MCAT Biochemistry
Structural lipids are major components of the cell membrane, and their amphipathicity allows the cell to form a barrier between the cell and the environment. They also enable the cell to regulate what is allowed in and out. The characteristics of structural lipids contribute to the fluidity of the membrane. Phospholipids are structural lipids with a phosphate head and alcohol backbone. Those with a glycerol backbone are glycerophospholipids, and those with a sphingosine backbone are sphingophospholipids.
Structural lipids with a sphingosine backbone but no phosphate are the sphingolipids, which include ceramides, sphingomyelins, glycosphingolipids like cerebrosides and globosides, and gangliosides. Lastly, waxes consist of a long chain fatty acid attached to a long chain alcohol and serve a protective function. They are extremely hydrophobic and are not typically found within the cell membrane.
Lesson Outline
<ul> <li>Structural Lipids <ul> <li>Major components of the cell membrane</li> <li>Amphipathicity</li> <li>Types: Phospholipids, Sphingolipids, Waxes</li> </ul> </li> <li>Membrane Fluidity Factors <ul> <li>Degree of saturation</li> <li>Structure of double bonds</li> <li>Length of fatty acid chains</li> </ul> </li> <li>Phospholipids <ul> <li>Contain a phosphate bonded to an alcohol</li> <li>Classified based on the alcohol backbone</li> <li>Types: Glycerophospholipids, Sphingophospholipids</li> </ul> </li> <li>Glycerophospholipids <ul> <li>Built on a glycerol backbone</li> <li>Two fatty acid tails bonded to glycerol by ester linkages</li> <li>Phosphate attached to glycerol by phosphodiester bonds</li> <li>Head groups determine membrane surface properties</li> </ul> </li> <li>Sphingolipids <ul> <li>Sphingosine backbone</li> <li>One fatty acid tail bonded to sphingosine by amide linkage</li> <li>Types: Sphingophospholipids, Ceramides, Glycolipids (Glycosphingolipids)</li> </ul> </li> <li>Sphingophospholipids <ul> <li>Examples: Sphingomyelins</li> <li>Significance: Major component of myelin in nervous system</li> </ul> </li> <li>Glycosphingolipids <ul> <li>Bonded to sugar molecules</li> <li>Types: Cerebrosides (one sugar), Globosides (two or more sugars), Gangliosides (oligosaccharide and sialic acid)</li> <li>Significance: ABO blood typing system (globosides), cell recognition and signal transduction (gangliosides)</li> </ul> </li> <li>Waxes <ul> <li>Hydrophobic</li> <li>Consist of long-chain fatty acid attached to long-chain alcohol</li> <li>Function: Protection against evaporation, dehydration, and parasites</li> </ul> </li> </ul>
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FAQs
Structural lipids play a crucial role in maintaining the integrity, flexibility, and functionality of the cell membrane. They provide a barrier between the cell and its surroundings, protect cellular components, and contribute to membrane fluidity. Key structural lipids include phospholipids, glycerophospholipids, sphingolipids, and waxes, which together form the lipid bilayer of the membrane, ensuring a stable environment for cellular processes.
Phospholipids possess a polar (hydrophilic) head and nonpolar (hydrophobic) tail, giving them their amphipathic nature. The hydrophilic heads are attracted to water, while the hydrophobic tails repel water. In the cell membrane, phospholipids arrange themselves in a bilayer, with the hydrophilic heads facing the aqueous environments both inside and outside the cell, while the hydrophobic tails face each other, creating a barrier that separates the cell from its environment and regulates the passage of substances across the membrane.
Glycerophospholipids and sphingolipids are two types of structural lipids found in the cell membrane. Glycerophospholipids are composed of a glycerol backbone, two fatty acid chains, and a phosphate group with a polar head group. In contrast, sphingolipids contain a sphingosine backbone instead of a glycerol backbone, one fatty acid chain, and a polar head group. Both types of lipids contribute to the integrity and function of the cell membrane, and they each have specific roles in cell signaling, recognition, and membrane stability.
Membrane fluidity is essential for proper cell function, as it influences processes such as cell signaling, membrane protein function, and nutrient transportation. The structural lipids in the cell membrane, especially phospholipids, help maintain fluidity by providing lateral movement of lipids and proteins within the bilayer. Variations in fatty acid chain lengths and degrees of unsaturation within these structural lipids also impact fluidity. For example, longer chains with more saturation tend to decrease fluidity, while shorter chains and higher levels of unsaturation increase fluidity by reducing the tight packing of fatty acids.
Waxes, which consist of long-chain fatty acids esterified to long-chain alcohols, are considered structural lipids due to their role in membrane stability and integrity. Although waxes are not typically a component of the cell membrane, they may be found on the surface or in specialized regions of some cell types, where they contribute to membrane rigidity and serve as a protective barrier against water loss or the entry of harmful substances. Additionally, waxes are often involved in the external protection of organisms, such as in the waterproofing of plant leaves or the exoskeletons of insects.
