Fluid Mosaic Model, Membrane Dynamics (Lecture 15) Flashcards
What are the two basic cell types?
In what way do the cells for together?
Cell components are ___________ across species
What are viruses?
What do viruses help us understand?
- 2 basics cell types: Prokaryotic and Eukaryotic
- Cells parts work together in a precise way
- Cell components are conserved across species
- Viruses are macromolecular packages that contain enough information to hijack the cellular machinery
- Viruses help us understand complex cell processes
What is the structure of the Fluid Mosaic Model?
What is the lipid bilayer made up of?
What is embedded in the phospholipid bilayer?
- The trilaminar structure is a lipid bilayer
- The lipid bilayer is made up of phospholipids
- Proteins are embedded in the phospholipid bilayer
The fluid mosaic model of biological membranes
What does “fluid” mean?
What does “mosaic” mean?
Fluid - individual lipid molecules move
Mosaic - diverse ‘particles’ penetrate the lipid layer
The Fluid-Mosaic Model of biological membranes
What are the main parts of the fluid mosaic model?
Structure of Biological Membranes
The fluid mosaic model, who discovered it, and in what year?
What kind of lipid make up the fluid mosaic model? Proteins?
- Fluid-Mosaic Model (Singer/Nicolson, 1972)
- Bilayer of amphipathic lipids
- Proteins
- Integral (Transmembrane)
- Peripheral
- Lipid-anchored
What does amphipathic mean?
amphipathic - having both hydrophobic (non-polar) & hydrophilic (polar) regions
Biological Membranes are Dynamic
How do lipids move?
What happens with membrane proteins within the bilayer?
- lipids move easily, laterally, within the leaflet
- lipid movement to other leaflet is slow
- membrane proteins diffuse within the bilayer
- movement of proteins is restricted spatially
- long-range diffusion is slow
- biochemical modification can alter protein mobility in the membrane (important for signal transduction)
Biological Membranes are Dynamic
What do biological membranes contain?
Biological membranes contain a hydrated lipid bilayer
Where is the water in a soap bubble and a lipid vesicle?
Where does the tail point in a soap bubble and lipid vesicles?
Soap bubble - Water inside, tail pointing out
Lipid vesicle - Water outside, tail pointing in
Phospholipids have hydrophilic and hydrophobic components
How can phospholipids be represented?
What consists of the Polar head group?
What consists of the Nonpolar tail?
- Phospholipids can be represented in a variety of ways to emphasize overall structure, different domains, and 3D shape
- Polar head group
- Hydrophilic
- Choline
- Phosphate
- Glycerol backbone
- Nonpolar tail
- Hydrophobic
- Fatty acid chains
Structure of Biological Membranes
An example of differential membrane structure:
What does the inner membrane of mitochondria contain?
What does the Myelin sheath contain?
- The inner membrane of mitochondria contains a very high concentration of protein
- The myelin sheath of a neuron contains very low amounts of protein.
- Myelin sheath consists of layers of plasma membrane, forming insulation around the nerve axon.
What does this micrograph show?
Below: Electron micrograph of a nerve cell axon (cross-section) showing myelin sheath, a modified plasma membrane structure.
Top blank: Axon
Left blank: Myelin
Right blank: Oligodendrocyte
What are the 3 Classes of Membrane Proteins and their locations?
- Integral
- membrane proteins span the lipid bilayer
- Peripheral
- membrane proteins associate with the surfaces of the lipid bilayer
- Lipid-Anchored
- proteins attach to a lipid in the bilayer
Different integral (transmembrane) proteins have different functions; e.g?
- Transport
- Cell-cell communication
- Attachment
Biological Membranes are Asymmetrical what does this mean?
Biological Membranes are Asymmetrical
- Two leaflets have distinct lipid composition
- In many plasma membranes, the outer leaflet contains glycolipids and glycoproteins
(lipids and proteins with carbohydrate attached)
Label the diagram
Fluidity: an Important Feature of Biological Membranes
How does temperature affect fluidity?
What is membrane fluidity determined by?
- Temperature
- Warming increases fluidity
- = liquid crystal
- Cooling decreases fluidity
- = crystalline gel
- Warming increases fluidity
- Membrane fluidity is determined by:
- Nature of lipids in a membrane
- unsaturated lipids increase fluidity
- saturated lipids reduce fluidity
- Nature of lipids in a membrane
How does transition temperature affect fluidity?
Which state are these phospholipids in?
- Cool
- Gel-like consistency
- Crystalline gel state
- Warm
- Fluidlike consistency
- Liquid crystal state
Why is membrane fluidity crucial to cell function?
- membrane fluidity must be maintained
- in response to changes in temperature, lipid composition of membranes can be changed by:
- 1) desaturation of lipids
- 2) exchange of lipid chains
What is the difference between saturated and unsaturated fatty acids?
Saturated fatty acids chains lack double bonds, resulting in phospholipids with a straight structure that favors tight packing
Unsaturated fatty acids have one or more double bonds that introduce kinks in the phospholipids, reducing the tightness of packing
What are the dynamic properties of the plasma membrane?
- A leukocyte ingesting a yeast cell
- White Blood Cell (Neutrophil) “chasing” bacteria
How does cholesterol modulate membrane fluidity?
What does the amphipathic structure of cholesterol allow?
Cholesterol modulates membrane fluidity
- alters packing and flexibility of lipids
- if added to a liquid crystal membrane, the fluidity will decrease
- if added to a crystalline gel membrane, the fluidity will increase
The amphipathic structure of cholesterol allows it to pack tightly with phospholipids
