Introduction to lipids | High school biology | Khan Academy

Summary

In this educational video, the instructor delves into the world of lipids, explaining that while fats are a subset of lipids, not all lipids are fats. Lipids are a class of molecules with varying solubility in water, possessing both hydrophobic and hydrophilic parts. They play crucial roles in energy storage, cell signaling through hormones, and are integral to the structure of cellular membranes. The video also touches on the molecular structure of fats, including triglycerides, and the concepts of saturated and unsaturated fats. The instructor emphasizes the importance of fats for health and the diverse roles lipids play in biological systems.

Takeaways

• 🔬 Lipids are a class of molecules that are not very water-soluble and play various roles in biological systems.
• 🍗 Fats are a type of lipid, but not all lipids are fats; lipids can have both hydrophobic and hydrophilic parts.
• 🏋️‍♂️ Lipids are crucial for energy storage in the body, as seen with body fat acting as an energy reserve.
• 📣 Lipids, particularly hormones, are involved in signaling processes within the body.
• 🛡️ Lipids, such as phospholipids, are essential components of cellular membranes due to their amphiphilic nature.
• 🧬 The structure of a fat molecule typically consists of three fatty acids attached to a glycerol backbone, forming a triglyceride.
• 💧 The hydrocarbon chains in fats make them hydrophobic and less soluble in water, which is why fats don't mix well with water.
• 🔗 Saturated fats have all available bonding sites filled with hydrogen, while unsaturated fats have double bonds, leaving room for more hydrogens.
• 🌱 Essential vitamins, which are lipids, require fat for proper absorption into the body.
• 🧠 Other lipids, like sphingomyelin, are important for the myelin sheath in the brain and contribute to the structure of cellular membranes.

Q & A

What is the primary association of lipids?

Lipids are often associated with fats, but not all lipids are fats. They are a class of molecules that are not very soluble in water.

What are the two main types of lipids in terms of their interaction with water?

Lipids have hydrophobic parts that are not attracted to water and hydrophilic parts that are attracted to water.

What are some of the roles lipids play in the body?

Lipids play roles in energy storage, signaling through hormones, and are involved in the formation of cellular membranes.

What is the structure of a fat molecule?

A fat molecule typically consists of three fatty acids connected to a glycerol, forming a triglyceride.

Why are triglycerides not very soluble in water?

Triglycerides are not very soluble in water because of their long hydrocarbon chains, which lack polar molecules or charges that would allow them to dissolve in water.

What is the difference between saturated and unsaturated fats?

Saturated fats have their carbons bonded to as many hydrogens as possible, while unsaturated fats have double bonds in their hydrocarbon chains, allowing for more hydrogen bonding.

Why are fats essential for life?

Fats are essential because they help in the absorption of fat-soluble vitamins and are necessary for various bodily functions.

What is sphingomyelin and what is its role in the body?

Sphingomyelin is a type of lipid involved in the formation of the myelin sheath in the brain, which helps electrically insulate neurons, and it is also a substantial part of the phospholipids in cellular membranes.

How do phospholipids contribute to the structure of cellular membranes?

Phospholipids have a hydrophilic head that is attracted to water and a hydrophobic tail that repels water, allowing them to form bilayers that are the basis of cellular membranes.

What does the cross-section of a cellular membrane look like?

The cross-section of a cellular membrane looks like two layers of phospholipids with their hydrophilic heads facing the water on both sides and their hydrophobic tails facing away from the water in the middle.

Why are lipids considered macromolecules?

Lipids are considered macromolecules because they can be composed of many atoms, making them large and complex molecules.

Outlines

00:00

🧬 Lipids: More Than Just Fats

The video segment introduces lipids, emphasizing that while fats are a type of lipid, not all lipids are fats. Lipids are described as a class of molecules found in biological systems that are not very soluble in water. They can have both hydrophobic and hydrophilic parts, which is significant for their roles in the body. These roles include energy storage, signaling through hormones (many of which are lipids), and forming cellular membranes. The structure of a fat molecule, specifically a triglyceride, is explained, highlighting the three fatty acids attached to a glycerol. The concept of saturated and unsaturated fats is introduced, relating to the bonding of hydrogen atoms on the hydrocarbon chains. The necessity of fats for life is underscored, as they aid in the absorption of fat-soluble vitamins. The video also briefly mentions other types of lipids and their structures, noting their hydrophobic and hydrophilic properties and their importance in membrane formation.

05:00

🧠 Cellular Membranes and Lipid Structure

This part of the script delves into the structure of cellular membranes, which are composed of lipids, particularly phospholipids. It describes how phospholipids have a hydrophilic head that is attracted to water and a hydrophobic tail that repels water, allowing them to form the bilayer structure of cell membranes. The video uses a visual analogy of circular heads and tail chains to illustrate this arrangement. The importance of lipids in the formation of the myelin sheath in the brain is highlighted, which is crucial for the electrical insulation of neurons. The segment concludes with a mention of lipids, carbohydrates, proteins, and nucleic acids as the major macromolecules in biological systems, noting their large size and complex composition.

