Lecture 17 Part 2 - Golgi Apparatus And Vescicular Transport Flashcards
State the characteristics of Golgi complex
1- stack of flattened sacs (cisternae) similar in RER
2- located between the endoplasmic reticulum and the cell surface
3- divided into several compartments
4 - called the sorting post
Polarity of golgi complex
Cis face of the golgi faces the ER - receiving end of golgi
The trans face is on the opposite side of the stack- exiting side of golgi
Functions of golgi
- sorts proteins for export to other secretory pathway organelles or outside of the cell
- to Make Glycoproteins- add sugar to proteins
- make complex carbohydrates to be exported from the cell ( especially in plants )
- modifications
Golgi is named after
Camillo golgi
Which cell doesn’t have Golgi
RBC
Function of receiving end of golgi ( CGN )
Sorts proteins from the ER to the next Golgi station
Function of trans Golgi network ( TGN)
Sorts protein either TO the membrane or various other intracellular destination
Golgi composition
The composition of golgi is not uniform
And varies between cis and trans face
Different enzymes and different proteins
Where are most of the vescicles found
Exit sites of RER , they are also usually devoid of ribosomes
What are the 4 componenets of Golgi complex?
1- Cis - cisternae
2- medial - cistetnae ( bte cis and trans)
3- trans cisternae
4- trans Golgi network
The composition of these 4 compartments is very different from each other eg diff enzymes and proteins
Describe the movement of vescicles from ER to Golgi complex .
1- ER proteins are surrounded by a membrane to form the vescicles
2- transpprt vescicles fuse with one another and form the ERGIC ( endoplasmic reticulum golgi interediate compartement )
- vasicles move along the cytoskeleton ( microtubles )
- the vescicles fuse with golgi aparatus on the cis face and form the cis cisternae .
3- as proteinz move along - get modified by golgi specific enzymes
4- these modifications provide the signal for the final destination of the protein
Gradual movement of cisternae
Cis - cisternae Goes further and fuses to form Medial cisternae Goes further and fuses to form Trans cisternae
What are the two ways in which proteins travel through the cisternae?
1- vesicles that shuttle between its individual cisternae
2- maturation process- migration of Golgi cisternae through the stack
How proteins in vescicles move within EM
1-inward endocytic pathways (endocytosis)
2- outward secretory pathway (exocytosis)
Endocytosis ( into plasma membrane to lysosome)
Extracellular molecules are ingested in vescicle ( made from plasma membrane) and these molecules are then delivered to early endosomes and then to lysosome by late endosome
Exocytosis (from er to other organelles eg lysosomes or outside the plasma )
Protein molecules are transpprted from ER , through the golgi apparatus to the
- plasma membrane through vescicles
- to lysosome via early and late endosome - for misfolded proteins
Cytosolic and noncytosolic sides
The membrane of each compartment or vesciclr maintains its orientation
Eg - the cytosolic side of membrane always faces the cytosol and non cytosolic always faces the lume
Who is Dr randy
Randy schekman did a ground breaking research on cell membrane vescicle trafficking
Vescicle budding is deriven by ————–
Assembly of protein coat
What is the functions of protein coat
- Causes the membrane to curve and form a vescicle
- select the components to be carried by vescicle
What are the 3 main types of vesicles?
The coated Vesicles are:-
- COP I ( coat protein)
- COP II
- Clatherin
Clatherin coated - ( clatherin + adaptin 1)
Golgi to lysosome( via endosomes) and plant vacuoles
Clatherin ( clatherin+ adaptin 2)
Plasma membrane to endosomes ( endocytosis)
COP II
ER -> ERGIC -> cis Golgi -> trans Golgi
COP I
TGN -> CGN -> ERGIC -> ER
Vesicle budding and protein traffic
Buds
Transport
Thetering and docking
Fusion
Describe the formation of the Clatherin coated vesicles
- know that the outer membrane is made of clatherin
- a Clatherin coated pit forms
- self assemble into a basketlike structure on the cytosolic side
- dynamin ( GTP binding protein- a protein to which GTP and GDP binds ) covers around the ring. Dynamin and other proteins constricts the neck
- clatherin then pinches is off
What is the function of adaptins ?
Select the cargo for transport in the vesicles
Explain how adaptins select their cargo molecules in endocytosis
The cargo binds to the cargo receptor ( embedded in the membrane ) from outside the cell
Adaptin binds to the cargo receptor from inside the cell
Clatherin binds on top of the adaptin
Dynamin assembles around the forming ring , swaps GTP to GDP , and with the help of other proteins constricts the neck
Clatherin pinches the vesicles off
Once pinched off , the clatherin molecule disassemble .
Describe the transport of vesicles to the target organelles ( eg golgi )
Tethering proteins, Rab proteins , and Snare proteins direct the vesicle,es to the target proteins
1- tethering protein on the target membrane binds to the Rab protein on the vesicle
2- the vesicle docks toward target
3- t snare on target binds to the v snare
Describe the fusion of vesicle to the target .
Snare proteins catalyze the fusion
The binding of the snare proteins causes
- docking toward the target and draws the two lipid bilayers into close together
- the winding also forces any water out to allow a continuous fusion of lipid bilayer
- other proteins are recruited to help in fusion
- once done SNARES are pried apart for reuse
Further modification - glycosylation in Golgi
2 type of glycosylation occurs in golgi
1- N- linked glycoproteins
- removal of sugars added in RER
- sugars added to N of asparagine
2- O- linked glycoproteins
Adding sugars to OH core of serine or threonine.
Advantages of glycosylation
- protein more hydrophilic
- allows protein to bind to Extracellular matrix
- reduce susceptibility to proteases
- provide another level of structural complexity, giving it
- new function
- more specificity in interactions with protein.
