Biological membranes

• role of the partially permeable membrane 


  allows some substances to pas freely but prevents the passage of others (these will need transport proteins)
• role of the selectively permeable membrane 


  presence of specific transport proteins determines which substances can cross
• why are the properties of membranes important 


  allows membranes to form a barrier and separate contents of cell or organelle from its environment and determine which substances can enter or leave
• roles of the plasma membrane (cell surface)

  can they separate cell contents from its external environment 


  yes
• roles of the plasma membrane (cell surface)

  can they control transport substances into or out of the cell 


  yes
• roles of the plasma membrane (cell surface)

  can they do bulk movement of substances into or out of the cell by endocytosis or exocytosis 


  yes
• role of plasma membrane:

  are they the location of antigens for cell recognition as 'self' or 'non-self' 


  yes
• role of plasma membrane:

  do they contain receptors for intracellular recognition and signalling 


  yes
• role of plasma membrane:

  do they have cell to cell attachment to form tissues 


  yes
• role of plasma membrane:

  do they protect the rest of the cell from contents 


  yes
• role of internal membrane:

  do they separate organelle contents from cytoplasm 


  yes
• what are the components of the plasma membrane: 


  • actin microfilament
  • extrinsic protein
  • phospholipid bilayer
  • cholesterol
  • glycolipid
  • channel protein
  • glycoprotein
• what is the difference between intrinsic and extrinsic proteins:

  intrinsic proteins are embedded in the phospholipid bilayer and often span the bilayer

  extrinsic proteins are on the surface of bilayer but are associated with one side of the membrane
• definition of a phospholipid bilayer

  phospholipids form a bilayer that is the structural basis of all membranes, they provide a barrier to the movement of most polar molecules and ions. the other membrane components determine the properties and roles of the membrane.
• role of membrane components: cholesterol

  small molecules that fits in between the fatty acid tails and stabilises the membrane by binding to the fatty acid tails. controls the fluidity of the membrane and helps prevent polar molecules and ions crossing the membrane
• Role of transport proteins

  Act as channels or carriers to transport polar molecules and ions across the membrane via facilitated diffusion or active transport

  also act as enzymes
• role of phospholipid heads 


  Form a bilayer to protect their hydrophobic tails from the aqueous environment that is the basis of membrane structure

  Act as a barrier to the movement of polar molecules and ions but allow non-polar molecules to cross
• role of glycoproteins 


  proteins modified in the Golgi apparatus by the addition of carb chains

  act as antigens for cell recognition or non-self and act as receptors for chemical signals

  also help cell adhesion to form tissues
• role of glycolipids 


  lipds modified in the Golgi apparatus by the addition of carb chains

  Act as antigens for cell recognition and help cell adhesion to form tissues
• How does cholesterol affect membrane permeability 


  Low temp:prevents regular packing of phospholipids so prevents freezing

  high temp:interacts with non-polar phospholipids to maintain structure
• 3 external factors that affect membrane permeability 


  Temp

  Organic solvent

  Detergents
• What is relationship between temp and membrane permeability 


  As temp increases phospholipids gain more kinetic energy so move more
• Define passive transport 


  net movement occurs from an area of high conc to low conc

  Down a conc gradient

  Diffusion is a passive process since no additional energy is required
• define simple diffusion 


  small molecules fit in between hydrophobic fatty acid tails and pass through bilayer
• Define facilitated diffusion 


  Large polar molecules and ions cannot diffuse across the phospholipid bilayer and require a specific transport proteins
• What is a gated channel

  Are open or closed depending on the presence of another molecule or the potential difference across the membrane
• what is a carrier protein

  can bind a specific polar molecule on one side of the membrane and then change shape to release the molecule on the other side of membrane
• Role Of membranes 


  Control substances entering and leaving which allows division of labour
• role of plasma membrane

  surrounds cells and internal membranes

  form organelles by compartmentalisation (dividing a cell into compartments)
• role of the internal membranes

  Regulates the passage of nutrients/info in and out of the cytoplasm
• What is the role of cell membranes

  Form partially permeable barriers that separate the cell contents from its external environment and organelle contents from the cytoplasm
• difference between plasma and internal membranes

  plasma surrrounds cell to form organelles

  internal regulates the passage of nutrients and info in and out of the cytoplasm
• what is the role of the partially permeable membrane

  allows some substances to pass freely but prevents the passage of others (these would need transport proteins)
• role of the selectively permeable membrane

  presence of specific transport proteins determines which substances can cross
• more roles of plasma membrane

  separates cell contents from its external environment

  control transport of substances in/out of cell

  bulk movement of substances in/out of cell by endo or exo cytosis

  location of antigens for cell recognition as self/non-self

  contain receptors for intracellular recognition and signalling

  cell to cell attachment to form tissues

  protection of rest of cell from contents

  release of chemical signals to allow cell signalling
• More roles of internal membranes

  Separate organelles contents from cytoplasm

  Control transport of substances in/out of the organelle

  Formation of vesicles for intracellular transport

  Site of attachment for ribosomes

  Site of attachment and organisation of enzymes

  Site of chemical reactions

  Location of photosynthetic pigments for photosynthesis

  Protection of DNA in nucleus
• What are the components of the phospholipid bilayer

  Glycoprotein

  Extrinsic and intrinsic proteins

  Glycolipid

  Phospholipid

  Cholesterol
• what is the role of cholesterol in the phospholipid bilayer

  controls fluidity and prevents polar molecules and ions crossing the membrane
• what is the role of transport proteins

  act as channels and carriers to transport polar molecules and ions across the membrane

  also act as enzymes
• what is the role of the phospholipid head in the phospholipid bilayer

  protect their hydrophobic tails

  act as a barrier to the movement of polar molecules and ions but allow non-polar molecules to cross