Lipids — Overview & Importance in Biology

(Video) Lipids | Fats, Steroids, and Phospholipids

by 2 Minute Classroom

What are lipids, what do they look like, what properties do they have, and what do they do for organisms? This video offers a quick look into the answers to these questions.

What Are Lipids?

Lipids are a group of macromolecules that have a lot of functions, including storing energy, signaling between cells, and forming the cell membrane. They are made from monomers called fatty acids.

Lipids are not soluble in water, making them especially important in cell function. Unlike water, these molecules are non-polar, which means they won't mix with water.

In fact, lipids are referred to as hydrophobic, which literally means "water-fearing." If you have ever tried to mix oil and water, you've probably noticed that they remain separate. This is because oil is a lipid and non-polar.

Saturated or Unsaturated?

You've probably heard of saturated and unsaturated fats on TV ads, nutrition labels, and billboards. The difference between them, structurally, is actually really small. Let's take a look:

Saturated fats have straight chains because the chain part of their structure has only single carbon-carbon bonds. Saturated fats pack together closely and are solid at room temperature. Saturated fats are typically found in animal products. Butter is a good example (from an animal, solid at room temp).

Unsaturated fats have a kink in their chain, caused by double or triple carbon-carbon bonds in the chain part of their structure. Because of these kinks, unsaturated fats can't pack together very closely, making them liquid at room temperature. They are typically found in plant products. Vegetable oil is a good example (from a plant, liquid at room temp).

Triglycerides

Lipids that store energy are called triglycerides. In many organisms, extra carbohydrates are often stored as triglycerides in fat tissue.

Triglycerides are excellent long-term energy storage molecules because they will not mix with water and degrade. We can also eat triglycerides (in delicious fried foods, often) and break them down to get energy.

Phospholipids

Phospholipids are a type of lipid that form cell membranes. They have two parts: the hydrophilic head (attracted to water) and the hydrophobic tail (repelled by water).

Two different layers of phospholipids form cell membranes. Because of this, cell membranes are also called phospholipid bilayers (bi means "two").

Steroids and Waxes

Steroids and waxes are the last group.

Steroids are often found in the cell membrane, supporting its structure. The most common membrane steroid is cholesterol. Because the interior of the cell membrane is hydrophobic, things that go through it also have to be
hydrophobic.

This is why extra cholesterol can be so dangerous; it doesn't dissolve in water so if there is a build up in the bloodstream it won't dissolve away. But, don't forget that normal amounts of cholesterol are absolutely necessary to keep you alive and to keep your cell membranes nice and fluid. It's all about having a good balance of the right amount and type of cholesterol.

Steroids can also be used as signaling molecules. Hormones like estrogen and testosterone are released by some cells and received by others as signals to change and develop.

Finally, waxes are manufactured by organisms as a protective barrier against water and other contaminants.

Types of Lipids

Lipids include fats, oils, waxes, and steroids. They are insoluble in water, which allows our bodies to use them as waterproof barriers and as components of cell membranes. They are also used to store energy, similar to polysaccharides.

Lipids contain more $C-H$ bonds than carbohydrates and fewer oxygen atoms. The long hydrocarbon chain is nonpolar, while the small part with the oxygen is polar. This means that they are mostly nonpolar, so they are not soluble in water. Instead, lipids are soluble in fat and oils.

Saturated fatty acids occur when each carbon atom in the chain is linked by a single bond. The name saturated comes from the fact that each carbon atom has the maximum possible amount of hydrogens attached to it. They are typically solid at room temperature.

Unsaturated fatty acids have one carbon-carbon double bond. Polyunsaturated fatty acids happen when the chain has more than one carbon-carbon double bond. These types of lipids are typically liquid at room temperature, like olive oil.

Most lipids are made up of a glycerol molecule combined with three fatty acids, called a triglyceride. If the lipid has a phosphate group attached to two fatty acid chains, it is called a phospholipid.

Steroids are the last type of lipid. They are used for chemical signals such as some hormones and vitamins.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Monomer}}$ : Any molecule that can react with other molecules of the same or different makeup to form a chain, or polymer

$\color{#8925AE}{\text{Polymer}}$ : A chain of monomers made of a specific type of compound

$\color{#8925AE}{\text{Macromolecule}}$ : A polymer that has a large (macro) molecular mass. There are four main types in organisms: carbohydrates, proteins, lipids, and nucleic acids

$\color{#8925AE}{\text{Saturated}}$ : Saturated fatty acids occur when each carbon atom in the chain is linked by a single bond

$\color{#8925AE}{\text{Unsaturated}}$ : Unsaturated fatty acids have one carbon-carbon double bond

$\color{#8925AE}{\text{Lipid}}$ : Fats and oils. Made up of a glycerol molecule and three fatty acid chains

Saturated and Unsaturated Fats

Lipids are the main macromolecule in our body that is used for energy storage, hormones and steroids, and cell structures and membranes. They are a major component of living cells. Lipids are made up of their monomers glycerols, fatty acids, and steroids, which make a few different polymers. The terms monomer and polymer can be confusing, so just think of monomers as one bead and then polymers as the bracelet. One of the most used examples of lipids is fats. Fats are typically made up of glycerol and fatty acids.

A common type of fat is called a triglyceride which is made of a glycerol and three fatty acids (carboxylic acids). These fats can either be saturated or unsaturated depending on the bonds within the fat. If a fat has no double bonds, it is considered to be saturated with hydrogen. If a fat has a double bond, it is considered to not be saturated with hydrogen and is called unsaturated.

Lipids also form steroids. Steroids are made of four carbon rings bonded together with different functional groups. Cholesterol is an example of a prominent steroid in our bodies.

Another extremely important lipid is the phospholipid. These molecules consist of a phosphate group, a glycerol, and two fatty acid chains. With these different components, phospholipids take on a unique structure. Since the phosphate group is polar, phospholipids have a polar head that is attracted to water and is hydrophilic. The two fatty acid chains cause there to be a hydrophobic tail. Phospholipids are common in our bodies and make up cell membranes. This is often called a "bilayer" where the hydrophilic heads face outwards while the hydrophobic tails hide on the inside.

Lipids are abundant in our diets in the form of fats. In fact, it's important to eat a variety of them including fatty acids and triglycerides. Fats get a bad rap, but they're critical for cell function.

(Video) Biomolecules

by Amoeba Sisters

There are four major biomolecules, including lipids, that make up life as we know it. In this video, the Amoeba Sisters go through the structures of lipids and the other biomolecules, as well as the actions of the different biomolecules.