Question

QUESTION 7

Proteins in a secretory pathway _______________.

		are usually glycosylated in the lumens of the endoplasmic reticulum (ER) and Golgi
		are usually glycosylated only in the Golgi apparatus
		are synthesized and completely folded in the cytosol and then translocated into the ER
		do not pass through endosomes, which are only part of endocytic pathways

QUESTION 8

1. In a regulated secretory pathway ____________________.

   		a product is not packaged into vesicles until a signal is received
   		a product is packaged into vesicles that are continually trafficked to the plasma membrane and fuse with it until a signal is received, at which point secretion stops
   		a core oligosaccharide is not transferred from a lipid to a polypeptide in the endoplasmic reticulum until a signal is received
   		a product is packaged into vesicles that do not fuse with the plasma membrane until a signal is received

QUESTION 9

1. A plasma membrane protein with an odd number of transmembrane alpha helices could have had ____________________.

   		No N-terminal signal and an equal number of start- and stop-transfer signals in its amino acid sequence
   		1 more start-transfer signal than stop-transfer signals in its amino acid sequence
   		a single N-terminal signal and no stop-transfer signals in its amino acid sequence
   		only stop-transfer signals and no start-transfer signals in its amino acid sequence

Answer 1

7. proteins in a secretory pathway are usually glycosylated in the lumens of Endoplasmic reticulum and golgi. There may be O linked or N linked glycosylation. In N linked glycosylation a 14 residue precursur of glycoproteins are attached to the protein followed by processing. There are glycosyltransferases which catalyze these reactrions.

8. In a regulated secretory pathway a product is packaged into vesicles but do not fuse with the plasma membrane until a signal is received. This pathway is mainly followed by hormones or neurotransmittors which require regulated secretion.

9. A plasma membrane protein with an odd number of transmembrane alpha helices could have had 1 more start-transfer signal than stop-transfer signals in its amino acid sequence. Examples of this include G protein coupled receptors with 7 transmembrane helices where 4 start transfer and 3 stop transfer signals are present.