Name: lipids in cells: fats and membranes
Uploaded: 2020-11-23T11:47:33.000Z
Duration: 2 min 5 s
Channel: JoVE

Lipids are biomolecules grouped by a shared property. They are hydrophobic, meaning they do not dissolve in water.This is because they are mainly made of nonpolar hydrocarbon chains that lack charge and cannot form hydrogen bonds with water.Based on their structure and components, lipids are divided into three classes: fats, phospholipids, and steroids.Fats, also called triglycerides, are made up of a glycerol molecule and three fatty acids.They are classified as saturated or unsaturated based on whether their fatty acids have double bonds. Saturated fatty acids have no double bonds in their hydrocarbon chain and carry the maximum number of hydrogen atoms, while unsaturated fatty acids have one or more double bonds.These saturated and unsaturated fatty acids are also present in phospholipids. However, only two fatty acids are attached to the glycerol, and a charged phosphate group replaces the third fatty acid.This gives phospholipids a unique feature: a hydrophilic phosphate head and hydrophobic hydrocarbon tails. These molecules form a bilayer that makes up the cell membrane.The hydrophilic phosphate heads are in contact with the aqueous solution inside and outside the cell, whil

what are lipids?

What are Lipids?

Lipids are a group of structurally and functionally diverse organic compounds that are insoluble in water. Certain classes of lipids, such as fats, phospholipids, and steroids are crucial to all living organisms. They function as structural components of cellular membranes, energy reservoirs, and signaling molecules.Lipids are a Diverse Group of Hydrophobic Molecules Lipids are a structurally and functionally diverse group of hydrocarbons. Hydrocarbons are chemical compounds that consist of carbon and hydrogen atoms. The carbon-carbon and carbon-hydrogen bonds are nonpolar, which means that the electrons between the atoms are shared equally. The individual nonpolar bonds impart an overall nonpolar characteristic to the hydrocarbon compound. Additionally, nonpolar compounds are hydrophobic, or &#x201C;water-hating.&#x201D; This means they do not form hydrogen bonds with water molecules, rendering them nearly insoluble in water.Depending on the chemical composition, lipids can be divided into different classes. The biologically important classes of lipids are fats, phospholipids, and steroids.Fat Is a Triester of Fatty Acids and Glycerol The hydrocarbon backbone of fat has three carbon atoms. Each carbon carries a hydroxyl (&#x2013;OH) group, making it glycerol. To form a fat, each of the hydroxyl groups of glycerol is linked to a fatty acid. A fatty acid is a long hydrocarbon chain with a carboxyl group (&#x2013;COOH) at one end. The carboxyl group of the fatty acid and the hydroxyl group of the glycerol form a stable bond with the release of a water molecule. The resulting molecule is called an ester (&#x2013;COOR). Fat is an ester of glycerol and three fatty acids; hence it is also referred to as triglyceride. The three constituent fatty acids can be identical or different and are usually 12-18 carbons long.Saturated Versus Unsaturated Fats Fats are either saturated or unsaturated depending on the presence or absence of double bonds in the hydrocarbon chains of their fatty acids. If a fatty acid chain does not have double bonds between the carbon atoms, the individual carbon atoms bind a maximum number of hydrogens. Such a fatty acid is completely saturated with hydrogen, and is called a saturated fatty acid. On the other hand, if the fatty acid contains one or more double bonded carbon atoms, the fatty acid is called unsaturated fatty acid.Fats that contain all saturated fatty acids are called saturated fats. Fats obtained from animal sources, for instance, butter, milk, cheese, and lard, are mostly saturated. Fats from fish or plant sources are often unsaturated, like olive oil, peanut oil, and cod liver oil. The absence of double bonds in the hydrocarbon chains of saturated fatty acids, makes them flexible. The flexible fatty acid chains can pack tightly with each other; hence saturated fats are mostly solid at room temperature.Most naturally occurring unsaturated fatty acids are in &#x201C;cis&#x201D; conformation, meaning that the hydrogen atoms adjacent to the carbon-carbon double bond are on the same side. The presence of cis-double bonds causes a bend in the hydrocarbon chain which makes the long hydrocarbon chain less flexible and difficult to pack. As a consequence, most unsaturated fatty acids are liquid at room temperature.Fats are a long-term energy reservoir in many organisms. If the need arises, the organism breaks down fats to produce energy. In animals, fat provides cushioning around vital organs, and a subcutaneous layer of fat insulates the body from external temperatures.Phospholipids Are an Integral Part of Cellular Membranes Phospholipids are critical to the cell as they are major constituents of cell membranes. Phospholipids are structurally similar to fats but contain only two fatty acids linked to glycerol instead of three. The fatty acid residues can be saturated or unsaturated. In phospholipids, the third hydroxyl group of glycerol is linked to a negatively charged phosphate group.An additional functional group attached to the phosphate group can lead to diverse chemical properties of phospholipids. Most common additives are small polar groups like choline or serine.Phospholipids are amphipathic molecules, meaning they have parts that are hydrophobic and others that are hydrophilic, or water-loving. When phospholipids are added to water, they spontaneously form a bilayer, a thin film that is two phospholipid molecules thick. This self-organization takes place because the polar heads are attracted to water, while the hydrophobic fatty acids are buried in the center of the layer to evade contact with water. Such phospholipid bilayer forms the cell membrane in all living organisms. It compartmentalizes the fluids on the interior and exterior of the cell. Embedded in the bilayer are proteins and steroids, another class of lipids. Additional phospholipid bilayers may further compartmentalize the interior of the eukaryotic cell, for instance, the lysosome and endoplasmic reticulum.Steroids Consist of a Four Ring Structure Steroids are another biologically important class of lipids. Steroids are composed of four carbon rings that are fused to each other. Steroids vary amongst each other based on the chemical groups attached to the carbon rings. Although steroids are structurally different, they are hydrophobic and insoluble in water. Steroids reduce the fluidity of the cell membrane. They also function as signaling molecules within the cell. Cholesterol is the most common steroid and is synthesized by the liver. It is present in the cell membrane and is a precursor of sex hormones in animals.

