2.3 - Transport across membranes Flashcards
Describe the fluid mosaic model of membranes
Fluid : phospholipid bilayer in which individual phospholipids can move = membrane has flexible shape
Mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded
Explain the role of cholesterol and glycolipds in membranes
Cholesterol: steroid molecule in some plasma membrane; connects phospholipids and reduces fluidity to make bilayer more stable
Glycolipds: cell signalling and cell recognition
Explain the function of extrinsic and instrinsic proteins in membranes
Extrinsic: binding sites/receptors e.g. hormones
Antigens (glycoproteins)
Bind cells together
Involved in cell signalling
Intrinsic:
electron carriers(respiration/photosynthesis)
Channel proteins (facilitated diffusion)
Carrier proteins (facilitated diffusion/ active transport)
Chan
Explain the function 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 environment
Selectively permeable to regulate transport of substances
Involved in cell signalling/ cell recognition
Name and explain 3 factors that affect membrane permeability
Temperature: high temperature denatures 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 colorimetry could be used to investigate members e permeability
- Use plant tissue with soluble pigment in vacuole. Tonoplast and cell surface membrane distrusted = increas permeability = pigment diffuses into solution
- select colorimetry filter with complementary colour
- use distilled water to set colorimetry to 0 measure absorption/ % transmission value of solution
- High absorbance/ low transmission = more pigment in solution
Define osmosis
Water diffuses across semi-permeable memebranes from an area of higher water potential to an area of lower water potential until dynamic equilibrium is established
What is water potential
Pressure created by water molecules measures in kPa
Water potential of pure water at 25 degrees Celsius and 100kPa is 0
More solute = water potential is more negative
How does osmosis affect plant and animal cells?
Osmosis into cell
Plant: protoplast swells = cell turgid
Animal: lysis
Osmosis OUT of cell:
Plant: protoplast shrinks = cell flaccid
Animal: crenation
Suggest how a student could produce a desired concentration of solution from a stock solution
Volume of stock solution = required concentration X final volume needed / concentration of stock solution
Volume of distilled water = final volume needed - volume of stock solution
Define simple diffusion
Passive process requires no energy from ATP hydrolysis
Net movement of small, lipid-soluble molecules directly through the bilayer from an area of high concentration to an area of lower concentration
Define facilitated diffusion
Passive process
Specific channel or carrier proteins with complementary binding sites transport large and/ or polar molecules/ ions (not soluble in hydrophobic phospholipid tail) down concentration gradient
Explain how channel and carrier proteins work
Channel: hydrophilic channels bind to specific ions = one side of the protein closes and the other opens
Carrier: binds to complementary molecule = conformational change releases molecule on other side of memebrane; in facilitated diffusion, passive process; in active transport, requires energy from ATP hydrolysis
Name 5 factors that affect the rate of diffusion
Temperature Diffusion distance Surface area Size of molecule Difference in concentration
State ficks law
Surface area X difference in concentration/ diffusion distance
How are cells adapted to maximise the rate of transport across their membrane
Many carrier/channel proteins
Folded membrane increases surface area
Explain how the difference between the shape of a graph concentration (X-axis) against rate (Yxaxis) for simple vs facilitated diffusion
Simple diffusion: straight diagonal line; rate of diffusion increases proportionally as concentration increases
Facilitated diffusion: straight diagonal line later levels off when all channel/carrier proteins are saturated
Define active transport
Active process: ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape
Specific carrier protein transports molecules/ions from area of low concentration to area of higher concentration
Compare and contrast active transport and facilitated diffusion
Both may involve carrier proteins
Active transport requires energy from ATP hydrolysis; facilitated diffusion is a passive process
Facilitated diffusion my also involve channel proteins
Define Co-transport
Movement of a substance against its concentration gradient is coupled with the movement of another substance down its concentration/ electrochemical gradient
Substances bind to complementary intrinsic protein: symport:transport substances in same direction
Antiport:transports substances in opposite direction e.g. sodium-potassium pump
Explain how co-transport is involved in the absorption of glucose/amino acids in the small intestine
- Na+ actively transported out of epithelial cells and into bloodstream
- Na+ concentration lower in epithelial cells than lumen of gut
- transport of glucose/amino acids from lumen to epithelial cells is ‘coupled’ to facilitated diffusion of Na+ down electrochemical gradient
