What are the main functions of a lipid bilayer?
- Highly selective permeable barrier
- Communication
- Control a chemically closed environment
- Allow recognition of cells
What is the basic structure of a phospholipid?
-Glycerol backbone with 2 FA tails and a phosphate head group (head group can be choline,a’a, amine etc, FA often 16-18C long)
What is a sphingomyelin?
-Phospolipid with glycolipid moiety instead of phosphate
Explain why phospholipids form micelles
-FA tails are hydrophobic whilst phosphate heads and hydrophilic. Tails attrext each other forming a non-polar moiety which repels water whist heads attract each other anr attract water.
Describe the directional movement which phospholipids can do
- Flexion of FA tails
- Rotation
- Lateral diffusion
- Flip Flop
What is the function of cholesterol within cell membranes?
-Cholesterol helps stabilise the membrane by reducing packing and movement
What is SDS-PAGE?
-Denaturing proteins with detergent and then using polyacrylamide Gel Electropheresis to separate proteins by size
How do proteins move in membranes and what restricts this movement?
- Confomational change
- Rotational
- Lateral diffusion
- Aggregation, tethering to membrane and interactions with other cells limits movement
What are peripheral and integral proteins in pm?
- Peripheral proteins are those which are bound to the surface of membrane by electrostatic or hydrogen bonds. They can be removed by changes in pH eg spectric
- Integral proteins are those which span the membrane and interact with the hydrophobic moiety. They cannot be removed by pH change. eg band 3 on RBC
Name 2 haemolytic anaemias which are caused by diseases of the cytoskeleton of RBCs
- Hereditary spherocytosis
- Hereditary elliptocytosis
What type of transport are ligand-gated and voltage gated ion channels?
-Facilitated diffusion
State the common electrolyte concentrations of intra and extracellular fluid
- Na = 145mM EC, 12 mM IC
- K = 4mM EC, 155mM IC
- Cl= 123mM EC, 4mM IC
- Ca = 1.5mM EC, 0.1uM IC
Why is NCX/NHE classed as secondary active transport?
-Uses the Na gradient produced by NaKATPase to exchange 3Na for 1 Ca/H thus uses ATP indirectly
How is SGLT a secondary active transporter?
-Uses Na gradient from NaKATPase to transport glucose against its concentration gradient
What is the defect in CF?
-Point mutation causing CFTR to be defective. It is a chloride ion meaning chloride cannot leave cells. Causes H2O to remain in the cell thus the mucus is viscous and sticky
Which ion transporters are responsible for controlling intracellular calcium? Say a little about each
- PMCA -> high affinity low capacity ie residual calcium. Directly uses ATP. Ca out for H in
- NCX -> Low affinity high capacity ie high calcium. Uses Na gradient. 3Na in for 1 Ca out ie after depolarisation. Reversed during depolarisation
- SERCA -> High affinity low capacity ie residual calcium. Directly uses ATP. Ca out for H in
- Mitochondrial uniporter -> low affinity high capacity
Describe how ion transporter contribute to control of cellular pH. What else are these channels involved in?
- Acid extruders = NHE and Na Bicarb transporter (Na and HCO3 in for H and Cl out) decrease the pH of a cell
- Base extruders = Anion exchangers (HCO3 out for Cl in) increase the pH of a cell
- Regulating cell volume too
Explain how the RMP of a cell is set up. Why isnt it equal to Ek
- RMP determined by the ion selectivity of the channels a cell possesses as well as whether these channels are open or closed.
- Most cells open K+ channels dominate the membrane ionic permeability at rest allowing K + to flow out of the cell, this generates a chemical gradient. K leaving generates a negative charge relative to the outside. This attracts the +ve K back into the cell and is known as the electrical gradient. When the electrical and chemical gradients are equal and opposite the cell has reached equilibrium and that will be its RMP.
- However ion channels not 100% effective and flicker open occasionally allowing leaking of cells in/out. This decreases RMP a little so RMP is not equal to Ek
State the average RMP for Nerve, cardiac, smooth and skeletal muscle cells
- Nerve = -70mV
- Cardiac = -80mV
- Skeletal muscle = -90mV
- Smooth = -50mV
Broadly, Which receptor types are responsible for fast and slow synaptic transmission?
- Fast is receptors directly bound to ion channels ie ligand-gated ion channels -> generates excitatory posy synaptic potentials (or inhibitory PSP if leads to hyperpolarisation eg GABA)
- Slow is receptors bound to GPCRs which bring about a response using a second messenger
