Biomembranes and ECM Flashcards
Characteristics of biomembranes
- Permeable to..?
- When broken..?
- Symmetric or asymmetric wrt to what?
- % content?
- Permeable to hydrophobic substances, impermeable to hydrophilic substances
- When broken, spontaneously reseal
- Asymmetrics wrt proteins and lipids
- 50% lipid content
Biomembranes are composed of ______ including ____ (3)
Several broad classes of lipids including (1) phospholipids (2) cholesterol (3) glycolipids
4 basic types of phospholipids + 3 extra
Distribution?
(1) Phosphatidylserine (when translocates to outer leaflet –> apoptosis) (2) phophatidylethanolamine (inner leaflet) (3) phosphatidylcholine (outer leaflet) (4) sphingomyelin (found in myelin, can be broken down into phosphocholine + ceramide, major targets for pore-opening toxins and viruses, outer leaflet)
(1) Cardiolipin = mitochondrial membrane specific phospholipid
(2) Sphingosine
(3) Glycolipids = glycosylated sphingosine molecules
Lipids are NOT distributed equally on both leaflets of membrane
Cholesterol
- Found?
- Associates with, and effect of? Preferentially associates with?
- Found in both inner and outer leaflets of membrane
- Associates with both saturated (make membrane more fluid) and unsaturated (stiffens membrane) phospholipids.
- Preferentially associates near saturated regions, especially tails of sphingomyelin
Membrane microdomains: (2) types
Are regions that tend to be wider and where certain proteins are found.
- Membrane rafts: have higher density of cholesterol and sphingomyelin
- Caveola: are invagination of cell membranes formed by caveolin
Lipid translocators (3)
(1) Flippase = ATPase that moves PE/PS from outer to inner leaflet
(2) Floppase = ABC that moves phospholipids from inner to outer leaflet
(3) Scramblase = moves lipids towards equilibrium; NO ATP USE (they are more active when intracellular Ca2+ levels increase)
Main intracellular lipid linkers classes (3)
- Important in signaling
(1) Palmitoyl (C-link; anchor proteins on cytosolic side where important signaling occurs)
(2) Myristoyl (C-link)
(3) Farneysl (S-link)
GPI anchors
Help attach extramembrane proteins to outer leaflet
Extracellular matrix is ___. If more organized, it is called ___.
Stuff between cells. Basal lamina.
What do laminins interact with and what are they important for?
They interact with integrins and dystroglycans. They are important for immune cell migration.
What are proteoglycans and what is their role? E.g.?
Proteoglycans are heavily glycosylated low affinity binders in the ECM. E.g. heparin
What are glycosaminoglycans (GAGs) and what are their roles?
GAGs are proteoglycans with multiple unbranched disaccharides that are negatively charged. They increase viscosity of the ECM.
What is fibronectin and what does it do?
Fibronectin binds collagen, integrin, and heparin. It connects matrix proteins to membrane integrins.
What is the major type of collagen in the ECM and what does it do? Associated disorder?
Type IV. It makes a meshwork (not long fibrils). It is affected in connective tissue disorders.
Alport syndrome
Mutations in Type IV collagen leads to poor glomerular filtration leading to blood and protein in urine. It is an XL disease due to a missense mutation.
