transport across membranes

• label the plasma membrane

  1. phospholipid bilayer
  2. glycoprotein
  3. glycolipid
  4. extrinsic proteins
  5. intrinsic proteins
  6. cholesterol

  
• why is a diagram of the plasma membrane called 'fluid-mosaic'?

  fluid: proteins and phospholipids can move freely within the membrane

  mosaic: different proteins embedded in the phospholipids
• what is the function of a phospholipid bilayer?

  • allows small, non-polar, lipid soluble molecules to pass through
  • prevent polar, non-lipid soluble products from passing through
  • makes the cell membrane flexible
• the centre of a phospholipid bilayer is...

  hydrophobic so water soluble products can't pass through
• what is the purpose of cholesterol in the plasma membrane?

  providing stability
• how does cholesterol provide stability?

  cholesterol binds to the fatty acid tail, causing them to become closer together, preventing movement and also reducing fluidity of the membrane. It also prevents polar molecules (water) from passing through
• what type of proteins are there in the plasma membrane?

  intrinsic and extrinsic
• what are intrinsic proteins?

  intrinsic proteins are embedded through both sides of phospholipid bilayer (e.g. channel and carrier proteins)
• what do intrinsic proteins transport?

  polar and non-lipid soluble products
• what are extrinsic proteins?

  extrinsic proteins are present on only one side of the plasma membrane
• what do extrinsic proteins do?

  they provide mechanical support, they can bind to carbohydrates or lipids (to make glycoproteins and glycolipids) used for cell recognition and they act as receptors
• what type of proteins are channel and carrier proteins?

  intrinsic proteins
• what do channel proteins transport?

  channel proteins (fill with water) allow water-soluble ions to diffuse. The proteins can be gated and only open and/or shut
• what do carrier proteins transport?

  carrier proteins bind to larger molecules e.g. amino acids, glucose and change shape to carry them to the other side of the membrane
• what are the similarities between channel and carrier proteins?

  .

  • both intrinsic proteins
  • both are specific and have a specific tertiary structure
• what is a phospholipid bilayer made from?

  phospholipids which consist of TWO hydrophobic tails and a hydrophilic head.

  the phospholipids arrange themselves in a bilayer, tails facing inwards (away from water) and heads are facing out (towards water)
• what are glycoproteins?


  proteins attached to a carbohydrate, they also act as receptors
• what are glycolipids?


  lipids attached to a carbohydrate
• what is the definition of diffusion?

  the net movement of particles from an area of high to low concentration
• what is simple diffusion?

  when molecules diffuse directly across the cell membrane e.g. oxygen and carbon dioxide
• what molecules can pass through via simple diffusion?

  small molecules: can pass through spaces between the phospholipids

  non-polar molecules: they can dissolve in the hydrophobic core
• what type of process is simple and facilitated diffusion?

  a passive process
• what factors affect the rate of simple diffusion?

  • concentration gradient
  • thickness of exchange surface: particles travel less if there is a thin exchange surface
  • surface area: large surface area means more particles can diffuse at once
  • temperature: high temp means more kinetic energy and faster diffusion
• what is facilitated diffusion?

  when large or polar molecules can't diffuse directly across, instead they diffuse into carrier/channel proteins (which are highly specific, allowing only one or two molecules to pass through)
• how does facilitated diffusion occur?

  1. a large molecule attaches to a carrier protein
  2. causing the carrier protein to change shape
  3. carrier protein releases molecule on opposite side of the membrane
• what do carrier proteins transport?

  large molecules
• what are channel proteins and what do they carry?

  channel proteins form pores in the plasma membrane and they transport ions
• what factors affect the rate of facilitated diffusion?

  concentration gradient and the number of channel/carrier proteins
• what is the definition of osmosis?

  the movement of water from an area of a higher water potential to an area of lower water potential across a partially permeable membrane
• what is water potential?

  water potential is the pressure exerted by water molecules on the membrane or container surrounding a solution
• high water potential means...

  solution has a higher concentration of water than solute
• low water potential means...

  there is a lower water concentration than solute
• water potential

  
• how does osmosis occur?

  water molecules are small so can diffuse directly across the cell membrane whereas solute molecules can't. water diffuses until equilibrium is reached (same water potential on both sides)
• what is a hypertonic solution?

  a solution with higher water potential inside cell than in the solution
• what is an isotonic solution?

  a solution where water potential is the same inside and outside the cell
• what is a hypotonic solution?

  a hypotonic solution has a lower water potential inside the cell than the solution
• what happens to both animal and plant cells in a hypertonic solution?

  • both cells have a higher water potential inside the cell, therefore causing water to move out and causing the cell to shrink
  • plant cell becomes PLASMOLYSED
• what happens to animal and plant cells in isotonic solutions?

  there is no net movement of water
• what happens to animal and plant cells in a hypotonic solution?

  water moves into the cell, making it swell

  animal cells burst whereas plant cells become turgid as it doesn't burst due to its cell wall