2.5.5 factors affecting membrane structure & permeability

Question 1

what happens to membrane structure & permeability when temperature decreases

Answer 1

• saturated fatty acids become compressed
• membrane fluidity maintained = unsaturated fatty acids become compressed & the kinks in their tails push adjacent phospholipid molecules away
• cholesterol buffers effect, to prevent reduction in membranes fluidity
  –> prevents phospholipid molecules from packing together to closely, as cholesterol molecules in between groups of these molecules

Question 2

what determines the membranes fluidity at cold temperatures

Answer 2

proportions of saturated & unsaturated fatty acids within cell surface membrane

Question 3

what happens to membrane structure & permeability when temperature increases

Answer 3

• phospholipids acquire more kinetic energy & move more = increases fluidity
• permeability increases
• affects position & function of membrane-embedded proteins
• increase in membrane fluidity = change ability of cells to signal by releasing chemicals (often by exocytosis)
• cholesterol molecules act as buffers (to some extent) to effects of increasing heat as reduce increase in membrane fluidity

Question 4

effect of high temperature of proteins (within the membrane)

Answer 4

• causes atoms within their large molecules to vibrate & breaks down hydrogen/ionic bonds which hold their structure together = they unfold
• tertiary structure changes & cannot change back when cooled = denatured
• cytoskeleton threads (underneath membrane) & membrane-embedded proteins denature = plasma membrane begins to fall apart & more permeable due to holes
• membrane-embedded enzymes will become denatured as shape of active site changes or they move = rate of reactions they catalyse slow down

Question 5

which solvents may damage phospholipid membranes

Answer 5

organic solvents (eg. acetone & ethanol) as they dissolve lipids