M2:T4: Membranes

• explain membranes

  • in all cells
  • larger molecules, ions and small charged atoms need specific transport
  • differentially permeable barrier separating inside and outside
  • small, neutrally charged moelcules transportable
• cytoplasmic membrane 


  has 3 things

  1. phospholipid bilAyer
  2. perphial proteins which attached to surface
  3. integral proteins which are integrated in membrane
• bacterial membrane

  • phospholipid bilayer
  • lipid
  • glyercol and 2fa with phosphate in photo lipid
  • DI-ESTER bonding
• eurkayral

  • phosophilid
  • provides backbone
  • STEROLS
  • needs extra strength as there is no cell wall
• archeal

  • glycerol is linked to phosphate or sulphate, carb or nothin
  • lipids are hydrocarbon
  • 4 different types of membranes
• monolayer


  lipid fuse together = extra strength
• bacteria membrane summary


  protein content: high

  lipid comp: phso

  lipid linkage: ester

  structure: bilayer

  sterol: no
• eukaryotic membrane summary


  protein content: low

  lipid comp: phso

  lipid linkage: ester

  structure: bilayer

  sterol: yes
• acheal membrane summary 


  protein content: high

  lipid comp: phso etc

  lipid linkage: ether

  structure: bilayer or mono

  sterol: no
• 3 functions of cell membrane

  1. permeability barrier: prevents leakage and nutrient transport
  2. proetin anchor: transport
  3. energy conservation: generation and dissipation
• passive transport

  • no energy is required
  • diffusion
  • facilitated diffusion
  • osmosis
  • travels down high to low []
• active transport

  • requires energy
  • active: membrane proteins
  • group translocation
  • ATP-binding cassette
• different types of transport proteins

  1. uniporter: 1 sub at a time, unidirectional
  2. symporter: 2 sub, sim and same direction
  3. Antiporter: opposite direction
• active transport 


  aerobic

  • ions
  • against []
  • uses proteins for transport
• group translocation

  • anaerobic and facultative pro
  • transported sub is chem alt
• ATP-binding cassette

  • gram -ve bacteria only
  • invalves uptake of organic compounds
• 2nd types of membrane

  • outer membrane
  • made from lipopolysaccharide and sometimes o-specific polysaccharides
  • lipoo: are highly toxic due to endotoxin when released
• prions 


  channels for movement of hydrophilic low mol weight subs

  found in outer meme
• why might sterillisation not be stopped

  due to lipa becoming rapid
• outer layer membrane in gram -ve contains 


  lipopolysaccharide
• plasmolyse is 


  cell loses water in hypertonic solution \
• what is true about the peripheral membrane proteins

  they are lossley attached to membrane bilayer
• lipid-soluble molcules cross the membrane in

  simple diffuision
• function of cyto mem

  • barrier to seperate and control
• importance of outer membrane in gram -ve

  • lipopolysacc contains o-antigens which protect against host defence
  • polysaccharides = attachement
  • lipA for exotoxin