3.5 - Protein Trafficking from Golgi

Question 1

types of secretion from golgi (2)

Answer 1

1. constitutive
2. regulated

Question 2

constitutive secretion

Answer 2

vesicles move directly from golgi to plasma membrane

Question 3

regulated secretion

Answer 3

fusion of vesicles with plasma membrane depends on signal

Question 4

regulated secretion example

Answer 4

insulin secretion in beta cells of pancreas

Question 5

how is insulin secretion in beta cells of pancreas triggered by rise in blood glucose? (4)

Answer 5

1. uptake of glucose by GLUT2 transporter
2. glycolysis leads to rise in ATP:ADP ratio
3. inactivates K+ channel, depolarising membrane causing Ca2+ channels to open
4. rise in Ca2+ causes insulin release from vesicles (SNAREs activated by Ca2+)

Question 6

lysosome

Answer 6

membrane-bound sacs of hydrolytic enzymes

Question 7

examples of lysosomes digesting extracellular material and worn out cellular organelles (3)

Answer 7

1. endocytosis
2. phagocytosis
3. autophagy

Question 8

how do lysosomes maintain a low pH?

Answer 8

ATP-driven pump of H+ into lumen

Question 9

why does the lysosome lumen have a low pH?

Answer 9

collection of hydrolytic enzymes active in acidic conditions

Question 10

purpose of transporters in lysosome membrane

Answer 10

transfer sugars, amino acids, nucleotides to cytoplasm

Question 11

why are lysosomes made as inactive precursors with an extra peptide

Answer 11

because theyre dangerous?

Question 12

lysosome activation

Answer 12

extra peptide cleaved off

Question 13

what recognise lysosomal proteins in cis-golgi?

Answer 13

sorting patch

Question 14

how does sorting patch recognise recognise lysosomal proteins in cis-golgi? (2)

Answer 14

1. add P-GIcNAc to mannose on N-linked sugar
2. then remove GIcNAc - mannose-6-phosphate

Question 15

role of dynamin in vesicle formation (pinching off)

Answer 15

dynamin polymerises around neck (vesicle separates from membrane)

Question 16

what drives conformational change in dynamin (pinching off)

Answer 16

GTP hydrolysis

Question 17

examples of cell surface to lysosome endocytosis (2)

Answer 17

1. phagocytosis
2. receptor-mediated endocytosis

Question 18

endosome

Answer 18

first destination for endocytic vesicles

Question 19

role of endosome

Answer 19

sorting station for endocytic pathway (some molecules sent to lysosome some recycled)

Question 20

how does endosome determine where vesicles are next transported?

Answer 20

depends whether ligand and receptor within vesicle membrane endocytosed stay associated

Question 21

endosome transport if receptor bound for recycling?

Answer 21

vesicle will go there

Question 22

endosome transport if receptor bound for transfer to other side of cell

Answer 22

they will transcytose

Question 23

endosome transport if receptor and ligand do not remain bound due to acidic nature of endosome

Answer 23

will go to lysosome for degradation

Question 24

lipoprotein particle

Answer 24

‘packages’ of lipids and cholesterol bound by apoprotein B-100

Question 25

low density lipoprotein (LDL)

Answer 25

'bad cholesterol'

Question 26

LDL receptor

Answer 26

transmembrane protein

Question 27

LDL receptor role (4)

Answer 27

1. binds to LDL outside cell and adaptins inside cell 2. adaptins bind clathrin 3. LDL internalised in coated vesicles 4. delivered to lysosomes

Question 28

what can a mutation in the LDL receptor cause?

Answer 28

no binding to adaptin

Question 29

aim of transferrin receptor

Answer 29

get iron into cell

Question 30

components of transferrin receptor (3)

Answer 30

1. Fe3+ ions 2. transferrin 3. transferrin receptor

Question 31

iron-dependant binding in transferrin receptor

Answer 31

transferrin to receptor

Question 32

pH-dependant binding in transferrin receptor

Answer 32

Fe3+ to transferrin, transferrin to receptor

Question 33

pH of endosomes

Answer 33

acidic

Question 34

EGF receptor

Answer 34

'epidermal' growth factor receptor

Question 35

EGF receptor role (4)

Answer 35

1. EGF binds 2. receptor becomes dimer 3. tyrosine kinase phosphorylates itself 4. cells proliferate

Question 36

epidermal growth factor

Answer 36

'on' switch for cell proliferation

Question 37

'off' switch for cell proliferation

Answer 37

endocytosis of EGF and receptor to lysosome

Question 38

familial hypercholesterolaemia (3)

Answer 38

1. lots of LDL and receptor 2. receptor spread all over cell surface, not in clathrin coated pits 3. mutation Y in cytoplasmic region impacting adaptin binding signal

Question 39

mannose-6-phosphate disease example

Answer 39

mucolipidosis II

Question 40

LDL receptor disease example

Answer 40

familial hypercholesterolaemia

Question 41

mucolipidosis II (2)

Answer 41

1. lysosomal enzymes secreted into bloodstream 2. defect in GIcNAc phosphotransferase

Question 42

protein involved in cystic fibrosis

Answer 42

ATP-dependant chloride channel

Question 43

most common mutation causing cystic fibrosis

Answer 43

∆F508

Question 44

result of mutation causing cystic fibrosis

Answer 44

ATP-dependant chloride channel protein unable to stay in first place

Question 45

problem with protein folding involved in cystic fibrosis

Answer 45

cytoplasmic chaperones stuck on and cant enter COPII vesicles (most of protein on cytoplasmic side)