Keywords

💡Lipids

Lipids are a broad class of organic molecules that include fats, oils, waxes, and other related compounds. They are characterized by being insoluble in water, which means they do not mix well with water. In the video, lipids are discussed as essential components of biological systems, playing roles in energy storage, cell signaling, and the formation of cell membranes. An example from the script refers to lipids having both hydrophobic (water-repelling) and hydrophilic (water-attracting) parts, which is crucial for their function in biological membranes.

💡Fats

Fats are a type of lipid that is primarily used for energy storage in the body. They are composed of glycerol and fatty acids. The video script mentions that fats are lipids, but not all lipids are fats, highlighting the broader category that lipids represent. An example given is the concept of triglycerides, which are fats made up of three fatty acids attached to a glycerol molecule.

💡Hydrophobic

Hydrophobicity refers to the property of certain molecules to repel water. In the context of the video, lipids have hydrophobic parts, which are their long hydrocarbon chains. These parts do not dissolve well in water due to the lack of polar bonds that would typically attract water molecules. The script explains that these hydrophobic regions of lipids help them avoid water, which is important for their structure in biological systems.

💡Hydrophilic

Hydrophilic molecules have an affinity for water and can dissolve in it. The video discusses how some lipids have hydrophilic parts that are attracted to water. This dual nature of lipids, having both hydrophobic and hydrophilic regions, is essential for their role in forming cellular membranes, as highlighted in the script when discussing the structure of phospholipids.

💡Energy Storage

Energy storage in the context of the video refers to the role of fats as a means of storing energy within organisms. Fat molecules can be broken down to release energy when needed. The instructor humorously refers to the energy stored in body fat, suggesting that it's there to protect the abdominal muscles, illustrating the concept in a relatable way.

💡Signaling

Signaling in biology refers to the process by which cells communicate with each other. The video mentions that lipids, particularly hormones, are involved in signaling. Hormones, which are lipids, transmit signals from one part of the body to another, playing a crucial role in regulating various bodily functions.

💡Membrane

A membrane, as discussed in the video, is a barrier that separates the interior of a cell from the external environment. Lipids, specifically phospholipids, are key components of cellular membranes. The script explains that the dual nature of phospholipids, with one end being hydrophobic and the other hydrophilic, allows them to form the bilayer structure of cell membranes.

💡Phospholipids

Phospholipids are a type of lipid that contains a phosphate group. They are a major component of all cell membranes. The video script describes phospholipids as having a hydrophilic head and a hydrophobic tail, which allows them to spontaneously arrange into bilayers with the hydrophilic heads facing the watery environments inside and outside the cell, and the hydrophobic tails facing each other, away from the water.

💡Triglycerides

Triglycerides are a type of lipid consisting of a glycerol molecule attached to three fatty acid chains. The video script uses the term 'triglyceride' to explain the structure of fats, where 'tri-' refers to the three fatty acids, and '-glyceride' refers to the glycerol backbone. Triglycerides are储能形式，且在视频中提到它们在水中不溶性是由于其长的烃链。

💡Saturated Fat

Saturated fat refers to fats in which the hydrocarbon chains of the fatty acids are fully saturated with hydrogen atoms, meaning there are no double bonds between the carbon atoms. The video script contrasts saturated fats with unsaturated fats, which have double bonds in their hydrocarbon chains and can thus incorporate more hydrogens. Saturated fats are typically solid at room temperature and are found in many animal products.

💡Unsaturated Fat

Unsaturated fat contains one or more double bonds in the hydrocarbon chains of its fatty acid components, which means they have fewer hydrogen atoms and are typically liquid at room temperature. The video script mentions that unsaturated fats could potentially bond to more hydrogens due to the presence of these double bonds, contrasting their structure with that of saturated fats.

Highlights

Lipids are often associated with fats, but not all lipids are fats.

Lipids are a class of molecules that are not very water-soluble.

Lipids can have both hydrophobic and hydrophilic parts.

Fat molecules play a role in energy storage in the body.

Lipids are involved in signaling as many hormones are lipids.

Phospholipids are crucial in forming cellular membranes.

Phospholipids have one end that repels water and another that attracts water.

Fat molecules are composed of three fatty acids connected to a glycerol.

Triglyceride is another term for fat, derived from three fatty acids and glycerol.

Hydrocarbon chains in fats make them insoluble in water.

Saturated fats have carbons fully bonded with hydrogens, while unsaturated fats have double bonds.

Fats are essential for life as they aid in the absorption of fat-soluble vitamins.

