golgi apparatus

Question 1

what is the golgi

Answer 1

A basket or ribbon-like organelle located at the perinuclear region.

Organized around the centrosome/Microtubule Organizing Centre (MTOC)

Golgi receives newly synthesized and correctly assembled secretory cargo proteins from the ER.
* Proteins are further modified and sorted for transport to various cellular compartments including plasma membrane

Question 2

modular compartments

Answer 2

cis - medial - trans

the cis-golgi network (CGN) and trans-golgi network (TGN). Thus, golgi is a
polarized organelle.

cis receives vesicles from ER
processed/modified/tagged as they move through stack
cargo packaged and leaves golgi from trans face

Question 3

Golgins

Answer 3

coiled coil protein with extended rod-like conformation (tethering).

Question 4

GRASPS

Answer 4

Golgi Reassembly and Stacking Proteins.
Membrane associated proteins that dimerize/oligomerize. (stacking protein to hold parallel cisternae together)

Question 5

Requirement for microtubules

Answer 5

Intact microtubule network is required
to maintain:
1) ribbon structure
2) perinuclear localization

Question 6

Formation of the golgi ribbon

Answer 6

Microtubule network and microtubule
dependent transport clusters golgi ministacks at the perinuclear region.

Tethering protein (golgins) then draw
mini-stacks into close proximity to allow
membrane fusion.

Golgi membrane fusion likely by SNARE
mediated docking mechanism as with
vesicle membrane fusion (Module 4)

Question 7

Golgi Transport: ER to the golgi

Answer 7

A protein ‘coat’ drives budding of
ER membrane to form the
vesicle.

Coat needs to disassemble prior
to membrane fusion at target
organelle.

COPII coated vesicles move
from ER to golgi (anterograde
transport)

COPI vesicles move in reverse
direction (retrograde transport).

Coat proteins also sort specific cargo for transport

Question 8

Sorting cargo for transport.

Answer 8

sorting signal on cytoplasmic domain of membrane cargo proteins

Soluble cargo proteins with luminal sorting signals require recognition by membrane cargo receptors for transport selection

Question 9

Retrograde retrieval

Answer 9

this needs to happen in case ER only proteins accidentally end up in golgi

they have a sorting signal – KDEL sequence
this binds well in golgi because of low pH, but when it arrives back in ER it detaches because of high pH

Question 10

Glycosylation in Golgi

Answer 10

Glycosidases remove and
glycosyltransferases add individual
sugars to the chain.

cis-Golgi glycans become
substrates for medial golgi
enzymes - medial becomes substrates for trans etc.

Question 11

Cisternal maturation

Answer 11

the sugars dont actually move, the compartments move around them and the operators in the machine line (e.g. ) also move.

cis-golgi enzymes retrieved from medial
compartment by COPI vesicles moving in retrograde fashion.
- Medial-golgi enzymes retrieved from transcompartment in same way.