Membranes 1

Question 1

role as a barrier

Answer 1

prevents loss of required metabolites

Prevents entry of unwanted material

Question 2

Other functions

Answer 2

capacitor: stores energy
Important for energy production and electrical signalling
Receives info, has a transduction signal within the cell
selective permeability
Maintain ionic comp: ion channels and transporters
Maintain cytoplasmic pH, osmotic pressure (aquaporins)
Sense environment- receptors
Anchor cytoskeletal structures
Mediate cell-cell and cell-ecm interactions
Carry out membrane requiring enzymatic reactions

Question 3

What does it mean to say phospholipids are ampipathic

Answer 3

have hydrophilic head and hydrophobic tail

Question 4

Bilayer

Answer 4

Lipids arrange so hydrophobic parts not in contact with water, and hydrophilic parts are
Energetically favourable to form sealed environment-bilayer joins at ends so edges are not exposed to water

Question 5

glycerophospholipids

Answer 5

AKA phosphoglycerides
Based on 3C glycerol
2 fatty acid tails ester linked to -OH group of glycerol, and one -OH linked to phosphate
X (polar head group) attached to phosphate can be different
Different head groups give particular properties
Negative phosphate and OH positive groups on the head interact with water

Question 6

X= choline

Answer 6

phosphotidylcholine

Question 7

phosphotidyl

Answer 7

fatty acid part of glycerophospholipids

Question 8

Glycolipids (sugar attached)

Answer 8

Sphingolipids

Question 9

Sterols

Answer 9

cholesterol

Question 10

phospholipids

Answer 10

glycerophospholipids, sphingolipids

Question 11

When are lipids not phospholipids

Answer 11

don’t have phosphate eg some sphingolipids don’t have a phosphate

Question 12

cholesterol

Answer 12

very small polar head group (OH)- rest of molecule is hydrophobic, and doesn’t have a phosphate- not PP
Although almost entirely HC, is amphiathic because OH interacts with water.
Absent from prokaryotic and plant cells

Question 13

How are lipid bilayers fluid

Answer 13

PPs rotate freely, diffuse laterally and can move in flip flop motion from one leaflet to another

Question 14

Flip flop- energy

Answer 14

less energetically favourable, as energy cost for moving hydrophilic/polar head group through hydrophobic environment- likely energy driven

Question 15

Why is membrane fluidity important

Answer 15

Compromise between rigid, ordered structure and non viscous liquid
Allows for interactions in the membrane eg membrane proteins can assemble

Question 16

Experiment for demonstration of membrane fluidity

Answer 16

Fuse mouse and human cell, different colours for membrane proteins- labels
Afetr incubating at 37 degrees for 40 mins, membrane proteins mix

Question 17

Factors influencing membrane fluidity

Answer 17

1. temp- more motion so membrane more fluid
2. Saturation of fatty acid chains- kink in chain due to double bond means chains can’t pack as closely hence more fluid
3. Length of acyl/FA chains
4. cholesterol- decr fluidity. Rigid ring structure aids packing of lipids

Question 18

Lipid asymmetry

Answer 18

Different composition in each leaflet
Some lipids ony found in cytoplasmic facing one, others eg glycolipids only found on etracellular leaflet
Cholesterol even across both

Question 19

Eukary vs prokary lipid diversity

Answer 19

Eukary diversity greater

Question 20

When in water PPs aggregate into

Answer 20

spherical micelles and liposomes, or bilayers

Question 21

Type of structure aggregate into determined by

Answer 21

Length of FA chains, saturation and temp

Question 22

Micelles rarely formed because

Answer 22

FA chains too bulky to fit

Question 23

Sphingolipids

Answer 23

Derived from sphingosine, and contains a long chain FA attached in amide linkage to sphingosine amino group
Some sphingolipids have phosphate based polar head group, some are amphipathic glycolipids, whose polar head groups are sugars and not linked via a phosphate group