L23 - Vesicular Transport Flashcards
What does vesicular transport allow?
Allows movement of molecules between compartments and outside environment
The plasma membrane provides the key barrier to movement of material
What are the two types of vesicular transport?
Endocytosis – allows capture of molecules from outside
Exocytosis – allows secretion of molecules from inside
What is the plasma membrane made of?
Lipids – allow continuity and flexibility of the cell membrane
Protein – traverse the membrane and have transport functions
Carbohydrates – cell protection and tagging (always found on outside)
Cholesterol – helps to seal the plasma membrane preserving internal molecules
Where is cholesterol found in the membrane?
Sits in between two phospholipids
Makes up 17% of the membrane
The lipid bilayer is rich in?
Amphipathic molecules carrying two fatty acids
- Phospholipids
- Sphingomyelin
What are the three types of phospholipids?
Phosphatidyl-ethanolamine
Phosphatidyl-serine – negatively charged
Phosphatidyl-choline
How is membrane flexibility made?
Fully saturated lipids are too rigid
Unsaturated fatty acids provide some disorder and flexibility
- Contain double bonds
Omega 3 structure?
3 double bonds
Produced by sea plants, fish, nuts
Omega 6 structure?
2 double bonds
Produced by land plants and animals
What is the topography of the cell membrane?
Sugars – outside
Negative charge – inside
- Most intracellular molecules and vesicles are negatively charged
- Intrinsically repulsed by each other and plasma membrane
What is phosphatidylserine ?
Key negative charge
The presence of this on the inside of cell membrane is a matter of life or death
How does phosphatidylserine move?
Flips to outer surface only upon apoptosis which takes place during cell death
This flip over can be detected by fluorescent Annexin V test
What two methods do proteins use to interact with the cell membrane?
Transmembrane proteins - Single or multipass - Ion channels Peripheral proteins - Attached to one lipid of the membrane via - Hydrophobic residues - Lipid tail - Other proteins
What is cholesterol transported by?
Low density lipoprotein particles transport cholesterol into cells by receptor mediated endocytosis
Receptor mediated endocytosis method
- Cholesterol molecules derivatised from blood and packed inside LDL molecules
- Protein portion of bilayer recognised by LDL receptors on cell surfaces
- Adapter molecules binds to tail of LDL receptor that protrudes into cytosol
- Adaptin recruits Clathrin to coat membrane
- Membrane invagination and formation of vesicle inside cell - vesicle contains LDL receptors
- Vesicle uncoats and fuses with endosome
- Endosome with acidic pH causes LDL receptors to release cargo
- LDL receptors recycled to plasma membrane and particles dissembled
- Endosomal content delivered to and fuses with lysosome
- Lysosome contains hydrolytic enzymes that digests particle
- Cholesterol released into cytosol - used in synthesis of new membranes
