ER and secretory pathway

Question 1

what is the rough ER for?

Answer 1

synthesis of proteins and glycosylation.

Question 2

what are resident proteins?

Answer 2

→proteins that are manufactured in the ER and stay in the ER.

Question 3

how do they stay in the ER?

Answer 3

→they have a retention signal which allows them not to be transported out.

Question 4

what does BiP do?

Answer 4

→identifies proteins that have been improperly made and keeps them from going to their final destinations.

Question 5

what is calcium sequestration?

Answer 5

→storage of Ca2+ ions inside the lumen of the ER.

Question 6

what do the P450 enzymes do?

Answer 6

→they play a role in detoxification and transform the inactive form of the drug into the active form.
→this occurs in the ER of liver cells.

Question 7

why do secreted proteins differ from resident proteins?

Answer 7

→they have a signal sequence at the 5’ end which is rich in hydrophobic amino acids

Question 8

what is the difference between free and bound ribosomes?

Answer 8

→free ribosomes are in the cytosol and translate soluble proteins for release into the cytoplasm.

→bound ribosomes translate proteins which are secreted or incorporated into membranes of lysosomes.

Question 9

what are the steps fo co-translational protein targeting to the ER?

Answer 9

→translation begins at a ribosome that is free in the nucleus

→when the signal sequence emerges from the ribosome, the SRP interacts with it and guides it to an SRP receptor in the membrane of the ER.

→the SRP helps dock the ribosome onto a translocon so the ribosome becomes part of the ER.

→once the ribosome is attached translation continues and the PP chain passes into the ER while the signal sequence remains bound to the channel.

Question 10

what does the signal sequence determine?

Answer 10

→whether the ribosome that is translated is free or bound.

Question 11

how does insulin get modified?

Answer 11

→when insulin gets secreted it is called preproinsulin and has a signal sequence guiding it to a translocon.

→the signal sequence gets cleaved off and after that it is called proinsulin.

Question 12

what happens to faulty proteins ?

Answer 12

they are degraded and are not released

Question 13

what are the three different domains of the golgi?

Answer 13

→the CIS face, the medial golgi and the TRANS face

Question 14

what do glycosidases do?

Answer 14

catalyze the hydrolysis of glycosidic bonds in complex sugars.

Question 15

what do sulfatases do?

Answer 15

they remove sulfate groups

Question 16

where are sphingolipids synthesized?

Answer 16

in the golgi

Question 17

what are functions of the ER

Answer 17

→protein synthesis
→glycosylation 
→folding and assembly and multi-protein complexes
→Lipid synthesis
→Ca2+  sequestration 
→Detoxification by P450 enzymes

Question 18

what are the protein modifications that occur in the ER?

Answer 18

→proteolysis (breakdown of proteins into smaller polypeptides)
→ disulfide bond formation
→glycosylation
→ deglycosylation
→ protein folding and assembly (tertiary and quaternary structure)

Question 19

describe the structure of the ER

Answer 19

continuous network of membrane tubules that is continuous with the nuclear envelope.

Question 20

what is the function of the golgi?

Answer 20

→PROTEIN MODIFICATION: glycosidases, sulfatases, proteases, O-linked glycosylation, glycosyltransferases -

LIPID SYNTHESIS: sphingomyelin, glucosylceramide

PROTEIN AND LIPID SORTING TO: secretory, granules, plasma membrane, basolateral vs apical membrane, endosomes, lysosomes

Question 21

what do glycosyltransferases do?

Answer 21

catalyze the formation of the glycosidic linkage to form a glycoside.