membrane permeability

• 1. liposome
  2. micelle
  3. bilayer sheet

  
• Permeability refers to the ease with which molecules cross biological membranes.  Cell membranes allow only selective substances to enter or leave the cell. Permeability of cell membranes can be affected by different factors or conditions.
• Permeability of cell membranes can be affected by different factors or conditions.

  • temperature
  • solvents
• • When we increase temperature we increase the kinetic energy of the phospholipids
  • phospholipids are moving more so the membrane becomes more fluid and loses some of its structure
  • This reduces the effectiveness of the cell membrane as a barrier so polar molecules can pass through.
• Carrier and channel proteins will be denatured at higher temperatures and this will also increase permeability
• • Organic solvents like ethanol or benzene are non polar or less polar than water.
  • Non polar alcohol molecules can enter the cell membrane and wedge between the phospholipids. This disrupts the cell membrane structure
  • When disrupted  it becomes more fluid and essentially leaky - it becomes more permeable
• Why do we use alcohol based hand sanitizer?

  • Alcohol is non-polar and can insert itself into cell membrane and disrupts the cell membrane integrity of pathogens. This destroys them because the contents of the cell leaks out. (Alcohol also denatures proteins)
• Why do we wash our hands with soap?

  • Soap consists of a hydrophilic head and hydrophobic tail. It inserts itself into the cell membrane of pathogens disrupting them. When used for 20s or more the soap molecules form a micelle around the pathogen blocking it’s binding proteins. This also makes them easy to physically wash away with water.
• Neurotransmission relies on facilitated diffusion in neurones. Explain why excessive drinking can affect the nervous system.

  • If the membranes are disrupted the nerve impulses are no longer transmitted as normal