Biological Membranes Flashcards
Definition of a complex lipid
A lipid with multiple parts
Purpose of a head group
To allow amphipathic capacity
Definition of amphipathic
A molecule having both hydrophobic and hydrophillic parts
Basic structure of sphingolipids
A sphingosine (long chain alcohol), a fatty acid (attaching via acyl group), and a polar head group
X group of ceramide
None
X group of sphingomyelin
phospho-choline
X group of lactosyl-ceramide
> 1 saccharide
X group of neutral glycolipid
Glucose
X group of ganglioside
Complex saccharide, including various types of branching
Cholesterol size, typology, building blocks, place of biosynthesis
27 carbons, planar typology (can be stacked), built from carbon units of acetyl-CoA, synthesized by all cells (mainly the liver) in the cytosol
How are micelles formed
By fats and detergents; the head group is larger, so the chemicals wrap around to form balls easily. Only a single fatty acid tail.
How are liposomes formed
By phospholipids; the two fatty acid tails cause no difference between the head group and the tail group, so the curvature is slight and a bilayer is formed.
Issues with early view of biomembranes
1) Didn’t consider heterogenity of components, as each layer may be made up of different components
2) Didn’t consider heterogenity of protein insertion, as each layer may have different proteins
3) Leaflet asymmetry (leaflets being glycolipids, oligosaccharides, etc.)
4) Motional restrictions inherent in the layer (not just fluid)
5) Interaction with the cytoskeleton
Most abundant biological lipid
Cholesterol, ~20%
Relative concentration of sphingomyelin and phosphatidylcholine
50/50
Phosphatidylserine composition and role
Nearly 10%, relatively high, used for signalling
Are lipids glycosylated
Yes, extensively
Why membranes are asymmetric (why are the two membranes comprising the bilayer different?)
Facilitates association / integration of membrane proteins, provides membrane curvature, and provides correct localization of signalling molecules
Name three kinds of enzymes that mediate membrane asymmetry
Flippases, floppases and scramblases
Main phospholipids on outside surface of membrane in erythrocytes
Phosphatidylcholine and sphingomyelin
Main phospholipids on inside of membrane in erythrocytes
Phosphatidylethanolamine and phosphatidylserine
Term for ‘ lipid rafts’ on membrane
Mini-domains
Main composition of mini-domains
Cholesterol and sphingolipids with long acyl lengths
Phase of lipids in mini-domains
Ordered; becomes more rigid.
Size and timespan of mini-domains
10-300nm, short-lived
Protein composition of mini-domains
Caveolae proteins, theoretically for a structural role, GPI-anchored proteins
Advantage rafts have with proteins
Localizing proteins for related processes can help accomplish that process, such as for signalling
Name four ways to aggregate proteins for lipid rafts
(1) Protein-protein coupling
(2) Protein-lipid coupling
(3) Extracellular matrix
(4) Cytoskeleton
What aggregation does to proteins
Affects motion and localization of the proteins
Types of lateral movement in proteins
(1) Transient confinement by obstacle clusters
(2) Transient confined by the cytoskeleton, which acts like a fence
(3) Directed motion by attachment to the cytoskeleton
(4) Free and random diffusion in the membrane plane
Which phospholipid, out of sphingosine, sphingomyelin, neutral glycolipids, lactosyl-ceramide, ceramide and ganglioside has a fatty acid (amide) residue?
All except sphingosine.
Which phospholipid, out of sphingosine, sphingomyelin, neutral glycolipids, lactosyl-ceramide, ceramide and ganglioside, has a polar X group?
All except sphingosine and ceramide.
