Question

Cardiolipins are a group of lipids found in heart muscles. What products would be formed if all ester bonds, including phosphates, were saponified by treatment with aqueous \(\mathrm{NaOH}\) ?

Short answer

Glycerol, fatty acid salts, and inorganic phosphate are formed.

Step-by-step solution

Understanding Saponification

Saponification refers to the hydrolysis of ester bonds in the presence of an alkali, like \(\mathrm{NaOH}\). In this reaction, esters are converted into alcohol and salt of a fatty acid (soap). Regarding cardiolipins, they have ester bonds between fatty acids and glycerol and a phosphate group.

Identifying the Saponification Products

When the ester bonds in cardiolipins undergo saponification, each yields glycerol and fatty acid salts. Also, saponification of phosphate esters will free the phosphate group as inorganic phosphate.

Determining the Components

Since cardiolipins are diphosphatidylglycerol with two phosphatidic acids bound to a glycerol, treatment with \(\mathrm{NaOH}\) yields multiple glycerols, fatty acid salts, and the inorganic phosphate groups.

Final Products

Thus, the final products of saponifying all ester bonds of cardiolipins are glycerol, salts of fatty acids, and inorganic phosphate.

Key concepts

Lipids

Lipids are a broad group of naturally occurring molecules that include fats, oils, and certain vitamins, among others. They are crucial components of living cells and serve numerous biological functions. Lipids serve as structural components of cell membranes, energy storage molecules, and signaling molecules. Lipids are generally hydrophobic, meaning they do not mix well with water, which makes them excellent barriers in the cell membrane. This characteristic is due to their long hydrocarbon chains.

• Cell membranes: Lipids form the bilayer in cell membranes, providing structure and protection.
• Energy storage: Lipids store energy efficiently, as they yield more energy per gram than carbohydrates or proteins.
• Signaling: Some lipids play a role in signaling pathways, affecting cellular processes.

Understanding lipids is essential when studying how they interact with enzymes, like those involved in the process of saponification.

Ester Bonds

Ester bonds are a type of chemical bond that forms between a carboxylic acid and an alcohol, resulting in the release of a molecule of water. These bonds are prevalent in many biological molecules, including lipids. During the formation of ester bonds, the hydroxyl group ( OH ) from the acid reacts with the hydrogen from the alcohol, creating an ester linkage.

• Structure: Consists of the ester functional group ( R-COO-R' ).
• Biological relevance: Found in fats and oils, which are crucial energy sources for organisms.

In saponification, ester bonds are broken down, leading to the formation of an alcohol (like glycerol) and the sodium salt of a fatty acid.

Phosphate Group

The phosphate group is an essential component of many biological molecules, such as DNA, RNA, and ATP. It consists of one phosphorus atom bonded to four oxygen atoms, creating a tetrahedral shape. In lipids, the phosphate group plays a crucial role in forming phospholipids, which are key in comprising cell membranes.

• Chemical formula: The phosphate group is typically represented as ( PO_4^{3-} ).
• Role in phospholipids: It provides a polar head that allows lipids to interact with water, forming bilayers.

When saponifying cardiolipins, the phosphate group's ester bonds break down, releasing inorganic phosphate into the solution.

Fatty Acids

Fatty acids are long hydrocarbon chains with a carboxylic acid group at one end. They are fundamental components in various lipids, such as triglycerides and phospholipids. Fatty acids can be saturated or unsaturated, depending on the presence of double bonds between carbon atoms.

• Saturated fatty acids: Have no double bonds between the carbon atoms, typically solid at room temperature.
• Unsaturated fatty acids: Contain one or more double bonds, usually liquid at room temperature due to kinks in the chain.

During saponification of cardiolipins, the ester bond between fatty acids and glycerol is hydrolyzed, resulting in free fatty acids or their salts.

Glycerol

Glycerol is a simple polyol compound that serves as the backbone for triglycerides and phospholipids. It consists of three carbon atoms, each having a hydroxyl group ( OH ). Glycerol is sweet-tasting and non-toxic, which is why it has a variety of applications in the food and pharmaceutical industries.

• Structure: ( C_3H_8O_3 ), with each carbon bonded to a hydroxyl group.
• Importance: Acts as the structural backbone for many lipids.

In saponification, glycerol is released when the ester bonds are broken, illustrating its role as a central component in lipid structures.

Inorganic Phosphate

Inorganic phosphate is a byproduct released during the hydrolysis of phosphate esters, such as in ATP or phospholipids. Unlike the bound phosphate groups found in organic compounds, inorganic phosphate exists freely in solution or as salts. It plays essential roles in energy transfer, enzyme regulation, and as a buffer system in biological organisms.

• Association: Commonly involved in cellular energy cycles (e.g., ATP to ADP).
• Function: Serves as a structural component in bones and teeth in the form of calcium phosphate.

In the context of saponification of cardiolipins, breaking ester bonds in phosphate moieties releases inorganic phosphate, which becomes part of the solution's ionic milieu.