What is the Golgi job?

Answer 1

The Golgi apparatus, transports and organizes proteins.

The Golgi traffics proteins made in the ER to the Golgi which then modifies them and sends them out to the cell wall. This is called the secretory pathway.

The secretory pathway was mostly discovered by a man names Palade, he confirmed th existence of ribosomes. He used radioactive lysine which is called a pulse-chase experiment: Autoradiolgraphy provided evidence that proteins must go through the Golgi and that the mitochondria produced its own proteins. Once you radiolable the amino acid you can see where it goes through microscopy and you can also detect different modifications it goes through via an SDS page and a immunoprecipitate and another important technique is called the density gradient centrifuging. This type of differentiation though can only get the Golgi or microsomes (er).

Lets talk about how the actual process occurs. N-linked glycosylation happens in the ER and is then tagged for transport to the Golgi apperatus. Firstly proteins cannot escape the secretory pathway then can go outside in the cytoplam. What is in the Golgi stays in the Golgi. So SAR 1 gets GTD to GDP from a transmembrane domain called SEC 12 then once it has GTP it can bind into the membrane and bind to SEC 23/24 which is involved in getting the actual cargo. Cargo binds to this SEC 23/24 and then binds SEC 13/31 which then pinches off the membrane. Once Sar 1 gets GTP to GDP the COPII coat dissociates to that all the little vesicals can form a VTC which is a pre-Golgi intermediate vessicle. So ER proteins lacking transmembranes domaisn connect interact directly with COPII SEC 23/24/ They must interact with ERGIC53 which is a corgo receptor that binds the N-linked oligosaccharides. Very few ER proteins are glysosylated. They return to the ER by retrograde because the cargo receptors can interact with CAP1. Basically COPI just recylces proteins to the ER.

The vesicles move via moterproteisn like Dynesin to the Golgi from the ER.

Nlinked oligosaccharides are needed to leave the VTC. VTC is almost a minature Golgi apperatus, the VTC is the pre-Golgi versicle.

Once they arrive at the CIS-Golgi. The Golgi has 2 sections CIS and TRANS.

They arrive in CIS and then travel to TRANS. Which there is contraversy about.

The three main ideas are that of Intra Golgi trafficing are as follows.

Simple Diffusion through the Cysternae of the Golgi. The cis cisternae could gradually mature to become the trans cisternae. (this was once a plausible because they saw the trans Golgi peeling off but now is unliked because they don't know how the enzymes stay in there approptiate cysternea)

Then Rothman had dicovered the COP1 he proprosesed that the cargo just gets moved from one cysternae to another cia COP1 protein coat.

Another experiement was done with stomatis virus G protein that linked the idea of maturation because all the contents stayed together. Either 2 ways are not looked at

1 Cop1 moves the enzymes back

2 The cysterane are linked together and they diffuse. Through either staying where they are needed or by the cholesterol pH gradient. pH is higher in the Trans.

So once they are inside the Golgi cargo is processed. Sequential modification of the N-linked gylcosylation, the addition of an O-linked and and proteoglycan.

So the N-acetylglucosamine GlcNac is the O-linked glycosilation that is added to the -OH on the serine. - happens in the middle.

The removable mannose happens in CIS. along with sorting and phosphorlation

The Galactose and the N-acetylneuraminic acid. - happen in the trans cisterna

A good test to see if a cargo went through the Golgi is to use Endo-H. BEcause of the Nlink it will be resistance because of modification.

All the proteolytic modifications required an acidic pH

and remains acidic because of ATPase, raflomicin blacks this activity.

Sorting.

They are organized by kinasan molecules and are secreted to the baso or apical by membrane protein in the Trans Golgi.

Budding from the Trans Golgi

Cathrin is an important protein for the budding. Lipid rafts often found in the Trans Golgi that have proteins for export. Catherins are baskets used for endosomes and budding of the Golgi they are recruited by adapter proteins called AP1-3-4 and GGA.

GGP soluble proteins AP3 proteins to the endosomes lysosomes, they help with the sorting as well as get clathrins.

Once the catherins pinch of from the Golgi they Arf1 goes to GTP and de-coats and you get fusion of the wall and protein expulsion.