Biological Membranes Lecture 3

Study Notes

Membranes serve as a selective barrier for individual cells and organelles (e.g., nuclear envelope, mitochondrial membrane).
Cell membrane facilitates controlled transport of molecules, with specific receptors for substances like hormones.
Mitochondrial membranes also function in energy production.

Lipids: Most abundant macromolecules; form the main structure of membranes, including phospholipids, cholesterol, and glycolipids.
Proteins: Essential for biological functions; enable transport and serve as receptors.
Carbohydrates: Present as glycoproteins and glycolipids, located externally on cell membranes.

Phospholipids: Composed of hydrophilic heads (phosphate groups) and hydrophobic tails (hydrocarbon chains), arranged in bilayer formation in aqueous solutions.
Cholesterol: Intercalates between phospholipids, enhancing membrane stability and fluidity.
Glycolipids: Have carbohydrate portions facing outward, playing roles in cell recognition and signaling, including blood group antigens.

Integral Proteins: Include transmembrane and lipid-anchored proteins; essential for communication and transport across the membrane.
Peripheral Proteins: Located on the cytosolic side, indirectly attached to lipids, involved in maintaining cell shape and signaling.

Integral Proteins: Act as receptors, ion channels, and transport proteins facilitating the movement of molecules.
Peripheral Proteins: Include cytoskeletal proteins for structural stability and enzymes for signaling processes.

Glycolipids and Glycoproteins: Involved in cell-to-cell interactions; glycophorin exemplifies an integral glycoprotein vital for blood group recognition and fertilization.

Bilayer Arrangement: Two lipid leaflets with polar groups facing aqueous environments and nonpolar tails oriented inward.
Fluidity: Lipid movement depends on the saturation of fatty acids; allows lateral, rotational, and some transverse movements, contributing to membrane dynamics.
Stability: Cholesterol molecules provide stability and support despite overall fluidity.
Asymmetry: Distinct functions and orientations for outer and inner membrane leaflets due to unequal distribution of components.
Fluid Mosaic Model: Describes the dynamic nature of membrane components that can move laterally, presenting a mosaic of different structures.
Lipid Rafts: Specialized regions enriched with cholesterol and glycosphingolipids; confer rigidity and play roles in transport, endocytosis, and signal transduction.