Transport across membranes (4) Flashcards
What is meant by ‘fluid’ in the fluid mosaic model of membranes?
phospholipid bilayer in which individual phospholipids can move causing membrane to have a flexible shape
What is meant by ‘mosaic’ in the fluid mosaic model of membranes?
extrinsic and intrinsic proteins of different sizes and shapes are embedded
What is the role of cholesterol in membranes?
steroid molecule in some plasma membranes which connects phospholipids and reduces fluidity to make bilayer more stable
What is the role of glycolipids in membranes?
cell signalling and cell recognition
What do extrinsic proteins contain?
binding sites/receptors
antigens (glycoproteins)
What are the 2 functions of extrinsic proteins in membranes?
- bind cells together
- involved in cell signalling
What do intrinsic proteins contain and what are these for?
- electron carriers (for respiration and photosynthesis)
- channel proteins (facilitated diffusion)
- carrier proteins (active transport/facilitated diffusion)
What are the 4 functions of a membrane?
- 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
What are the 3 functions of a cell-surface membrane?
- isolates cytoplasm from extracellular environment
- selectively permeable to regulate transport of substances
- involved in cell signalling/cell recognition
What are 3 factors affecting membrane permeability?
1) temperature
2) pH
3) use of solvent
How does temperature affect membrane permeability?
high temperature denatures membrane proteins and phospholipid molecules have more kinetic energy and move further apart
How does pH affect membrane permeability?
changes tertiary structure of membrane proteins
How does the use of a solvent affect membrane permeability?
may dissolve membrane
What are the 4 steps on how colorimetry can be used to investigate membrane permeability?
1) use plant tissue with soluble pigment in vacuole (tonoplast cell-surface membrane disrupted, increasing permeability so pigment diffuses into solution)
2) select colorimeter filter with complementary colour
3) use distilled water to set colorimeter to 0 and measure the absorbance/% transmission value of the solution
4) high absorbance/low transmission means there is more pigment in the solution
What is meant by osmosis?
water diffuses across semi-permeable membranes from an are of higher water potential to an area of lower water potential, until a dynamic equilibrium is established
What is water potential?
pressure created by water molecules
What are the units for water potential?
kPa
What is the water potential of pure water at 25°C and 100kPa?
0
What 3 conditions are required for water potential to = 0
pure water
25°C
100kPa
What happens to water potential if there is more solute?
water potential becomes more negative
When does water potential become more negative?
when there is more solute
What is the equation for volume of stock solution?
require concentration x final volume needed
________________________
concentration of stock solution
What is the equation for volume of distilled water?
final volume needed - volume of stock solution
What happens to plants when osmosis into cells occurs?
protoplast swells so cell becomes turgid
What happens to animals when osmosis into cells occurs?
lysis of cells
What happens to plants when osmosis out of cells occurs?
protoplast shrinks so cell becomes flaccid
What happens to animals when osmosis out of cells occurs?
crenation of cells
What is meant by a passive process?
process which requires no energy from ATP hydrolysis
What is meant by simple diffusion?
net movement of small, lipid-soluble molecules directly through the bilayer from an are of high concentration to an area of lower concentration, down a concentration gradient
What type of process is simple diffusion?
passive process
What is meant by facilitated diffusion?
specific channel or carrier proteins with complementary binding sites transport large and/or polar molecules/ions that are no soluble in the hydrophobic phospholipid tail, down a concentration gradient
What type of process is facilitated diffusion?
passive process
What 2 types of diffusion are passive processes?
simple diffusion
facilitated diffusion
How do channel proteins work?
hydrophilic channels bind to specific ions, causing one side of the protein to close and the other to open
How do carrier proteins work?
binds to complementary molecule causing conformational change which releases molecule on other side of membrane
Why is active transport not a passive process?
requires energy from ATP
What are 5 factors affecting diffusion rate?
1) temperature
2) diffusion distance
3) surface area
4) size of molecule
5) difference in concentration
What are 2 cell adaptations which max rate of transport across membranes?
- many carrier/channel proteins
- folded membrane to increase SA
What is meant by active transport?
ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape so specific carrier proteins transport molecules/ions from area of low concentration to area of high concentration, against a concentration gradient
What is the shape of a graph for simple diffusion?
straight diagonal line where rate of diffusion increases proportionally as concentration increases
What is on the x and y axis of a graph showing simple or facilitated diffusion?
x-axis = concentration
y-axis = rate
What is the shape of a graph for facilitated diffusion?
straight diagonal line that later levels off when all channel/carrier proteins are saturated
What is one similarity between active transport and facilitated diffusion?
both may involve carrier proteins
What are 2 differences between active transport and facilitated diffusion?
- facilitated diffusion may also involve channel proteins
- active transport requires energy from ATP hydrolysis whereas facilitated diffusion is a passive process
What is meant by co-transport?
movement of a substance against its concentration gradient is coupled with the movement of another substance down its concentration/electrochemical gradient
What are 2 types of intrinsic protein?
symport
antiport
How do symport intrinsic proteins work?
transport substances in same direction
How do antiport intrinsic proteins work?
transports substances in opposite direction
What is an example of antiport intrinsic proteins at work?
sodium-potassium pump
What happens to substances in co-transport?
bind to complementary intrinsic proteins
What are 3 ways co-transport is involved in absorption of glucose/amino acids in the small intestine?
- sodium ions are actively transported out of epithelial cells and into the bloodstream
- sodium ion concentration is lower in epithelial cells than in the lumen of the gut
- transport of glucose/amino acids from lumen to epithelial cells is coupled to facilitated diffusion of sodium ions down electrochemical gradient
