Cell Membranes

Understanding Cell Membranes

• A cell membrane (also known as the plasma membrane) is a thin structure that surrounds a cell and regulates what enters and leaves the cell.
• It’s composed of a phospholipid bilayer, with the heads being hydrophilic (water-loving) and the tails being hydrophobic (water-hating).
• It is a semi-permeable membrane, allowing only select substances to pass through.
• Integral proteins and peripheral proteins are embedded in the phospholipid bilayer, facilitating various cell functions.
• Cholesterol molecules are included to provide fluidity and stability.

Structure of Cell Membranes

• Phospholipids are arranged in a bilayer, with their hydrophobic (water-hating) tails pointing inwards, away from water and hydrophilic (water-loving) heads pointing outwards.
• The fluid mosaic model is a description of the cell membrane structure with proteins scattered throughout like tiles in a mosaic.
• Glycolipids and glycoproteins reside on the cell’s surface, playing roles in cell recognition and membrane stability.
• Protein channels and carrier proteins allow transport of substances that can’t diffuse through the lipid bilayer.

Function of Cell Membranes

• The primary role of the cell membrane is to control what enters and leaves the cell.
• It protects the internal components of the cell from the external environment.
• Facilitates passive transport (like diffusion and osmosis) and active transport (requiring energy) of substances in and out of the cell.
• It provides a site for signal transduction, allowing cells to respond to external stimuli.
• Allows cell recognition, cell signalling, and cell adhesion.

Cell Membranes and Disease Processes

• Many diseases involve malfunctions at the cellular level, especially concerning the cell membrane.
• In cystic fibrosis, a gene fault alters a protein involved in moving salt in and out of cells, affecting the fluidity of mucus on the lungs and other surfaces.
• In the case of diabetes, the insulin receptors on the cell membrane malfunction, causing difficulties with glucose transport.
• Inherited cholesterol disorders can alter the functioning of lipid bilayer, disrupting various cell membrane processes.