Transport/Membranes Flashcards
Characteristics of phospholipids.
2 fatty acid, glycerol and a phosphate.
A hydrophobic tail and hydrophilic head so it forms a bilayer.
Characteristics of the cell membrane (plasma).
Partially permeable. Contain a phospholipid bilayer, intrinsic proteins on the span membrane extrinsic proteins on the surface, cholesterol for stability and glycolipids which are at the recognition site.
Characteristics of lipids
Lipid soluble molecules, water and other small molecules can diffuse through them. Water soluble ones ones and larger molecules
(e.g. Glucose) can’t.
Fluid mosaic model
Fluid means the molecules are moving
Mosaic means it is made up of proteins and phospholipids
Diffusion definition
The net movement of particles from an area of high to low concentration. It is a passive process so it moves down the concentration gradient.
Diffusion is quicker when…
There is a bigger surface area, shorter diffusion path, higher temperature and bigger concentration gradient.
A higher temperature gives particles more kinetic energy so they move faster. Therefore faster diffusion.
Facilitated diffusion
When a molecule (e.g. Glucose) is too large to diffuse across the membrane but it can go via protein carriers/channels.
It is similar to diffusion (both passive) but involves proteins that are specific to the substance crossing.
Carrier proteins in facilitated diffusion
Carrier proteins may become the limiting factor in facilitated diffusion. This is due to them being fully saturated with molecules meaning it can’t carry anymore across the membrane.
Osmosis
The net movement of water particles from an area of high concentration to low, across a partially permeable membrane.
It is a passive process, there are no carrier proteins and it is down the concentration gradient.
Water moves to a more negative water potential. Meaning the more concentrated the solution is the lower the water potential is.
Animal cells in hypotonic solution may burst. In isotonic they stay the same. In hypertonic they shrink.
Active transport
It is the net movement of molecules/ions from an area of low concentration to an area of high concentration using energy and carrier proteins.
It requires ATP and therefore lots of mitochondria. It uses carrier proteins for this.
It is against the concentration gradient.
How substances move across the membrane via carrier proteins using active transport:
1) The ion binds to a carrier protein on receptor sites
2) On the inside of the membrane, ATP binds to the protein and is then hydrolysed to form ADP and Pi
3) This causes the protein to change shape and open to the other side
4) The ion is released
5) Pi is released from the protein, so it changes back to it’s original shape
Active transport in glucose absorption
It helps all the glucose to be absorbed. Through co-transport which uses 2 molecules.
1) Sodium ions are actively transported from the ileum epithelium cell to the blood by the Na/K pump (sodium potassium pump)
2) It maintains/forms a diffusion gradient for sodium ions to enter cells from the gut (with glucose)
3) Glucose enters by facilitated diffusion through the co-transport of sodium ions.
