membrane trafficking

Question 1

define exocytosis

Answer 1

removal of substances from cells in vesicles which fuse to the plasma membrane

Question 2

define endocytosis

Answer 2

movement of materials into the cell that were captured in the external medium

Question 3

define constitutive excretion

Answer 3

all cells
constant
steady stream from Golgi

Question 4

define regulated secretion

Answer 4

excited cells (neurons/mast cells) - stimulus
hormones and chemical signals
product stored in secretory vesicles until extracellular signal

Question 5

summarise the pathway and cellular locations for synthesis, post-translational modification and exocytosis of a secreted protein

Answer 5

signal sequence that directs mRNA to RER
signal recognition particle
cleaved in ER
ER - post-translational modification
move to cis face of Golgi - packaged into secretory vesicles
motor proteins move vesicles along membrane until tether to correct acceptor compartment
exit trans face of Golgi - bind to plasma membrane
bud from membranes have distinctive protein coat [coated vesicles]
after budding coat is shed - clathrin coated

Question 6

formation of clathrin-coated vesicles

Answer 6

invagination

dymanin - ring - causes ring to constrict - pinch off vesicle

Question 7

what happens in the ER

Answer 7

unassembled/misfolded proteins retained and exported to cytosol where degraded
modifications: folding, formation of disulphide bond, glycosylation, proteolytic cleavages, assembly of multimeric proteins

Question 8

what happens in the Golgi

Answer 8

sugar chains need to go under further modifications

Question 9

summarise the process of receptor-mediated endocytosis and the roles played by endocytic vesicles, early endosomes, late endosomes and lysosomes

Answer 9

vesicle bind to receptor
enters cell
enter endosome - pH 5 cause receptor and vesicle to dissociate
receptor goes into a transport vesicle and is recycled on the plasma membrane
material is ready for function
uncoating of clathrin
early endosomes fuse with late endosomes nearer the nucleus
pH maintained by ATP driven proton pump

Question 10

mechanisms of vesicular transport in cells

Answer 10

actin filaments - cytoskeleton motor proteins
gated transport: nuclear pore, local nuclear signal, import receptor and go through pore, filamentous protein into cytosol, mesh like structure
vesicular transport: organised budding and fusion, tether/dock on acceptor compartment membrane - 1.5mm away

Question 11

familial hypercholesterolaemia

Answer 11

receptor mediated endocytosis
receptor not present/not functional
can’t take up LDL
atherosclerosis

Question 12

cystic fibrosis

Answer 12

receptor not present
ABC transporter class protein channel mutation affect functioning of chloride channel
CFTR degraded

Question 13

SMED-SL

Answer 13

DDR2 - kinase receptor for collagen, degraded
mutations have similar localisation
dwarfism