Biochemistry: Phospholipid Structure and Function

Phospholipids and Membrane Structure

• Third hydroxyl (OH) group of glycerol is esterified to a polar or charged group, resulting in an amphipathic molecule.
• Phospholipids self-assemble into sheets, spheres, and vesicles in the presence of water and salts.
• The fatty acids attached to glycerol influence membrane fluidity and curvature, facilitating cell membrane formation.
• Cholesterol is exclusive to eukaryotic membranes and enhances membrane stability.
• Integral membrane proteins reside within the hydrophobic lipid bilayer, functioning mainly as channels for selective uptake of compounds.

Fatty Acid Metabolism

• In eukaryotic cells, fatty acids are metabolized in mitochondria, while prokaryotic bacteria metabolize them in the cytoplasm.
• Fats are digested in the gut and broken down by lipases into free fatty acids and glycerol, which then enter the bloodstream.
• Fatty acids are transported into cells via fatty acid transporters, which are integral membrane proteins.

β-Oxidation Process

• β-oxidation is the primary pathway for lipid degradation, focusing on the breakdown of fatty acids.
• Fatty acids, characterized by long carbon chains and a hydrophilic carboxylate group, vary in chain length, commonly C16 and C18.
• Triacylglycerols consist of three fatty acids esterified to glycerol and are the main form of fat storage.
• Adipocytes store fatty acids, which are reassembled into triacylglycerols through esterification.

Trans Fatty Acids and Health Implications

• Trans fatty acids are less common naturally; they arise from the partial hydrogenation of unsaturated fatty acids for solid consistency and shelf-life enhancement.
• Epidemiological studies link trans fat consumption to a higher risk of heart disease.

Functions of Fatty Acids

• Fatty acids serve as energy sources and carbon compounds, as well as crucial components of cellular membranes.
• Triacylglycerols act as storage forms of fatty acids in cells, with only two fatty acid chains present in membrane structures.

Coenzyme A and Fatty Acid Activation

• Fatty acids are activated through the formation of high-energy thioester bonds with Coenzyme A (CoA).
• FadD protein uses ATP to bind fatty acids to CoA, preparing them for oxidation.
• Acetyl CoA is a critical molecule in metabolic reactions, and the thiol group in CoA is necessary for forming thio esters with carboxylic acids.

Mitochondrial Transport of Fatty Acids

• Fatty acyl CoA must cross two mitochondrial membranes for metabolism.
• It is converted to a carnitine derivative for transport across membranes; once inside the mitochondria, carnitine is replaced by CoA to regenerate fatty acyl CoA.

β-Oxidation Cycle Overview

• The first step uses FAD as a cofactor to create a double bond in the fatty acid chain.
• The second step involves the addition of water, forming a hydroxyl group at the beta position.

Explore the fascinating world of phospholipids, essential components of cell membranes. This quiz delves into how their amphipathic nature and fatty acid composition influence membrane fluidity and structure. Test your knowledge of the roles phospholipids play in cellular organization.