Question

Draw the structure of the glycerophospholipid that contains a stearic acid acyl group, an oleic acid acyl group, and a phosphate bonded to ethanolamine.

Short answer

A glycerophospholipid with stearic acid, oleic acid, and ethanolamine attached to phosphate is drawn by assembling these components on a glycerol backbone.

Step-by-step solution

Understanding the Components

To draw the glycerophospholipid, we need to understand its components: a glycerol backbone, two fatty acids (stearic and oleic acids), and a phosphate group bonded to ethanolamine. Glycerophospholipids are built from these components.

Building the Glycerol Backbone

Start with the three carbon chain of glycerol. Label the three carbons as 1, 2, and 3. The fatty acids and phosphate group will attach to these carbons.

Attaching Stearic Acid

Stearic acid is a saturated fatty acid with a 18-carbon chain. Attach it to the first carbon (C-1) of the glycerol backbone through an ester bond.

Attaching Oleic Acid

Oleic acid is a monounsaturated fatty acid with a double bond located at the 9th carbon in its 18-carbon chain. Attach it to the second carbon (C-2) of the glycerol backbone through an ester bond.

Adding the Phosphate Group

Attach a phosphate group to the third carbon (C-3) of the glycerol. This step involves creating a phosphodiester bond between the glycerol and the phosphate group.

Bonding Ethanolamine to Phosphate

Connect ethanolamine to the phosphate group, completing the structure of the glycerophospholipid. Ethanolamine attaches via the phosphatidylethanolamine bond.

Reviewing the Complete Structure

Once all components are connected, review the structure to ensure that stearic acid is on C-1, oleic acid is on C-2, and the phosphate on C-3 is bonded to ethanolamine.

Key concepts

Glycerol Backbone

The glycerol backbone is the central framework of glycerophospholipids. It consists of a simple three-carbon chain. Understanding this backbone is essential because it serves as the foundation to which other molecules attach.
Each carbon in the glycerol molecule is numbered from 1 to 3. This helps in identifying where different components, like fatty acids and phosphate groups, will be attached.
The glycerol backbone provides stability and structure, making it an integral part of lipid molecules. This backbone is hydrophilic, meaning it can interact with water, which is crucial for the function and formation of cellular membranes and lipid bilayers.

Fatty Acids

Fatty acids are long hydrocarbon chains that can be either saturated or unsaturated. In glycerophospholipids, two fatty acids are attached to the glycerol backbone. Let’s break this down.

• Saturated Fatty Acid: An example is stearic acid. It has no double bonds, meaning it has a straight chain, which makes it pack closely with other molecules.
• Unsaturated Fatty Acid: An example is oleic acid. It has a double bond that introduces a kink in the chain, affecting how it packs.
  

Fatty acids attach to the glycerol backbone through ester bonds. Saturated fatty acids often increase the melting point, leading to more solid structures, while unsaturated fatty acids promote fluidity in membranes.

Phosphate Bond

A phosphate bond is a critical component in the structure of glycerophospholipids. The phosphate group is attached to the third carbon of the glycerol backbone. This attachment is what defines phospholipids.
Phosphates are negatively charged, which makes them hydrophilic. This hydrophilicity is crucial because it allows phospholipids to form the bilayer structure of cell membranes, orienting themselves so that the hydrophobic fatty acid tails are shielded from water.
The phosphate group serves as a bridge. It not only attaches to glycerol but also connects to other molecules, like ethanolamine, via phosphodiester bonds. This attachment facilitates the formation of diverse lipids with various functional roles in cells.

Ethanolamine

Ethanolamine is a simple molecule that is connected to the phosphate group in some glycerophospholipids. This forms a class of phospholipids called phosphatidylethanolamine.
Ethanolamine contributes to the cell membrane’s flexibility and function. It adds a polar head group to the lipid, enhancing its interaction with aqueous environments.
This molecule is important in cellular processes like membrane fusion and cell signaling. By being attached through a phosphodiester bond to the phosphate, ethanolamine aids in stabilizing structures within cells. It plays a role in maintaining membrane integrity and facilitating cell dynamics.

Ester Bond

Ester bonds are essential connections in glycerophospholipids, linking the fatty acids to the glycerol backbone. This bond is formed by a reaction between an alcohol and a carboxylic acid, resulting in this crucial connecting link.
In the context of glycerophospholipids:

• Each glycerol carbon may form an ester bond with a fatty acid.
• Ester bonds result in the release of water in a process known as condensation.

These bonds are significant because they provide the structure with flexibility and stability. Ester bonds are generally considered quite stable, yet they can be broken down by hydrolysis, a reaction that is important in lipid metabolism and remodeling.

Phosphodiester Bond

Phosphodiester bonds are vital links in the structure of glycerophospholipids, connecting the phosphate group to other molecules, such as ethanolamine.
This bond forms between the hydroxyl group of a phosphate and an alcohol group of ethanolamine. This kind of bond is versatile and robust, often contributing to stability.
In biological systems, phosphodiester bonds are essential for linking nucleotides in DNA and RNA. In lipids, these bonds allow for the formation of phosphatidylethanolamine. They are crucial for membrane dynamics, impacting how molecules interact within and across the lipid bilayer.