Week 3 MPW Lecture 4 Flashcards
How does the composition of membrane changes when going from the inside of the cell to the outside?
The cholesterol levels increase as you go towards out of the cell, and the phosphoglycerides decrease, meaning outside membrane is more rigid.
Why are the membranes two leaflets being asymmetric?
a) What about the proteins?
i) Transmembrane
ii) GPI-anchored
iii) Lipids-anchored
Different lipids are distributed differently on the leaflets of the membrane.
a) Both
b) Outside
c) Inside
How are lipids flipped between bilayer leaflets?
Uses a flippase which uses ATP
Why does the lipid composition varies across the membrane?
To encourage phase separation, which creates different regions within the membrane
What are membrane rafts (lipid rafts)?
A more rigid region in the membrane which is rich in cholesterol and sphingolipids (more gel)
What are the uses of membrane rafts?
Important for altering the location of membrane proteins;
a) Bringing signalling systems together
b) Organising the start of endocytosis
c) T cell activation
d) Bring together proteins, or keep them away from each other; can be moved in and out of membrane rafts
How are membrane rafts observed?
Using an Atomic Force Microscopy;
a) A piezoelectric scanner is under the sample moves which moves the sample
b) A cantilever arm is used to sense the level of the sample
c) A laser is shown on the cantilever arm and the reflection is detected
How are membrane rafts useful for signalling?
For signalling to occur a dimersiation cascade need to happen, the proteins need to be close together
What is a GPI anchor?
A protein that is anchored to the cell membrane
What are the main differences between the fluid mosaic model and the membrane raft model?
In the membrane rafts there are
a) Different regions with different thickness
b) Different rigidities
c) Can have different lipid compositions
What is tapping mode in Atomic force microscopy?
A blunter needle and faster tapping
