W2 Membrane I

Question 1

Membrane lipids

Answer 1

Hydrophilic phosphate head facing outwards + hydrophobic fatty acid tail facing inwards = PL bilayers
Non-covalent assemblies
Movement w/in membrane = flexible
Amphiphatic = molecule that possesses both hydrophobic and hydrophilic elements
Only small OH group in CL exposed to intra/extra cellular
Glycoprotein = cell recognition, stability
SM = PL where glycerol backbone replaced by sphingosine (amino alcohol w/long unsaturated hydrocarbon chain)
PE + PL = intracellular signalling
PL bilayer arranged in a structure where energetically favourable

Question 2

Membrane fluidity

Answer 2

Temperature - increase KE, fatty acid tails of PL become less rigid + allow more movement of proteins + other molecules in/out membrane
Fatty acid composition
Chain length = increase in length means an increase in rigidity as there are increased interactions
Degree and extent of saturation = saturated fatty acyl chains increase rigidity if mixed w/unsaturated the chains can not pack together
Cholesterol content = CL OH group forms H bonds w/PL so the hydrophobic tail disrupts the regular interaction b/een fatty acyl chains
Lateral movement of lipids in the membrane is rapid

Question 3

Transverse movement in CM

Answer 3

Slow + requires 3 enzymes
Floppase = moves PL from inner to outer leaflet
Flippase = moves PL from outer to inner leaflet
(Both require ATP)
Scrambalase = bidirectional movement
Only on cytosol side so cytosolic enlarged

Question 4

Cholestrol + temp

Answer 4

Inc temp = move apart
Low temp CL – increase fluidity w/out making membrane itself too rigid, intercalates b/een PL + prevents from clustering together and stiffening
High temp CL – reduces fluidity as stabilises membrane + raised MP

Question 5

Spur cell anemia(end stage of liver disease)

Answer 5

Less able to function as RBC = increase of CL w/in membrane so decrease in membrane fluidity

Question 6

Apoptosis

Answer 6

Programmed cell death
P – inner surface
When on outer = signal for apoptosis for PC
Tissues regenerating themselves w/out causing inflammation

Question 7

Fluid mosaic

Answer 7

Fluid = parts of membrane move around freely (if not attached to other parts of cell)
Mosaic = patchwork of proteins found in PL bilayer

Question 8

Integral membrane proteins

Answer 8

Single or multi pass (as in crossing the plasma membrane)
Strong non-covalent bonds
Transmembrane (spans entirety of CM + permanently attached) domain often an α-helix
Can be predicted (if membrane bound) from AA sequence
Tightly associated w/membrane + interact extensively w/lipid bilayer
AA will be hydrophobic
Hydrophilic in core but mostly in extracellular

Question 9

Peripheral membrane proteins

Answer 9

Located on the extracellular or cytosolic membrane
Associated by non-covalent bonds
More weakly associated
Some transly
Peripheral proteins interact with integral proteins or lipid polar head groups

Question 10

Lipid anchored membrane proteins

Answer 10

Covalently linked to a lipid molecule such as glycerol-phosphatidylinositol. Can contribute to the function of the protein to which it is attached. Can play an important role in increasing molecular hydrophobicity. This allows for the interaction of proteins with cellular membranes and protein domains

Question 11

Membrane carbohydrates

Answer 11

Carbohydrates are associated with both membrane lipids and proteins
Form 2-10% of the membrane weight
Carbohydrate on all membranes faces away from the cytosol
They are often involved in cell-cell interactions or cellular recognition
In RBCs 8% of the weight is carbohydrate
Blood group due to carbohydrates attached to lipids