuration.

And because they're on the cis configuration

whenever you have these double bonds,

it forms, it makes the chain actually bend.

And if you have many of these double bonds

it makes it bend a lot.

And so polyunsaturated fats are even more

likely to be liquid because it's very hard to pack them.

So what's going on over here?

Well these are actually the configuration

where the, I guess you could say,

the rest of the carbon chains

are on opposite sides of the double bond.

Notice this carbon chain it might be

a little bit hard to see

is above the double bond.

We formed a covalent bond going upward there.

While this carbon chain,

right over here, is below the double bond.

And because of that it doesn't form a kink

and these are in the trans configuration.

And so this right over here,

this is called a trans fat.

This is called a trans fat.

And they aren't typically found,

they aren't typically found in nature.

Now it's interesting about trans fats

is a lot of folks say "hey you know, okay,

"maybe saturated fat is bad for us.

"Maybe we shouldn't eat as much butter and all of that".

And some of that's even up for debate these days.

And they say, "what if we started with unsaturated fats?".

Which are typically viewed as more healthy,

our polyunsaturated fat.

And were just throw a bunch of hydrogens on them,

may be not to fully saturate it,

but enough hydrogen so that some of these

double bonds disappear.

And so it's more solid at room temperature which

might make it a good replacement for butter in cooking.

And a lot of the shortening that you might have seen

even 10, 15 years ago, or even today in a lot of places,

they're essentially trans fat.

And so what happened is is that,

yes, you can replace a lot of these,

you can start to saturate it more with hydrogens.

But that process also turned some of the

cis double bonds

into trans double bonds.

And at first people said, "oh that's harmless,

"this is probably good for you, it's still unsaturated".

But it has some of the properties of a saturated fat.

It's nice and solid and buttery and all of that.

And maybe is even cheaper to produce.

You can take it from other oils.

But it turns out that this is very unhealthy.

There's a lot of debates in nutrition,

but this is unequivocally unhealthy.

This does not exist in nature

and it has all sorts of bad impacts.

And that's why a lot of states, and even countries

have now banned trans fats.

They actually, I've even heard people

go so far and say "this is actually poisonous

"to your body" in certain ways.

And it really affects you in extremely negative ways.

That might be extra strong language

but I'm, I guess I'm trying to scare you a little bit.

Don't eat trans fats.

Anyway, hopefully you enjoyed that.