Membrane permeability

• Self-assembly


  The natural tails-in heads-out configuration that phospholipids assume when in an aqueous solution
• The colder it gets, the denser and more rigid the cell membrane is. The warmer it gets, the more fluid
• If it gets too cold, the cell membrane gets too rigid and might break. If it gets too hot, the cell membrane might be too fluid and fail to hold shape. Cholestorol helps the cell membrane keep its shape and be more resistant to changes in temperature
• Cholesterol


  Randomly distributed steroid molecules that hold phospholipids in place so that they don't have large gaps (letting unwanted things in) or get too close together (restricting movement across the membrane)
• Fluid mosaic model


  The cell membrane structure: when molecules move like a fluid across a 2D plane
• Increased space from unsaturated fatty acid tails lets smaller molecules, like CO2 and O2, get in through the cell membrane
• Small nonpolar molecules


  Can easily pass through the cell membrane without help from proteins because, due to their size, they can squeeze through the phospholipids
• Small polar molecules


  Can squeeze through the cell membrane because of their size, but do it slowly because of their charge
• Large nonpolar molecules


  Can pass through the cell membrane but it's a long process because of their size
• Large polar molecules


  Their size and charge make it too difficult for them to pass through the nonpolar regions of the phospholipid membrane without the help of a transport protein
• Ions


  Their charge makes it too difficult for it to pass through the phospholipid membrane without the help of a transport protein
• Extracellular matrix (ECM)


  Complex meshwork of proteins and carbohydrates that makes up the space outside of cells
• Collagen


  A protein that is a major component of the extracellular matrix, and plays a key role in giving tissues strength and structural integrity
• Collagen fibrils


  Long strands of collagen proteins modified with carbohydrates that were released out of cells
• Glycosilation


  When a carbohydrate is covalently bonded to a large target macromolecule, typically a protein or lipid
• Proteoglycans

  Heavily glycosilated proteins
• In the extracellular matrix, collagen fibers are interwoven with proteoglycans, which may be attached to a long polysaccharide backbone
• Integrins


  Proteins embedded into the plasma membrane that connect the cell to the extracellular matrix, and can detect both chemical and mechanical cues from the extracellular matrix and trigger signalling pathways in response
• Fibronectin


  Protein that acts as a bridge between integrins and other parts of the ECM like collagen
• Tissue factor


  A protein receptor on the cells lining a blood vessel that is displayed when they are damaged. As soon as it binds to a molecule present in the ECM, it triggers a bunch of reactions to stop blood loss, like sending platelets to stick to the wall and produce clotting factors
• Instead of collagen as an extracellular structure to give them structure, plants have the cell wall
• Cell wall


  Rigid covering that surrounds a plant cell that is mostly made out of cellulose, giving it shape and support.
• All plants and fungi, most prokaryotes, and some protists have a cell wall
• Cellulose


  Polysaccharide composed of glucose units that assembles into microfibrils to form the majority of the cell wall
• Microfibril


  Very fine fibre-like strand composed of cellulose, in the case of the cell wall
• Middle lamella


  Sticky top layer of the cell wall that helps hold the cell walls of adjacent plant cells together