Lecture 17 Part 2 - Golgi Apparatus And Vescicular Transport

Question 1

State the characteristics of Golgi complex

Answer 1

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

Question 2

Polarity of golgi complex

Answer 2

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

Question 3

Functions of golgi

Answer 3

• 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

Question 4

Golgi is named after

Answer 4

Camillo golgi

Question 5

Which cell doesn’t have Golgi

Answer 5

RBC

Question 6

Function of receiving end of golgi ( CGN )

Answer 6

Sorts proteins from the ER to the next Golgi station

Question 7

Function of trans Golgi network ( TGN)

Answer 7

Sorts protein either TO the membrane or various other intracellular destination

Question 8

Golgi composition

Answer 8

The composition of golgi is not uniform
And varies between cis and trans face
Different enzymes and different proteins

Question 9

Where are most of the vescicles found

Answer 9

Exit sites of RER , they are also usually devoid of ribosomes

Question 10

What are the 4 componenets of Golgi complex?

Answer 10

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

Question 11

Describe the movement of vescicles from ER to Golgi complex .

Answer 11

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

Question 12

Gradual movement of cisternae

Answer 12

Cis - cisternae
Goes further and fuses to form
Medial cisternae
Goes further and fuses to form
Trans cisternae

Question 13

What are the two ways in which proteins travel through the cisternae?

Answer 13

1- vesicles that shuttle between its individual cisternae

2- maturation process- migration of Golgi cisternae through the stack

Question 14

How proteins in vescicles move within EM

Answer 14

1-inward endocytic pathways (endocytosis)

2- outward secretory pathway (exocytosis)

Question 15

Endocytosis ( into plasma membrane to lysosome)

Answer 15

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

Question 16

Exocytosis (from er to other organelles eg lysosomes or outside the plasma )

Answer 16

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

Question 17

Cytosolic and noncytosolic sides

Answer 17

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

Question 18

Who is Dr randy

Answer 18

Randy schekman did a ground breaking research on cell membrane vescicle trafficking

Question 19

Vescicle budding is deriven by ————–

Answer 19

Assembly of protein coat

Question 20

What is the functions of protein coat

Answer 20

• Causes the membrane to curve and form a vescicle

- select the components to be carried by vescicle

Question 21

What are the 3 main types of vesicles?

Answer 21

The coated Vesicles are:-

• COP I ( coat protein)
• COP II
• Clatherin

Question 22

Clatherin coated - ( clatherin + adaptin 1)

Answer 22

Golgi to lysosome( via endosomes) and plant vacuoles

Question 23

Clatherin ( clatherin+ adaptin 2)

Answer 23

Plasma membrane to endosomes ( endocytosis)

Question 24

COP II

Answer 24

ER -> ERGIC -> cis Golgi -> trans Golgi

Question 25

COP I

Answer 25

TGN -> CGN -> ERGIC -> ER

Question 26

Vesicle budding and protein traffic

Answer 26

Buds
Transport
Thetering and docking
Fusion

Question 27

Describe the formation of the Clatherin coated vesicles

Answer 27

• 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

Question 28

What is the function of adaptins ?

Answer 28

Select the cargo for transport in the vesicles

Question 29

Explain how adaptins select their cargo molecules in endocytosis

Answer 29

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 .

Question 30

Describe the transport of vesicles to the target organelles ( eg golgi )

Answer 30

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

Question 31

Describe the fusion of vesicle to the target .

Answer 31

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

Question 32

Further modification - glycosylation in Golgi

Answer 32

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.

Question 33

Advantages of glycosylation

Answer 33

• 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.