1.9 Protein Trafficking & Targeting

Question 1

Proteins to be translocated contain _____ that help direct them to their proper location. What are these structures composed of?

Answer 1

tags

specific amino acid sequences

Question 2

______ bind the tag sequence and direct the protein to their destination

Answer 2

chaperone

Question 3

additional proteins form _____ (______) to allow translocation of proteins into membrane bound organelles

Answer 3

pores (translocon)

Question 4

how many tags can a protein have?

Answer 4

multiple if need to go multiple locations

Question 5

where does all protein translation begin?

Answer 5

cytosol (except for 13 mitochondrial proteins)

Question 6

if all protein translation begins in the cytosol, do they end there as well?

Answer 6

no

Question 7

what structures does the secretory pathway consist of? what is system called?

Answer 7

ER, Golgi apparatus, lysosomes, endosomes, and secretory vesicles

endomembrane system

Question 8

what is the function of secretory pathway?

Answer 8

processing of proteins for export from the cell, proteins destined for the plasma membrane, lysosomes, vacuoles, etc

Question 9

what is the first step for proteins entering the secretory pathway?

Answer 9

target the ER

Question 10

what is the next step in secretory pathway after proteins enter the ER?

Answer 10

carried by vesicle transport to other compartments of system. highly regulated

Question 11

in secretory pathway, the proteins targeted to the ER require a ______ or ______

Answer 11

tag or targeting signal (signal sequence or signal peptide)

Question 12

the tag, or targeting signal required by proteins to be sent to ER is encoded within where?

Answer 12

the N-terminal portion of the protein

Question 12

the tag, or targeting signal required by proteins to be sent to ER is encoded within where?

Answer 12

the N-terminal portion of the protein

Question 13

proteins that do not have a signal peptide stay where for the rest of translation?

Answer 13

in the cytosol

Question 14

the signal sequence for proteins targeted to ER in secretory pathway, is recognized by what?

Answer 14

signal recognition particle (SRP)

Question 15

what does the SRP do?

Answer 15

in the secretory pathway, is directs the ribosome to a specific receptor on the ER. this signal sequence also prevents the ribosome from continuing translation in the cytosol.

Question 16

what removes the signal sequence on the protein after it is successfully moved into the ER? what does this allow the protein to do?

Answer 16

signal peptidase

it releases the peptide which folds into its correct shape

Question 17

what enzyme adds sugars to protein during translation

Answer 17

glycosyltransferase

Question 18

what are the first to events that occur when proteins get moved to the ER lumen?

Answer 18

1. signal peptidase removes signal sequence

2. gylcosyltransferase adds sugars during translation

Question 19

proteins destined to remain in ER membrane have an amino acid tag that determines this location called _____

Answer 19

stop transfer sequence (STA)

Question 20

explain the structure, function, and process of STA in the ER membrane?

Answer 20

22-25 hydrophobic amino acid sequence in the middle of the protein that forms an alpha helix

when encountered it gets moved into the membrane, then translation of the rest of the protein continues in cytosol

Question 21

what things are required in order to assist proper protein folding and release from the ER?

Answer 21

1. molecular chaperones

2. folding enzymes

Question 22

what types of bonds are formed and rearranged in the ER?

Answer 22

Disulfide bonds

Question 23

what happens to terminally misfolded proteins in the ER?

Answer 23

they are degraded in the cytosol

Question 24

proteins that fail to fold or assemble properly in the ER are subjected to a process known as…

Answer 24

ER-associated degradation (ERAD)

Question 25

what is the ERAD process?

Answer 25

identifying, reverse translocating (back to the cytosol) and degrading misfolded ER proteins

Question 26

what happens to the proteins in the cytosol after ERAD?

Answer 26

in the cytosol, these misfolded proteins are ubiquitinated and subsequently degraded by proteasomes

Question 27

what is glycosylation?

Answer 27

a carbohydrate is covalently attached to a target macromolecule (typically proteins or lipids) to produce glycoproteins and glycolipids

Question 28

the sequence of sugars in oligosaccharides are highly _____

Answer 28

specific

Question 29

why glycosylate proteins?

Answer 29

glycosylation may assist in folding, transport, stability, recognition, and have regulatory roles

Question 30

Oligosaccharides can be added to a protein through an _______ (__-linked).
Where does this occur?

Answer 30

asparagine (N-linked)

ER and Golgi

Question 31

what is significant about glycosylation and its timing?

Answer 31

even tho glycosylation is considered a ‘post-translational modification’ it is actually performed during translation in the ER

Question 32

where does the biosynthesis of oligosaccharide to be N-linked to a protein begin?

Answer 32

cytosol