Vesicular transport Flashcards
required properties of membranes and the roles of omega 3 and 6?
Must be flexible, if they are fully saturated (only single bonds present) they are too rigid.
Omega 3 and 6 are important componants, 6 found in humans. they make the membrane more flexible
Cholesterol - role in the membrane and properties?
Seals the plasma membrane - makes the membrane less rigid. Contains a steroid ring structure. Molecules are polar - they prefer the internal molecules.
TOPOGRAPHY/ARRANGEMENT - of the membrane, how is this established? Phosphatidylserine?
Sugars are on the outside of the the membrane, and -vely charged elements on the inside. These intrinsically repulse each other.
PHOSPHATIDYLSERINE is found on the inner surface (-ve) and flips to the outside during APOPTOSIS. The presence of it dictates life or death.
Endocytosis and nutrient uptake - how does this happen? LDL and cholesterol
LDL is transported by cholesterol in the blood. When LDLs bind to the cell membrane, the membrane invaginates and a coated vesicle forms.
Receptor mediated endocytosis - process and role of adaptors and clathrin?
LDL binds LDL receptors on the cell membrane. Adaptors bind to the receptor intracellularly. The adaptors are bound to clathrin which is needed to form coated vesicles. The vesicle fuses with lysosomes, which causes LDLs to break down and cholesterol to be freed.
PIP2 - role and where is it found?
Found on the inner leaflet of cell membrane, it is a signalling lipid. Activated by PI kinase adding a sugar to it. (this occurs when PI kinase is activated at the membrane by a ligand binding to the PI receptor.)
DEFECTIVE ENDOCYTOSIS - example = cholesterol. Familial atherosclerosis.
Mutations in the LDL receptor - the receptor cannot interact with the adaptor (which recruits clathrin to form coated vesicles).
This causes lipoproteins to accumulate in the blood and plaques to form which block arteries
CLATHRIN - role? how it is linked to functioning of dynamin?
forces invagination of the cell membrane, and helps vesicles to form. Causes membrane to pinch off, under influence of DYNAMIN. When dynamin GTP->GDP, membrane is pinched off. Mutations in dynamin protein - vesicles cannot pinch off
PHAGOCYTOSIS - relation to vesicle formation?
in phagocytosis vesicles form WITHOUT CLATHRIN - so that phagosomes can engulf the bacteria and fuse with lysosomes and hydrolytic enzymes break down the bacteria.
AUTOPHAGY - what does it do? SNARES!
elimination of malfunctioning cell elements (vesicles fuse and engulf organelles).
Involves fusion of internal membrane compartments - done by SNARES!!!!
EXOCYTOSIS - where is it used? how is it regulated? Insulin as an example
Neuronal communication, hormone secretion and secretion of digestive enzymes.
Regulated - highly concentrated insulin is released in vesicles in response to high glucose. Insulin is produced in pancreatic B-cells, at the islets of langerhans in the liver.
-VE INTERNAL REPULSIVE FORCES - SNARES! how do they overcome this?
SNARES are proteins which aid in fusion of vesicles. The SNARES wrap around each other and force membranes together.
SNARES - types?
T snares - syntaxin and SNAP 25. These are found on the plasma membrane.
v snares - synaptobrevin and VAMP. These are found on the surface of vesicles.
SNARES - structure? What structure do they form upon contact? NSF enzyme?
SNARES are long chain amino acid structures which form 4 coiled-coil helix upon contact.
In the helices, 1 synataxin is found, 2 SNAP25s and 1 VAMP.
The NSF enzyme catalyses dissociation of SNARE coils (by ATP hydrolysis).
BOTULINUM - what does it do? How does it cause paralysis?
BOTULINUM is a neurotoxin which is found in contaminated food and cleaves t SNARE SNAP25, so vesicles containing NT cannot fuse with the post synaptic membrane and muscle paralysis is caused.
