5. Plasma Membranes

• Cholesterol molecules are embedded within the lipid bilayer, helping maintain its fluidity at different temperatures.
• The plasma membrane consists of phospholipids arranged with their hydrophilic heads facing outward and the hydrophobic tails forming an inner bilayer.
• The cell membrane is selectively permeable, allowing some substances to pass through while preventing others from doing so.
• The plasma membrane is selectively permeable to certain substances due to the presence of proteins that act as channels or pumps.
• Protein channels allow specific molecules to pass through the membrane without being actively transported by carrier proteins.
• Carrier proteins bind with specific molecules on one side of the membrane and release them on the other side.
• Phospholipids have two fatty acid chains attached to glycerol via ester bonds.
• One end of the phospholipid is polar (hydrophilic) due to the presence of oxygen atoms, while the other end is nonpolar (hydrophobic).
• Proteins can be found on both sides of the membrane, including integral proteins that span across it and peripheral proteins attached to one side.
• In water, the hydrophilic ends face outwards towards the surrounding environment, while the hydrophobic ends form the interior of the cell.
• Cell Surface membranes control the movement of substances into and out of a cell. They are a recognition site for the body’s immune system, and they are the site of cell-cell communication.
• Cell signalling


  The process that leads to communication and coordination between cells.
• What is the function of glycoprotein molecules on the cell surface membrane?


  They are receptor sites for hormones and drugs, and cell signalling. They also stabilise the membrane by forming H bonds with water.
• What is the function of cholesterol?

  Cholesterol disrupts the close packing of phospholipids, affecting membrane fluidity and enhancing stability. It also increases the impermeability of membranes to ions and polar molecules.