Lecture 1: Membranes Flashcards
What is Lecithin?
Amphiphilic
Phosphatidylcholibe is common in biological membrane
Named by polar head group
Variety of hydrophobic tails
Tails are Saturated or unsaturated fatty acids
What is sphingolipids?
Use sphingosine and fatty acid for hydrophobic side chains
What is cholesterol?
Sterol Required for membrane structure and flexibility Comprises about 30% of the membrane Essential for life We make it Associated with phospholipids Controls fluidity of membrane
What is integral membrane protein?
Integral monotopic protein
Singlepass protein
Multipass protein
Multi-subunit protein (ion channels form)
What is lipid-anchored membrane proteins?
Fatty acid
Isoprenyl anchor
GPI anchor
If membrane was lipid, what would they be?
Insulators
Not be able to pass molecules that are charged
What are lipid rafts?
Membrane is not uniform Arranged in microdomains Have more cholesterol Membrane is thicker Generates a wider membrane than average Behaviour depends on lipid environment
What is phospholipid bilayer poorly permeable to?
Water and ions
Despite phospholipid bilayer being poorly permeable to water and ions, how can they pass these?
Water channels
Ion transporters
Hydrated ion selective Chanel
What happens at equilibrium?
Equal number of ions move back and forth to maintain the equilibrium
What perturbs ion distribution?
Presence of impermeant anion
Why is the presence of osmotically active and impermeant anions an issue?
Affect H20 balance
How do you neutralise the negative charges within the cell?
Actions flow in
Increases the osmotic pressure inside relative to the outside of cell
What does increased osmotic pressure force?
Water to flow into the cell
Tissue swelling
How do you even the osmotic forces?
Make Na+ ions effectively impermeant
What is transmembrane Na+ gradient used for?
Signalling
What is metabolic energy?
Sodium-potassium ATPase
What is the equilibrium state?
Equal movements of potassium down the concentration gradient and in reverse down the electrochemical gradient
When these are equal and opposite and there is no further charge movement
What do Na+ ions respond to?
Applied depolarisation
How is applied depolarisation transduced?
Channel
The channel has charged portion which can respond to changes in electrical field
What goes down both concentration and chemical gradient?
Na+ ions
What is action potential?
Where the influx of Na+ ions generate action potential upswing
What is resting potential?
Where influx and efflux of charges are balanced
What does the Nernst Equation calculate?
Exact values of the equilibrium potential in Mv
What is the electrical potential?
The work per unit of charge required to move a charge from a reference point to a specified point
What does the electrical potential represent?
Potential in Mv where there is no bet movement of charged molecules in or out of the cell for a given chemical potential
Ek
Normally negative
Ena
Normally positive
What is the equilibrium potential for an ion?
The potential in which no current flows across the membrane
Potential gradient and concentration gradient of the ions cancel out
What is the Nernst Equation?
Ex = RT/ZF x ln ([out]/[in])
What is the reversal potential?
Membrane/Nernst potential of an ion which there is no net flow of a particular ion from one side of the membrane to the other
20 degrees
58.2 log10 [out]/[in]
37 degrees
61.5 log10 [out]/[in]
Define capacitance
How quickly the membrane potential can respond to change in current
Capacitance
How much charge is needed to cross the membrane to give a change in membrane voltage
What happens to current injected into cell?
Most of the current will be used to change the membrane capacitance
Large capacitance
More currents must flow to change the potential across it
Smaller capacitance
Less current must flow to change to potential across it
What is the capacitance taken to be?
1 mF/cm2
Small neurons have a total capacitance of?
25-50 pf
Nodes of Ranvier in large myelinated nerves are around?
1.5 or 2 pF
What is the Goldman-Hodgkin-Katz voltage equation?
Tells you when a membrane is permeable to more than 1 ion simultaneously
What does GHK equation incorporate?
Permeability terms for each of 3 Monovalent ions
What contributes to setting the membrane potential?
Na+
K+
Cl-
What is threshold?
Critical levels to which a membrane potential must be polarised to initiate action potential
What are two types of threshold?
Voltage
Current
What happens in voltage clamp?
The membrane potential is maintained constant or held at a command potential using a negative feedback
What happens in current clamp?
The membrane potential can vary and the current applied is made to follow a command signal
What is the property of cell membrane that holds charge?
Membrane capacity
