Lecture 1 - Membrane Bilayer Structure Flashcards
What are the major functions of biological membranes?
Highly selective permeable barrier
Controls enclosed electrochemical environment
COMMUNICATION
Generating signals in response to stimuli
How are membranes involved in communication?
Recognition
Signalling
Adhesion proteins
Immune surveillance
How would you describe the structure of a cell membrane generally?
A dynamic fluid phospholipid bilayer with proteins and additional structures
What is meant by membranes being heterogenous within and between cells?
The structure and therefore undying function of membranes are different based on the cells/organelles function
What types of molecules are cell membranes made up of?
Lipids
Proteins
Carbohydrates
What is a major component of the cell membrane?
Water
Membranes are hydrated structures
What is the role of water in hydrating membranes?
It interacts with the charged/polar regions
This stabilises the lipid head regions of the bilayer
What are the 3 types of lipids that can compromise cell membranes?
Phospholipids
Glycolipids
Cholesterol
What is the difference between saturated and unsaturated phospholipids making up the cell membrane?
Saturated have single C-C bonds in the fatty acid chains
Unsaturated have some C=C bonds in the fatty acid chains
What are the 2 structural forms of unsaturated phospholipids?
Cis
Trans
What is the structure of a Cis phospholipid?
One of the fatty acid chains is kinked at the point of the double bond
Which is the structure of a trans phospholipid?
Double C=C bond where the fatty acid chains are straight
What is the name of a type of glycolipid?
Ganglioside
What does Amphipathic mean?
One part of the molecule is hydrophilic
One part of the molecule is hydrophobic
What is amphipathic about the cell membrane?
The polar (hydrophilic) heads
The non polar (hydrophobic) fatty acid chains of the bilayer
What is a Micelle?
3D sphere of phospholipids
What is the main type of phospholipid that makes up the cell membrane?
Glycerophospholipids
What is the structure of a Glycerophospholipid?
Polar phosphate group = hydrophilic head
Glycerol backbone
Fatty acid chains (hydrophobic tail)
What property of glycerol in a phospholipid allows the polar phosphate head and hydrophobic fatty acid tails to swivel?
The single bonds in glycerol
What is esterification?
An acid group being added to an alcohol group
Which group of fatty acid chains can interact with water?
-C=O (acyl group)
What are 2 common polar head groups that can be found attached to the phosphate group?
Choline
Inositol
What type of molecule is sphingomyelin?
Phospholipid
What is different between a sphingomyelin molecule and a glycerophospholipid?
Sphingomyelin does not have a glycerol backbone, it has a Sphingosine molecule instead
What process does sphingomyelin have a key role in?
Lipid raft formation
What are the 2 types of glycolipids?
Cerebrosides
Gangliosides
What is special about glycolipids structurally?
No glycerol backbone (sphingosine)
No phosphate group
Where are cerebrosides and gangliosides mainly found?
CNS/PNS
On the membrane, where are sphingomyelin and glycolipids found?
On the outer face of the membrane
What is the structure/properties of cholesterol?
Amphipathic
Hydrophilic -OH head
Hydrophobic 4 planar carbon rings and short fatty acid tail
What is the key membrane function of cholesterol?
Regulates membrane fluidity and stability by enhancing/extending temerature range that the membrane is thermodynamically stable
Lipid raft formation
What is the key membrane function of cholesterol?
Regulates membrane fluidity and stability by enhancing/extending temerature range that the membrane is thermodynamically stable
Lipid raft formation
What is membrane fluidity?
The property of the cell membrane that allows it to adapt its shape and movement to different conditions
What happens when the cell membrane is too fluid?
There is a loss of molecular organisation needed for membrane/protein function
What happens when the membrane is not fluid enough and is gel like?
It restricts and constrains the mobility of proteins and restricts the ability for diffusion to take place
What is the main Physical factor affecting membrane fluidity, name another factor?
Temperature
Molecular mass of phospholipid
What are the ways that individual phospholipid molecules move?
Individual chain bond Flexion/vibration (wobbly bob)
Fast axial rotation (whole lipid spins on head)
Fast lateral diffusion (lipid moves randomly through bilayer
Protrusion (Bobbing up and down)
Flip-flop
How is vibration/movement of phospholipid molecules affected by temperature and molecular mass?
Higher temp = higher vibration
Higher molecular mass = less vibration
How do cell membrane bilayers behave that have saturated phospholipids at 37ºC?
Fluid behaviour
How does adding unsaturated phospholipid to a membrane bilayer affect its fluidity?
Decreases the temperature by which the membrane changes form a gel to fluid state
INCREASES FLUIDITY
How does adding unsaturated phospholipids to cell membrane increase its fluidity?
Due to the cis C=C bond with kink
Less dense packing of fatty acid tails
At high temperatures, what type of movement of phospholipids happens too much causing the structural integrity of the membrane to become too disordered?
Increased bond chain Flexion/vibration
What does cholesterol due to the range of fluidity?
Increases range by making membrane fluid at lower temperatures
How does cholesterol stabilise the membrane at higher temperatures?
-OH polar group of cholesterol binds to acyl group of phospholipid head
Rigid carbon rings limits movement of fatty acid tails
How does cholesterol increase the fluidity of the membrane at low temperatures?
Interferes with crystalline packing of the fatty acid chainns
How is water important in the structure of the membrane?
It dynamically interacts with the membrane
What is a lipid raft?
Areas of organised/specialised distribution of lipids in cell membranes
What molecules are increased in numbers in lipid rafts?
Cholesterol
Sphingomyelin
Glycolipids
What is the role of lipid rafts?
Role in stabilising and organising proteins
Domains for receptors and signalling molecules
What is the importance of the membrane fluid and flexible?
Protein function
Able to transmit force throughout cell structures
Why is it important for forces to be distribute throughout the whole body?
Excessive force that is localised can cause damage
