Receptors and Endocytosis Flashcards
Define endocytosis
Transport of molecule into cell by membrane invagination
What does phagocytosis need?
Specialised cells (specific)
What is receptor-mediated endocytosis?
Any specific cell
What is pinocytosis?
Any non-specific cell
What are the steps of phagocytosis?
Recognition/Adherence/Engulfment/Digestion
Name some specialised cells linked to phagocytosis
Macrophages, Neutrophils
Describe the process of phagocytosis
Only by specialised cells
Pathogen associated molecular pattern (PAM’s) binds with a Toll-like receptor
Describe the structure of clathrin molecules
Macromolecular cages
Composed of three-legged units (triskelions)
Lattice of hexagons/pentagons (soccer ball)
What do clathrin-coated vesicles transport?
selected integral membrane proteins from cell surface and trans-Golgi network to endosomal system
In terms of scission, What is dynamin?
Large GTPase involved in budding, scission nascent vesicles from parent membranes
What is bin-amphiphysin-rvs (BAR)?
Proteins bind to membrane, sculpt the curvature
Describe BAR
Domain is one of the main links btw membranes/actin cytoskeleton
BAR proteins sense membrane curvature, recruit actin to membranes, interact with GTPase dynamin which mediates vesicle fission
Describe the energy dependent step (uncoating)
Auxilin binds with high affinity to assembled clathrin lattices with ATP
Together they distrupt protein-protein interactions in clathrin lattice
What are SNARE proteins?
Soluble protein receptors
Describe the function of SNARE proteins
Mediate fusion of vesicles structures
Vesicle deliver cargo to target membrane bound structures
What do SNARE proteins tether?
Target membrane and vesicle, support fusion
What can be formed from SNARE proteins?
Vesicle and target SNARE proteins form tight a-helical bundle - SNARE complex disassembled and recycled
In terms of SNARE disassembly, what is cytoplamic?
NSF is thought to disassemble the SNARE complex using ATP as an energy source
Describe the clathrin-independent process and what it contributes to
Major contributor to fluid uptake in cells/membrane repair
Contributes to cellular polarisation, motility, regulation of signalling, normal cell growth
What are the mechanisms involved with clathrin-independent processes?
Caveolae - Involves caveolin/lipid rafts
Macropinocytosis - Large vesicles
Describe what happens after internalisation
Fusion with early endosomes, Importance of pH
Different processing pathways - Recycling to plasma membrane, Degradation by lysosomal enzymes, Transcytosis
Name some examples of delivery of cholesterol and iron to tissues
Low density lipoprotein (LDL)
Transcytosis of antibodies
Familial hypercholesterolaemia - Autosomal dominant genetic disorder by chr19 mutation = Defect in LDL receptor, causes high level of LDL in blood
Describe transferrin
Carries iron in blood, lower pH in endosome causes trans to release its iron, receptor recycled into plasma membrane, dissociates from receptor when in pH7 outside cell
Describe transcytosis
Movement of macromolecules btw cells (across endo of blood vessels)
For caveolae/clathrin-mediated processes, Regulates SNARE proteins, cytoskeleton, lipids
