8- Membrane Trafficking

Question 1

What modifications do proteins undergo in the ER lumen

Answer 1

Folding
o Formationofdisulphidebonds 
o Glycosylation
o Specificproteolyticcleavages
o Assemblyofmultimericproteins

Question 2

What causes CF

Answer 2

deletion of three nucleotides at the 508th postion of the protein, losing a critical phenylalanine residue which causes the protein to not fold properly, so it is retained and degraded in the ER. Thus the symptoms of cystic fibrosis occur as there is no functional protein

Question 3

What is Robinow syndrome

Answer 3

mutation in a cell surface tyrosine kinase receptor (ROR2), which is responsible for cartilage and bone growth. A mutation causes retention and degradation in the ER, causing dysmorphic facial appearance, dwarfism, vertebral malformations, congenital heart defects and genital hypoplasia

Question 4

Name of disease of the endocytotic pathway

Answer 4

Familial hypercholesterolaemia

Question 5

What are the 3 types on endocytosis

Answer 5

Receptormediatedendocytosis
o Pinocytosis(nonspecificfluidphase)
o Macropinocytosis/phagocytosis(fluid/particlese.g.microbes

Question 6

What happens to material taken up by endocytosis

Answer 6

Material taken up is either recycled (as with the LDL receptor – endocytic vesicles), degraded (taken to the lysosome – late endosomes and lysosomes) or transcytosed (early and late endosomes)

Question 7

Where are disulphide bonds formed

Answer 7

Disulphide bonds are formed in the endoplasmic reticulum (ER) not the Golgi.

Question 8

How is mannose targeted by lysosomes

Answer 8

It is the sugar mannose that gets phosphorylated at position 6 allowing these tagged proteins to be recognized by the mannose-6-phosphate receptor and thereby targeted to lysosomes. I-cell (inclusions) disease results from mutations in the phosphotransferase enzyme which catalyses this reaction and targets lysosomal enzymes such as lysosomal hydrolase to the lysosome.

Question 9

What is robinow syndrome

Answer 9

The disease known as Robinow Syndrome, which is characterized by a dysmorphic facial appearance and vertebral malformations, results from defects in the trafficking of the tyrosine kinase receptor ROR2 to the cell surface. Misfolded ROR2 protein is retained in the endoplasmic reticulum (ER).

Question 10

What is the molecule dynamin involved in

Answer 10

pinching off” the vesicle from the membrane in a GTP-dependent process.