plasma membranes

• what structure do all membranes have?

  fluid mosaic structure
• Why is the bilayer fluid?

  Phospholipids are constantly moving
• Phospholipid bilayer structure


  2 fatty acid chains attached to phosphate head
• are the fatty acid chains in phospholipids hydrophobic or hydrophilic?

  hydrophobic
• are the phosphate heads in phospholipids hydrophobic or hydrophilic?

  hydrophilic and polar
• where do cells normally exist?

  in aqueous environments
• 2 structures that phospholipids form when exposed to water

  micelle structure or phospholipid bilayer
• what do the fatty acid chains in phospholipids let through?

  fat soluble molecules - act as a barrier to water soluble molecules
• Cholesterol role in membrane

  Maintains the fluidity of the membrane
• how does cholesterol maintain the fluidity of the membrane?

  they bind to the tails of the phospholipids, making them pack less closely together
• which are more branched glycolipids or glycoproteins?

  glycoproteins
• glycolipid roles

  -stabilise the membranes

  -cell receptors

  - cell recognition

  - cell to cell attachment
• How do glycolipids stabilise the membrane?

  by forming hydrogen bonds with surrounding water molecules
• What are glycolipids?

  phospholipids with carbohydrate attached
• another name for glycoliclipids

  cell markers or antigens
• What are glycoproteins?

  proteins with carbohydrate attached
• Are glycoproteins intrinsic or extrinsic?

  intrinsic
• role of glycoproteins

  -receptors for hormones, neurotransmitters and enzymes

  - cell adhesion
• two types of intrinsic proteins

  protein channels and carrier proteins
• where are intrinsic proteins?

  span the width of the phospholipid bilayer
• what do intrinsic proteins have and how does it help?

  amino acids with hydrophobic R groups on external surfaces- help transport substances that can't diffuse through the membrane
• channel protein role

  provode hydrophillic channels that allows the movement od polar molecules and ions through membranes
• how are channel proteins held in shape?

  by the hydrophobic core of the membrane and hydrophobic R groups on there outside
• Role of carrier proteins

  move large molecules into or out of the cell- DOWN the concentration gradient
• Role of extrinsic proteins

  - cell signalling

  -chemical reactions

  -cell recognition

  -act as receptors for hormones or neurotransmitters
• Why is membrane fluidity important?

  - diffusion of substances across the membrane

  - helps membranes to fuse e.g during exocytosis

  - helps cells move and change shape
• Factors that affect membrane permeability and structure

  Temperature and solvents
• How does temperature affect membrane permeability?

  as the temperature increases, the kinetic energy of the phospholipids increase. this creates gaps between the bilayer- big gaps mean larger molecules can go through, so permeability increases
• at what temp do proteins begin to denature?

  40°C
• 3 ways substances can move into and out of cells


  diffusion, osmosis, active transport
• Diffusion definition

  the net movement of particles down a concentration gradient (from a region of high concentration to a region of low concentration)
• Is diffusion passive or active?

  passive (no energy required)
• ficks law

  rate of diffusion proportional to surface area and difference in concentration / length of membrane
• How to increase diffusion

  Increase surface area

  Increase temperature

  Make the distance travelled shorter

  Increase the concentration gradient
• how to decrease diffusion

  increase the distance
• What is simple diffusion?

  small non-polar molecules in a high concentration on one side of the membrane can easily pass through the bilayer
• examples of substances that diffuse through simple diffusion

  oxygen and carbon dioxide (lipid soluble molecule)
• facilitated diffusion definition

  large and/or polar molecules cannot cross straight through the bilayer- instead they use carrier and channel proteins
• examples of molecules that use facilitated diffusion

  glucose and amino acids
• active transport definition

  The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins