L3 - Through and out the golgi

Question 1

what are the 2 mnodels of movement through the golgi

Answer 1

Cisternal maturation:
cargo moves WITH maturing cisternae through stack –> sorted and bud off at TGN + golgi enzymes transported back

Vesicle transport:
golgi cisternae are static compartments –> cargo move forward in vesicles

Question 2

describe the cisternal maturation model

Answer 2

acts like conveyor belt

= cisternae mature and move though golgi PULLING cargo with it

Question 3

describe the comnpartments of golgi in cisternal maturation model

Answer 3

each comopartment has its own function

–> means that as cisternae move through ‘conveyer belt’ and mature

= to be able to do the modifications proposed in each stage
= COP1 moves the needed enyzmes between cisternae compartments as needed

Question 4

describe the vesicle transport model for movement within golgi

Answer 4

Cisternae compartments are NOT dynamic - do not mature

= maintain same resident enzymes for modelling at all times

Cargo is moved via vesicular transport - COP1

Question 5

what is the TGN

Answer 5

Trans-Golgi Network

= cargo sorting centre at the end of golgi

Question 6

what pathway would proteins modified with mannose-6-phosohate be directed to by TGN

Answer 6

lysosomal protein degredation

1. proteins with M6P collected in clathrin coated vesicles

= diverted via endosomes to lysosomes –> cargo includes acid-hydrolyases for lysosomal protein degrefation

Question 7

describe the default/constituitive pathway from TGN

Answer 7

material transported to membrane in non-specialised manner

1. accumation of cargo at specifc sites of TGN

= UNREGULATED secretion to membrane

Question 8

describe the specialised secretory signal pathway at TGN

Answer 8

proteins with special secretory signals packaged into vesiucles for REGULATED secretion

= neurotransmitters or signal molecules (insulin)

Question 9

what tag is added post-translationally as a tag for enzymes/proteins put into lysosomal degredative pathway from TGN

Answer 9

Mannose-6-phosphate

= cargo is mainly acid-hydrolases

Question 10

describe the lysosomal pathway from TGN

Answer 10

1. M6P recognised by receptors and bind
2. clathrin coat binds to receptor:M6P

= packaged into vesicles

3. trafficked to ealy endosomal system
4. As early endosomes mature pH drops –> M6P disosociates from receptor + drops coat

= coat and receptor tarfficked BACK to TGN

Question 11

what are the 4 main stages in clathrin coat assembly/disassembly

Answer 11

1. Coat assembly + Cargo selection
2. Bud formation
3. Vesicle formation
4. Uncoating

Question 12

describe tghe assembly and disaambly of the clathrin coat

Answer 12

1. Cargo receptor bound to desired cargo on membrane of golgi
2. Clathrin adaptor complexes bind

= selevtive recognition of cargo receptor AND lipid component of membrane

3. cargo receptors collectyed and calthrin binds to the adaptors –> triskelion
4. pinching off by membrane bending and fission proteins

= vesicle formed

Question 13

what are clathrin adaptor complexes

Answer 13

multi-subunit complexes

Different adaptors to different compartments

= same function as Sec23/24 heterodimer in COP2 –> bind to cargo receptor AND then Coat protein (clathrin or COP2) binds

= AP-2 adaptor for trafficking to plasmam membrane

Question 14

what enables Clathrin to bind to a wide range of Clathrin-adaptor proteins

Answer 14

globular domain of clathrin heavy chain is a binding site for MULTIPLE adaptors

Question 15

explain Co-incidience and how it plays a role in specificity for clathrin recruitment

Answer 15

Adaptor proteins interact with PHOSPHOLIPIDS + proteins with SPECIFIC SORTING MOTIF

1. Ap2 adaptor binds to PIP2 phospholipid
2. Ap2 is activated

= comformational change revealing binding motifs

3. binding motifs bind to sorting motif –> initiate coat formation

Question 16

what is dynamin

Answer 16

GTPase used to cut/pinch off vesicle

= self asseembles into tubular polymers
= comformational chnage –> scission