Cell Membrane Fluidity

Biological Membranes

• All biological membranes have a feature of fluidity, which is the ability to change shape and move in response to changes in temperature and other environmental factors.

Role of Cholesterol

• Cholesterol is present in the cell membrane and plays a crucial role in maintaining membrane fluidity by reducing the mobility of phospholipids at high temperatures and increasing their mobility at low temperatures.

Lipid Bilayer Structure

• The structure and flexibility of the lipid bilayer are determined by the properties of phospholipids, such as the length of their hydrocarbon chains and the presence of unsaturated fatty acids.
• The lipid bilayer is commonly measured using the black lipid membrane, which is a type of artificial membrane.

Phospholipid Movement

• Phospholipids can move from one leaflet of the lipid bilayer to the other through a process called flip-flop.

Factors Affecting Fluidity

• The fluidity of a lipid bilayer is affected by temperature, with higher temperatures increasing fluidity and lower temperatures decreasing it.
• The presence of unsaturated fatty acids and cholesterol also affects membrane fluidity.
• The length of the hydrocarbon chains of phospholipids does not affect the fluidity of the lipid bilayer.

Lipid Bilayer Phase Transition

• The change of a lipid bilayer from a liquid state to a two-dimensional rigid crystalline state is called a phase transition.

Elastin and Its Role

• Elastin is a protein responsible for giving tissues their elasticity, such as the skin, blood vessels, and lungs.
• The molecules of elastin are joined together by desmosine cross-links, which generate a cross-linked network.

Fibronectin and Its Role

• Fibronectin is a protein that plays an important role in tissue repair, cell attachment, and motility, as well as embryogenesis.

Basal Lamina and Extracellular Matrix

• The primary organizer of the sheet structure of the basal lamina is laminin.
• Cells are contained in a complex and intricate network of macromolecules known as the extracellular matrix (ECM), which is composed of collagen, elastin, and other proteins.
• The common functions of the ECM include providing mechanical support, regulating cell behavior, and facilitating cell-cell communication.

Connective Tissue

• Bone tissue is a type of connective tissue that consists of collagen fibers and bone mineral.
• Fibroblasts are the cells that produce and secrete the ECM in connective tissue, specifically collagen fibers.

Lipid Bilayer Fluidity

• At low temperatures, the lipid bilayer is more rigid and less fluid due to the increased ordering of the phospholipid tails.
• Unsaturated fatty acids decrease the melting point of the lipid bilayer, making it more fluid.
• Cholesterol increases the fluidity of the lipid bilayer by reducing the mobility of phospholipids at high temperatures and increasing their mobility at low temperatures.
• Cis-double bonds in hydrocarbon chains of membrane phospholipids increase the fluidity of the lipid bilayer by introducing kinks in the chain, making it more flexible.