Sphingomyelin is a lipid involved in the myelin sheath of the brain and is also a component of cell membranes.

The hydrophilic part of sphingomyelin helps in forming membrane structures.

Cellular membranes have a cross-sectional view with hydrophilic heads facing water and hydrophobic tails facing away.

Lipids, along with carbohydrates, proteins, and nucleic acids, are major macromolecules in biological systems.

Macromolecules are composed of many atoms, distinguishing them from small molecules.

Transcripts

- [Instructor] What we are going to do in this video

is talk a little bit about lipids.

Now, a lot of times,

lipids are strongly associated with fats,

and that's not incorrect.

Fats are lipids,

but not all lipids are fats.

A better definition or a better association

for lipids would be a class of molecules

that you often see in biological systems that are not so

water

soluble.

And I didn't say outright hydrophobic,

which means not attracted to water,

because there are definitely lipids

that have parts that are hydrophobic,

that are trying to get away from the water.

But there is other parts that are hydrophilic,

that like the water,

that would be attracted to water molecules.

Now, in terms of roles they play in the body,

and we can think of fat molecules here,

well, they definitely play a role

in terms of energy

storage.

Whenever I look at my belly,

I just like to think of all that energy

that is there covering my six-pack.

They could be involved in signaling.

In future videos, we're going to study hormones,

and hormones are nothing but molecules

that help transmit a signal from one part of the body

to another part of the body.

And many of these hormones are lipids.

They're also involved in membranes.

So a lot of the time in biology,

we're gonna talk about cellular membranes

and how they're formed with these phospholipids.

And we'll see these phospholipids, in particular,

have one end that's trying to get away from the water

and another end that is attracted to the water.

And that's actually what makes them good for membranes.

Just going back to fats, let's actually take a look

at what some of these lipid molecules look like.

So this right over here is an example of a fat molecule,

but the general structure you're going to have is

these three fatty acids.

So that's one right over there,

one fatty acid,

two fatty acids,

and three fatty acids

that are connected to a glycerol.

And don't worry too much about the words here.

You'll study them more when you get

to an organic chemistry class.

But that's where this word triglyceride comes from,

tri- for your three fatty acids

and -glyceride from a glycerol.

And triglyceride is, in fact, another word for fat.

And what makes a triglyceride not so soluble in water?

Look at these long hydrocarbon chains where you just

essentially have a bunch of carbons and hydrogens.

Those parts, remember, things that are soluble in water,

they tend to be polar molecules,

things that have a partial charge on one end or another

or even a full charge.

But when we look at these hydrocarbon chains,

they tend to not have these partial charges on

one side or another,

and so that doesn't make them so soluble in water.

And another word that you sometimes hear

associated with fats, saturated or unsaturated fat.

That's really referring to what's going on

on these hydrocarbon chains.

If the carbons are as bonded

to as many hydrogens as they can,

well, then you're talking about a saturated fat.

It's saturated with hydrogens.

If it's not bounded, if it, in theory, it could bond

to more hydrogens because it has some double bonds in there,

well, then it's unsaturated.

Maybe in a future video, we'll talk about the health issues

of saturated versus unsaturated fat.

Sometimes in popular culture, fat gets a bad name

because everyone's trying to get their six-packs

or whatever else, but it's very important to realize that

without fats you would die.

Many vitamins, which are not so soluble in water,

making them, in fact, lipids,

need fat in order to be absorbed into the body properly.

But as I also mentioned, all lipids are not fats.

Here are more examples of lipids,

and I'm not gonna go into detail

into their molecular structure.

But you see something similar here.

They all have long chains of hydrocarbons

that aren't so soluble in water.

These parts right over here would be hydrophobic,

hydrophobic.

But what's interesting, especially about this sphingomyelin,

which is involved in your myelin sheath in the brain,

it helps electrically insulate neurons,

it's also involved in membranes,

it makes up a substantial part

of the phospholipids in membranes,

is that this sphingomyelin right over here

has a part that actually is hydrophilic.

And as we'll see later on,

that's what makes things, molecules like this,

phospholipids, this is a sphingophospholipid,

makes them good for membrane structures.

Because the part that's attracted to the water

could be on the outside,

and the part that's not attracted to the water

could be on the inside.

And so you can form these membranes

that a cross-section of which would look something like this

where the circular parts are the part that want,

the parts that want to be around the water,

while these tails right over here,

these are the hydrophobic chains

that want to go away from the water.

And this is, in fact,

what cellular membranes actually look like

if you were zoom really, really, really far in.

I'll leave you there.

Between lipids, carbohydrates, proteins, nucleic acids,

we've really covered the major macromolecules

that you will see in biological systems.

Once again, what makes them macromolecules?

Well, they can be composed

of many, many, many, many, many atoms.

They aren't small molecules.