protein sorting and trafficking 8

Question 1

How is cargo selected?

Answer 1

• Active recruitment
• selective exclusion
• passive inclusion

Question 2

What is a RAN protein in the ER membrane ?

Answer 2

Ran (RAs-related Nuclear protein) also known as GTP-binding nuclear protein Ran is a protein that in humans is encoded by the RAN gene.

Question 3

What happens when the RAN - Gef is activated?

Answer 3

Loaded with GTP, GDP remove

Question 4

What does Gef stand for?

Answer 4

Guanine nucleotide exchange factor

Question 5

What happens when the SAR1 - GTP protein is activated?

Answer 5

conformational change of the SAR1 protein and you get and insertion of the amphipathic helix into the ER

Question 6

What is the role of lumen proteins in selecting cargo?

Answer 6

• selectively recruit cargo into buds by interacting with cargo receptors , these span the ER membrane and interact with coat proteins

Question 7

How are the cargo and coat linked

Answer 7

via protein - protein interactions

Question 8

How are some proteins excluded from entering the buds?

Answer 8

• some are excluded fro mentoring budding vesicles due to mis folding
• some proteins are passively included in the vesicle , these will be returned to the ER

Question 9

What can the ER be referred to as?

Answer 9

‘quality control station’ .

- Antibodies do not get packaged into the ER transport vesicles until they are fully assembled with al 4 of the chains

Question 10

What is the KDEL sequence?

Answer 10

Lysine, Aspartic acid, Glutamic acid, Leucine = KDEL in one letter amino acid code

Question 11

Why is the KDEL sequence significant?

Answer 11

If these proteins leave the ER and get trafficked to the Golgi, they can be retrieved from the Golgi in COPI vesicles.
KDEL containing proteins are recognised by KDEL receptors (transmembrane protein) and selectively packaged into COPI coated vesicles for retrograde traffick back to the ER.

Question 12

Where does the COP2 coat work on?

Answer 12

Transferring cargo from the ER to the Golgi

Question 13

Where does the COP1 coat work on?

Answer 13

Transferring cargo from t Golgi to the Endoplasmic reticulum

Question 14

What proteins are used to target specific membranes?

Answer 14

• Rab proteins ( small GTP binding proteins) and SNARE proteins

Question 15

How do SNARE proteins work/

Answer 15

• brings two membranes close together and forces them to bring.

Question 16

What are the two types of SNARE protein?

Answer 16

• V - SNARE

- T - SNARE

Question 17

What happens when the two membranes fuse?

Answer 17

• water is squeezed out

- have hemifusion intermediates

Question 18

Which proteinns get sugars added to them and where?

Answer 18

• Non - cytosolic proteins

- get added in the lumen of the ER

Question 19

What are NXS/T sequences?

Answer 19

A recognised sequence in which a sugar molecule is added

Question 20

Where is oligosaccharyl transferase situated and what does it do?

Answer 20

• transfers the oligosaccharide from the lipid to the protein
• this transfer occurs in the lumen of the ER. Cytoplasmic proteins do not get glycosylated even if they have an NXS/T sequence in them.

Question 21

What do chaperones do?

Answer 21

• Prevents misfiled/ unassembled proteins from leaving the ER

Question 22

How is the Golgi apparatus arranged?

Answer 22

• in cistern, transport from cis- trans sides

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Question 23

Where are disulphide bonds formed?

Answer 23

In the ER. Proteins in the cytoplasm do not have disulphide bonds

Question 24

why does the Golgi have many cisternae?

Answer 24

• different compartments contain different enzymes to modify proteins and lipids

Question 25

What is the route for enzymes getting into the lysosomes?

Answer 25

• proteins produced in the ER, then Golgi then they go through endozyomes then to lysosomes

Question 26

How does LDL enter the cell and how is it destroyed?

Answer 26

LDL receptor is trafficked to the cell surface from the ER. The receptor recycles between the plasma membrane and endosomes picking up LDL (low density lipoprotein) at the PM and releasing it in endosomes (acidic pH). LDL is trafficked to lysosomes. The receptor returns to the PM.