Membrane trafficking Flashcards
Concepts; Exocytosis; Endocytosis; Molecular mechanisms
Define exocytosis
Export of molecules contained in vesicles to outside of cells
Constituative or regulated
Define endocytosis
Import of molecules from outside of cell into vesicles
early endosome→late endosome→lysosome
Receptor mediated or pinocytosis or phagocytosis
What is constituative secretion?
All cells
Steady vesicle stream from Golgi
Fusing with plasma membrane
What is regulated secretion?
Excitable cells
Products concentrated and stored in secretory vesicles until signal stimulates secretion
What are the purposes of the two locations of ribosomes in a cell?
Free ribosomes - make proteins for internal cell use
ER bound ribosomes - make proteins for secretion/use within plasma/lysosome
What is the process of receptor mediated endocytosis in the case of cholesterol from LDLs?
1) LDL receptors on membrane bind to LDL
2) LDL swallowed into clarithrin coated pit to form vesicle
3) Dynamin helps vesicle pinch off membrane
4) Vesicle is uncoated and fuses with endosome
5) LDL particles delivered to lysosomes for degredation
6) Receptors bud off and return to the membrane
How is a protein mid translation directed to the correct area in the cell?
Protein being made has a signal peptide/signal sequence/localisation signal to direct it to correct cell compartment
Where are proteins modified and how?
ER Folding Disuphide bond formation Initial glycosylation Specific proteolytic cleavages Assembly of multimeric proteins Incorrectly folded are blocked from exit
What is the process of exocytosis?
secretory protein→ER→vesicle→golgi→Trans golgi network→vesicle→out of cell
What happens in the golgi apparatus?
Further protein modification, particularly to sugar molecules added in rER
What is gated transport?
Proteins and other substances move in and out of the nucleus via nuclear pores, which act as gates with mesh like structures
How are vesicles transported?
Carried on microtubules to other organelles
Vesicle tethering/docking proteins bring vesicle and target membrane close together
How close do membranes need to be to fuse?
1.5nm apart
What diseases can be involved in membrane transport?
Familial hypercholestrolaemia - endocytosis
Cystic fibrosis - exocytosis
How does familial hypercholesterolaemia affect endocytosis?
LDL receptor not produced/not functional
Cannot remove LDL from blood
