Transport across membrane Flashcards
(21 cards)
Describe the fluid mosaic model of membranes
Fluid:Phospholipid bilayer in which individual phospholipids can move=membrane has flexible shape
Mosaic:Extrinsic and intrisinic proteins of different size and shapes are embedded
Explain the role of chloestrol and glycolipids in membranes
Chloesterol:Steriod molecule in some plasma membranes;connects phospholipids and reduces fludity to make bilayer more stable
Glycolipids:Cell signalling and cell recognition
Explain the functions of extrinsic and transmembrane proteins in membranes
Exteinsic:
* binding sites/receptors e.g for hormones
* Antigens (glycoproteins)
* binds cells together
* involved in cell signalling
Intrinsic:
* electron carriers (respiration/photosynthesis)
* channel proteins (facilitated diffusion)
* carrier proteins (facilitated diffusion/ active transport)
Explain the functions of membranes within cells
- provide internal transport system
- selectively permeable to regulate passage of molecules into/out of organelles
- provide reaction surface
- isolate organelles from cytoplasm for specific metabolic reactions
Explain the functions of the cell surface membrane
isolates cytoplasm from extracellular enviroment
selectively permeable to regulate transport of substances
involved in cell signalling recognition
Name 3 factors that affect membrane permeability
- temperature: high temperature dentaures membrane proteins/phospholipid molecules have more kinetic energy and move further apart
- Ph: changes tertiary structure of membrane proteins
- use of a solvent: may dissolve membrane
Outline how Colorimetery can be used to investigate membrane permeability
- Use Plant tissue with soluble pigement in vacuole. Tonoplast and cell surface membrane disrubted= increase permeability =pigment diffuses into solution
- select colorimeter filter with complementary colour
- use distilled water to set colirmeter to 0. measure absorbance/ % transmission value of solution.
- High absorbance/lowtransmission =more pigment in solution
Define Osmosis
Transport of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential until a dynamic equilibrium is established
How does Osmosis affect plant and animal cells
-
Osmosis into cell Plant protoplast swells=cells turgid
animal: lysis (breaking of cellmembrane release of cellular components) - Osmosis out of cell: Plant:protoplast shrinks=cell flaccid
- animal:crenation (shrinkage of cell causing it to wrinkle and condense)
Define simple diffusion
Net movement of small lipid-soluble molecules directly through the bilayer from an area of high concentration to an area of lower concentration (down conc gradient)
Passive process requires no energy from ATP hydrolysis
Define Facilitated Diffusion
Specific channel or carrier proteins with complementary binding sites transport large and polar molecules/ions down concentration gradient
Passive process:requires no ATP
Explain how channel and carrier proteins work
channel:Form tubes filled with water and this enables water soluble ions to pass through membrane. Hydrophillic channels bind to specific ions=one side of protein closes and the other opens
Carrier:Binds to complementary molecule=conformational change releases molecule on other side of membrane
(in fd passive ) (in at requires atp hydrolysis)
5 Factors that affect rate of diffusion
- temperature
- diffusion distance
- surface area
- size of molecule
- difference in conc gradient (how steep conc gradient is)
State Ficks Law
Surface area xdifference in conc/diffusion distance
How cells adapted to maxmise the rate of transport across their membranes
- mny carrier proteins/channel proteins
- folded membrane increase surface area
- lots of mitrochondria for energy release atp hydrolyisis
- micro villi
Explain the difference between the shape of graph of concentration (x-axis) against rate (y-axis) for simple vs facilitated diffusion
- Simple diffusion:straight diagonal line; rate of diffusion increases proportionally as conc increases
- Facilitated diffusion: Straight diagonal line later levels of when all channel/carrier proteins are saturated
Define active transport
Active Process ATP hydrolysis releases phosphate groups that bind to carrier protein causing it to change shape
Specific carrier protein transports molecules/ions from area of low conc to an area of high conc (against conc gradient)
Movement of molecules and ions from an area of lower concentraition to an area of higher concentration (against conc gradient) using ATP and carrier proteins. the carrier protein acts as a pump to move substances across the membrame. very selective as only certain moleducles can bind to carrier proteins
Define Co-transport
Movement of a substance against its conc gradient is coupled with movement of another substance down its conc/electro chemical gradient
Substances bind to complementary intrinsic protein:symport transports in same direction antiport: transports substances in opposite direction e.g sodium ppotassium pump
Describe how co-transport is involved in the absoptioon of glucose/amino acids in the small intestine
- Na+ transported out of epithelial cells and into the blood stream. this reduces the concentration in epithelial cell
- Na+ concentration is lower in epithelial cells than lumen of gut. so NA+ can diffuse from the lumen into epithelial cells
- protein the sodium ions diffuse through is co transported protein. glucose/amino acids also attacth and are transported into the epithelial cell against conc gradient
- transport of glucose/amino acids from lumen to epithelial cells is ‘couples’ to facilitated diffusion of Na+ down electrochemical gradient
- glucose then moves by faciltated doffusion from epithelial cells to the blood.
What is an isotonic, hypertonic and hypotonic solution
Isotonic- when water potential is the same in the solution and the cell within the solution.
hypotonic- when the water potential of a solution is more positivie (closer to 0) than the cell.
hypertonic-when the water potential of a solution is more negative than the cell.
Describe in detail active transport
- transport through carrier proteins
- molecule binds to a receptor complementary in shape on the protein
- atp binds to the carrier protein from the inside of thce cell and is hydrolysed into ADP+PI
- this causes the carrier protein to change shape and release the molecule to the other side
- the phosphate ion is then released and the protein returns to its orginal shape.