Overview

Lipids are a group of structurally and functionally diverse organic compounds that are insoluble in water. Certain classes of lipids, such as ...

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Molecular Biology

Unit 1

Biochemistry of the Cell

KEY TERMS AND CONCEPTS

lipids in cells: fats and membranes

Lipids are a group of biomolecules found in living things. They are known for their role in energy storage and in building cell membranes. This makes them important in many parts of biology.

Fats are one common type of lipid. Other lipids include phospholipids and steroids. Each group has a different structure and a different job in the body.

Phospholipids are especially important because they help form cell membranes. Steroids also belong to the lipid group, and they have their own distinct structure. Together, these examples show how lipids support both cell structure and cell function.

Lipids in Cells: Fats and Membranes

the periodic table and organismal elements

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Functional Groups in Organic Molecules

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Lipids are a group of biomolecules found in living things. They are known for their role in energy storage and in building cell membranes. This makes them important in many parts of biology. Fats are one common type of lipid. Other lipids include phospholipids and steroids. Each group has a different structure and a different job in the body. Phospholipids are especially important because they help form cell membranes. Steroids also belong to the lipid group, and they have their own distinct...

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Types of Lipids and Their Structure

Lipids are a major group of biological molecules, and their structure helps explain their different forms. Many lipids are built from fatty acids, which are long hydrocarbon chains with a carboxyl group. The carbon chain is hydrophobic, meaning it does not mix well with water, while the carboxyl group is the acidic end. Triglycerides are one common lipid type. They consist of a glycerol molecule joined to three fatty acid chains. Saturated triglycerides have fatty acids with only single...

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Forces between molecules help explain why matter behaves the way it does. These intermolecular attractions act between separate molecules, not within a single molecule. They are often much weaker than the bonds that hold atoms together inside a molecule, but they still affect many properties of liquids and solids. Several common types of intermolecular forces are covered in this topic. These include dipole-dipole forces, hydrogen bonding, ion-dipole forces, and van der Waals forces. Van der...

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key terms and concepts

Explore lipids as biomolecules used for energy storage and cell membranes. Learn the main lipid groups, including fats, phospholipids, and steroids.

Lipids in Cells: Fats and Membranes | JoVE K12

molecular biology

JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

Lipids in Cells: Fats and Membranes

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