Lectures 1-6 (membrane structure & function) Flashcards
What are the equations for Ohm’s law?
Current (I) = Volts (V) / Resistance (R)
Current (I) = Volts (V) x Conductance (G)
What is Conductance?
G
1/Resistance
What is the Nernst equation?
cant write here
What do each part of the Nernst equation stand for?
R F T z
R - Gas constant 8.314 V C K-1 mol-1
F - Faraday’s constant 9.648x104 C mol-1
T - Absolute Temperature (°K) 273.0°K at 0°C
z - Ion valency (charge) ±1,2,3…
what happens when [Ion]o = [Ion]i
Eion = o
because x ln1 = o
what happens when [Ion]o > [Ion]i
= > 0 if z is +ve
=
what happens when [Ion]o
= if z is -ve
what do all cells do/have?
have a membrane potential and express ion channels
what are integral and peripheral proteins?
integral embedded in the membrane.
peripheral one side or the other.
Describe the Fluid Mosiac Model of the lipid bilayer.
Singer and Nicholson 1972.
Emphasizes fluidity, simplicity.
lipid bilayer as a consequence of a series of random electrostatic forces, causes them to line up.
There are some proteins floating around, don’t touch anything.
What replaced the Fluid Mosaic Model?
the evolved Fluid mosaic model emphasises order.
“the picture of a membrane as a lipid sea in which proteins float freely is greatly oversimplified”…
what are saturated/unsaturated lipids?
saturated - no double bonds
unsaturated - 1-6 double bonds
Long chains = less fluid
Cis/trans unsaturated bonds?
Cis kinked.
Double cis bonds make membranes fluid (kinks stop lipids packing closely together)
Trans found in processed foods, increased cholesterol.
describe the types of membrane lipids.
PHOSPHOLIPIDS, all have a glycerol backbone.
Phosphatidylethanolamine, Phosphatidylinositol, Phosphatidylserine (if on outside signals phagocytosis) and Phosphatidylcholine.
GLYCOLIPIDS
Galactocerebrosides and Gangliosides
CHOLESTEROL
how are lipids distributed?
asymmetrically, generated by lipid flippase ATPase pumps.
Move lipids from one leaflet to the other leaflet?
What happens if there is a loss of symmetry?
inhibition of flippases and activation of scramblases.
PS presented on the outside of the cell, signalls macrophages to start phagocytosis/apoptosis.
what is the role of phospholipids?
structure signalling (PI)
what is the role of cholestrol?
maintaining stability.
decreasing permeability.
what is the role of glycolipids?
cell recognition.
protection, additional layer on outside of cell.
can influence electrical properties of the cell.
describe the ratio/contribution of lipids and proteins.
50 lipids : 1 protein
but proteins contribute 30-45% mass since much larger.
what is a GPI anchor?
anchors protein in the outer leaflet of PM.
Specific phospholipase may release this protein from the cell as a signal pathway.
Describe the structure of transmembrane protein structures
Polar protein regions:
- Prefer polar environment
(H2O + lipid headgroups)
- Loathe lipid interior
Non-polar regions:
- Prefer non-polar (bilayer)
- Loathe H2O + lipid heads
describe membrane synthesis.
Membrane lipids synthesised in ER, then “randomly” incorporated into ER membrane.
Lipids trafficked in membrane vesicles which fuse in to plasma membrane.
Lipid asymmetry established by flippases.
Membrane proteins are synthesised at RER and trafficked to the plasma membrane.
what is SRP?
signal recognition particle..
translocator allows the protein to work through the membrane and come through the other side.
For secreted protein, once protein has gone through translocator,
SRP can be cleaved and you get a free floating soluble protein.