Cell membranes 2 Flashcards
(22 cards)
Why is membrane fluidity important?
Membrane protein diffusion in signalling
Distribution of lipids and proteins in daughter cells
Membrane fusion (e.g. molecular trafficking)
Allows membrane lipids and proteins to become distributed after delivery to the membrane
How do B cells activate?
B cells activate by allowing B cell receptors (BCRs) to cluster at the plasma membrane.
What movement do proteins and lipids have in the fluid mosaic model(FMM)?
Lateral and rotational movement.
Flip-flop rare.
How did the FMM get its name?
Membrane is a mosaic of protein molecules embedded in a fluid lipid bilayer
History of development for FMM…
1895- lipids on cell surface(overton)
1917- Phospholipid on monolayer
1925- Cell membranes are phospholipid bilayer
1935- lipid bilayer plus protein sheets
1960- sandwich model
1972- FMM(singer, nicolson)
How are membrane molecules held in place?
Weak hydrophobic interactions.
Most lipids and some proteins can drift laterally in the plane of the membrane(2D fluid behaviour)
How is the lateral mobility of plasma proteins restricted?
Tethered through actin to the cortical cytoskeleton.
Tethered to ECM molecules(integren binding)
Tethered to proteins on another cell,e.g antigen.
Diffusion barriers,e.g gut.
Ezrin is activated by _______________.
phosphorylation
Activated ezrin can bind couple ____________proteins to ______ filaments
transmembrane
actin
What are the different lipid components categorised into?
Functionalised microdomains.
LIPID RAFTS
They play important signalling roles.
Give the structure and function of lipid rafts.
Are enriched in sphingolipid and sterol (cholesterol) .
Selectively recruit different membrane proteins, such as GPI-anchored proteins.
What was the expansion in research post 1972 on the FMM?
Membrane-associated cytoskeletal assemblies
ECM interactions
Specialised lipid-protein domains
More concentrated with membrane proteins
Give 2 out of the 3 alternative models for the FMM.
‘Lipid raft model’
‘Protein island model’
What does FRAP stand for
FRAP = fluorescence recovery after photobleaching
t1/2 = halftime to recovery
How do you measure membrane fluidity?
Fluorescently labeled membrane proteins
⬇
Bleach patch with laser beam
⬇
Labeled proteins diffuse randomly throughout membrane
⬇
Fluorescence returned to bleached patch.
What are the two types of SLP’s
DOPC
DPPC
Describe the features of DOPC
Unsaturated, kinks in hydrophilic tails.
Low viscosity
Describe the features of DPPC.
Saturated C-C bonds all.
High viscosity.
Define viscosity.
Viscosity is a measure of a fluid’s resistance to flow.
What are the limitations of FRAP?
Can’t track individual proteins as often there are large numbers of proteins crossing a large area of membrane.
What is the alternative to FRAP?
SPT(single particle tracking)
Describe SPT(single particle tracking)
Fluorescent proteins
Organic dyes
Labelled antibodies
Antibody-coated gold nanoparticles
