Intro to Lipids: Study with Video Lessons, Practice Problems & Examples

Lipids, derived from the Greek word "lipo" meaning fat, are diverse hydrocarbon-based biomolecules that are hydrophobic and insoluble in polar water. They can be categorized into hydrolyzable lipids, like triglycerides and phospholipids, which contain fatty acids, and non-hydrolyzable lipids, such as steroids and terpenes. Key functions of lipids include energy storage, insulation, bio-signaling, and forming cell membrane structures, facilitating nutrient transport and ion passage within biological systems.

Intro to Lipids Concept 1

Hey, everyone. So in this video, we're going to take a look at lipids. Now, lipids itself comes from the word "lipo," which is Greek in origin, and it means "fat". Now, when we say lipids, we're going to say that they represent hydrocarbons. So, hydrocarbon-based biomolecules that are hydrophobic, which means they'll be insoluble in polar water, and that's because they themselves are non polar. Here, we're going to say that they are very diverse structurally and functionally, and we'll see how lipids can be broken down into various groups. Lipids can be categorized based on the ability to be hydrolyzed to produce smaller molecules. We're going to say here that many lipids contain what we call fatty acids. A fatty acid is just a long unbranched hydrocarbon chain with a carboxylic acid group at the end. If we take a look here at this graph of the types of lipids, we'd see here in the top left corner, this represents a fatty acid. As you can see, it's just a long hydrocarbon chain with a carboxylic acid at the very end. Here, lipids themselves, we basically break it up into things that are hydrolyzable and things that are not. The two broad categories initially will be hydrolyzable and non hydrolyzable. The non hydrolyzable, although their structures are more complex, there's fewer of them to look at. Here we have our eicosanoids, our steroids, and our terpenes. Then, if we look at our hydrolyzable ones, we have our waxes, which are basically an alcohol ester with a fatty acid connected. We have our Glycerolipids, and here, this one can be broken down into our Triacylglycerols, sometimes called our Triglycerides. Here, it's just a glycerol molecule connected to three fatty acid groups. It then could connect to what's here in this purple box, which also connects it to our sphingolipids. Here, our Glycerolipids and our Sphingolipids, they together help to make our Phospholipids. In it, we have our Phosphoglycerides, so again we have our glycerol molecule here, but instead of being connected to three fatty acids, it's only connected to two with the third portion being a phosphate group connected to an amino alcohol. And then here with our sphingomyelins, instead of having a glycerol, we have here our sphingosine connected to a fatty acid, connected again to a phosphate group with an Amino Alcohol. Again, we can see that these groups are pretty diverse and different from each other. They share some similar characteristics, but there are some key differences between them which we'll go over in terms of many of these molecules when it comes to lipids. Alright. So just keep in mind when we're talking about lipids, fatty acids is just a key part of many of them. Not all of them possess it, but many of them do. And when we're talking about lipids, we can break it down into those that are hydrolyzable and those that are not hydrolyzable.

Intro to Lipids Concept 2

Now remember, we said that lipids can be very diverse structurally and functionally. Here are some primary lipid functions; we have our energy source and storage when it comes to certain types of them. Next, we have insulation and protection. So, this person shivering can be helped by lipids that provide insulation to keep us warm. Next, we have Bio Signaling. We can utilize them to communicate between different biomolecules within a living system. And then finally, we have our cell membrane structure. Some of these diverse forms of lipids form integral parts of different types of cells, in terms of their cell membranes. They help with the transportation of nutrients into the cell and aid in the passage between membranes of ions and different types of helpful components for any biological system. So, these are just some of the main primary functions of a lipid.

Intro to Lipids Example 1

In this example question it asks, which of the following statements about lipids are not true?

Option A: Steroids are a class of lipids which cannot be hydrolyzed by water. Remember when we looked at that graph where we had the two broad groups where lipids are either hydrolyzable or not hydrolyzable, we saw that steroids were indeed in the not hydrolyzable category. So, this statement here is true.

Option B: All lipids are insoluble in non-polar solvents but soluble in polar solvents. Lipids themselves, we said that they are hydrophobic because they are non-polar. Because they're non-polar, they would be soluble in non-polar solvents such as hexanes, but they would be insoluble in solvents like water. Thus, this statement is false, and it is our answer.

Option C: Certain lipids play an important role as components of biological membranes. Yes, when we're talking about our phospholipids, we know that from biology we have a connection between phospholipids and biological membranes, so this is true.

Option D: Lipids contain a large number of non-polar Carbon Hydrogen bonds making them overall non-polar. This is true. Although they possess a polar carboxylic acid end when it comes to fatty acids for those types of lipids, not all lipids have that. Lipids, basically overall, are non-polar because of the large presence of Carbon Hydrogen bonds. So, this statement here is true.

So, out of all our choices, only option B is an incorrect statement and therefore our final answer.

Here’s what students ask on this topic:

What are the main types of lipids and their functions?

Lipids are categorized into hydrolyzable and non-hydrolyzable types. Hydrolyzable lipids include triglycerides, phospholipids, and waxes, which contain fatty acids. Non-hydrolyzable lipids include steroids, terpenes, and eicosanoids. The main functions of lipids are energy storage, insulation and protection, bio-signaling, and forming cell membrane structures. Triglycerides store energy, phospholipids form cell membranes, and steroids like cholesterol are involved in signaling and membrane fluidity. Waxes provide protective coatings, while terpenes and eicosanoids play roles in signaling and metabolic pathways.

How are lipids classified based on their ability to be hydrolyzed?

Lipids are classified into hydrolyzable and non-hydrolyzable categories. Hydrolyzable lipids can be broken down into smaller molecules and include triglycerides, phospholipids, and waxes. These lipids contain fatty acids that can be released through hydrolysis. Non-hydrolyzable lipids, such as steroids, terpenes, and eicosanoids, cannot be broken down into smaller molecules through hydrolysis. These lipids have more complex structures and serve various functions, including signaling and structural roles in cell membranes.

What is the structure of a fatty acid?

A fatty acid is a long, unbranched hydrocarbon chain with a carboxylic acid group at one end. The general structure can be represented as R-COOH, where R is the hydrocarbon chain. The length of the hydrocarbon chain can vary, typically ranging from 4 to 28 carbon atoms. Fatty acids can be saturated, with no double bonds between carbon atoms, or unsaturated, with one or more double bonds. The presence of double bonds affects the physical properties and functions of the fatty acid.

What roles do lipids play in cell membrane structure?

Lipids, particularly phospholipids, play crucial roles in cell membrane structure. Phospholipids form a bilayer, with hydrophobic tails facing inward and hydrophilic heads facing outward, creating a semi-permeable membrane. This bilayer structure allows for the selective transport of nutrients and ions into and out of the cell. Additionally, cholesterol, a type of steroid lipid, is embedded within the membrane, contributing to membrane fluidity and stability. Sphingolipids also play a role in cell signaling and membrane structure.

What are the primary functions of lipids in biological systems?

Lipids serve several primary functions in biological systems. They act as energy storage molecules, with triglycerides storing energy in adipose tissue. Lipids provide insulation and protection, helping to maintain body temperature and protect organs. They are involved in bio-signaling, with molecules like steroids and eicosanoids participating in cellular communication. Additionally, lipids are essential components of cell membranes, forming the lipid bilayer that regulates the passage of substances into and out of cells and maintaining membrane integrity.