Membranes & Proteins Flashcards
Function of membranes
- functional barrier
- energy source
- organise & regulate enzyme activity
- facilitate signal transduction
- supply substrates for biosynthesis
- protein recruitment platform
What do membranes consist of
- lipids
- proteins
What are the three types of membrane lipids
- glyceropphospholipids (phospholipids)
- sphingolipids –> glucoshpingolipids (glycolipids)
- sterols
What are fatty acid chains
- long aliphatic carbon chains
- terminal carboxylic acid
How does hydrophobic affect water molecules
Reorganise
What happens if hydrophobic molecules cluster together
- smaller no. of water molecules affected —> lower energy cost
What could lipids form
- bilayers
- micelles
How are fatty acids named
XX:Y n-y
XX: C atoms
Y: =s
n-y: position of 1st double bond (starting at methyl terminus)
Describe saturated lipids
- no =
- straight
Describe unsaturated lipids
- contains =
- cis = —> 30 degrees kink
- trans = —> no effect
What does diff. in length and saturation of fatty acids influence
How phospholipids pack against one another
Where does chemical diversity in glycerophospholipids arise from
- combination of two fatty acids
- sn-1 position linkage
- head group linkage
Describe sn-1 fatty acid (in glycerophospholipids)
- saturated
- monounsaturated
Describe sn-2 fatty acid (in glycerophospholipids)
- more monounsaturated
- polyunsaturated
What are the anaionic phospholipids
- PS
- PI
- PG
- CL
What is the charge of zwitterionic phospholipids
Zero
What do PS & PE glycerophospholipids contain and what does that help towards
Reactive amines
H-bonds
Which glycerophospholipids are bulky and what does that help with
- PI, PC & CL
- their packing
What lipids are found in mitochondria
PG & cardiolipins
How are PIPs generated
Head group phosphorylation at positions 3, 4 & 5 of phosphatidylinositol
How many different PIP species are there
7
How saturated are the tails of PIP
Saturated
Polyunsaturated
What is the most abundant PIP in mammalian plasma membrane, where is it found
PI(4,5)P2
Inner leaflet of plasma membrane
What does PTEN protein do
Convert PI(3,4,5)P3 to PI(4,5)P2
What do sphingolipids consist of
- sphingolipids base
- N-acyl chain
- head group
What is the most common sphingolipid
Sphingomyelin (SM)
What head group does sphingomyelin have
PC
The amide gp on sphingolipids have the ability to h bond, what does that help with
Interactions of sphingolipids with cholesterol and polar parts of proteins
Describe N-acyl chain in sphingolipids
- more saturated
- longer than acyl chains of glycerophospholipids
What are the different head groups of glycosphingolipids
Oligosaccharides
sugar building blocks
Where are glycosphingolipids found
Outer leaflet of membrane, 5% of membrane
Which groups are exposed to cell surface in glycosphigolipids
- sugar
- help with cell-cell adhesion
- membranes act as recognition sites
Name 3 components of glycolipids
Ganglioside GM1, 2, 3
Where do h bonds form in glycolipids
Between sugars and lipids tail
What is self-aggregation of GM1 driven by
Sugars
What groups do sterol have
- hydroxyl group
- hydrocarbon tail
What is the most common sterol in animals
Cholesterol
What sterols is found in yeast & fungi membrane
Ergosterol
What sterols are found in plants
- sitosterol
- stigmasterol
What can cholesterol shape allow it to do
Align better with saturated site chains
Cholesterol interaction with POPC
OH group is not buries in complex
Describe interaction between cholesterol and sphingomyelin
- H bond: OH of cholesterol & NH of sphingolipid
- OH of cholesterol masked by polar head of sphingomyelin
What are the three different membrane curvatures
- cylindrical (flat membrane)
- conical (negative membrane)
- inverted-conical (positive membrane)
What lipids are cylindrical
- PC
- PS
What lipids are conical
- PE
- PA
What lipids are inverted-conical
- lysosome-GPLs
- phosphoinositides
What does -ve curvature of PE lead to
- generation of non-bilayer
- eg fusion
What are the types of lipid diversity
- chemical/structural
- compositional
Describe the lipid asymmetry in erythrocytes membranes
- 50% cholesterol
- high conc. of PC & SM in outer leaflet
- high conc. of PS & PE in inner leaflet
Give an example of functional importance of lipid asymmetry in cell signalling
- PS translocate to extra cellular layer when cell dies
- signals neighbouring cells, macrophages
- phagocytise dead cell
How does movement of PS occur
Via scramblases
What direction are secondary signalling messengers oriented towards
Interior of cell
When does lipid interdigitation occur & what does it do
- Lipid length asymmetry in membranes
- Coupled two leaflets together
What are the directions of lipid movement
- rotational
- lateral
- transverse
What is rotational movement
- spinning of lipids around axis
- doesn’t alter positions
- affects interactions with neighbouring molecules
What is lateral movements
- neighbouring lipids exchange places
- lipids change position within bilayer
What is transverse movement
- exchange of molecules between leaflets
- lipids move across bilayer by transverse diffusion or proteins
What is the difference between lipids composition of tumour tissues (lung cancer) and normal tissues
- PI higher in tumour
- SM lower in tumour
What is different about lipid composition in tumour tissues in breast cancer
PI, PE, PC and SM sig. higher in tumour
Which lipid is increased in type ii diabetes, Alzheimer’s and CF
Ceramide
What lipids are increased in outer leaflet of thalassaemic and diabetic red cells
- PS
- PE
What phases are covered by lamellar phase
- lamellar liquid crystalline (liquid disorder)
- solid gel
- liquid-ordered
What does the adopted phase depend on
Lipid structure
What are lipid droplets
- storage organelles
- maintain lipid
- maintain energy homeostasis
What are hydrophobic cores of neutral lipids enclosed by (droplets)
Phospholipid monolayer
- has specific proteins
Where do lipid droplets originate from
- ER
When are lipid droplets initiated
Neutral lipids are produced
What do neutral lipids result from
- esterification of a fatty acid to triacylglycerol or sterol to sterol ester
Where are neutral lipids dispersed at low concs.
Between leaflets of ER bilayer
What can impairment of fatty acid storage in lipid droplet result in
- type 2 diabetes
- non-alcoholic fatty liver disease
Describe spontaneous transverse movement
- bidirectional
- no energy
- non-specific
describe P-type flippase transverse movement
- inward movement
- ATP
- specific
Describe ABC flippase transverse movement
- outward
- ATP
- specific
Describe scramblase transverse movement
- bidirectional
- no energy
- non-specific
- Ca2+ dependent
