Membrane Proteins and the Secretory Pathway

Question 1

four types of membrane proteins

Answer 1

transmembrane, monolayer-associated, lipid-linked, protein-attached

Question 2

Type I topology

Answer 2

single pass protein anchroed to the lipid membrane with a stop transfer anchro sequence, have their N-terminus targeted to the ER lumen

Question 3

Type II topology

Answer 3

single pass protein anchored with a single-anchor sequence and hte carboxyl terminus in the ER lumen

Question 4

Type III topology

Answer 4

single pass protein with a signal-anchor sequence and the amino terminus in the ER lumen

Question 5

Type IV topology

Answer 5

multi-pass protein, amino terminus on either side

Question 6

glycosylphosphatidylinositol (GPI) anchor

Answer 6

modified lipid in cell membrane that cells adhere to

some type I proteins exchange their carboxyl terminal transmembrane segment for a GPI anchor

Question 7

Describe the directions of vesicular traffic in cells.

Answer 7

Question 8

protein transport into ER

Answer 8

signal recognition particle (SRP) recognizes signal sequence and brings it to receptor in the ER membrane

protein goes through channel, and signal is eventually cleaved by a signal peptidase

Question 9

What are some different ways to orient proteins based on signal sequence?

Answer 9

Question 10

N-linked glycosylation

Answer 10

the process of adding sugar molecules onto all proteins in the ER membrane, same sugars

important for protein stability

Question 11

BiP

Answer 11

one of many ATP-dependent chaperones that assist folding as the protien emerges from the translocon

Question 12

Calnexin

Answer 12

calcium binding protein that monitors that folding of glycoproteins

binds to oligosaccharides and “senses” when the protein is correctly folded

Question 13

mannosidases

Answer 13

trim mannose residues from the oligosaccharide, function similarly to calnexin to ensure proper folding

Question 14

protein disulfide isomerases (PDIs)

Answer 14

catalyze formation of disulfide bonds

Question 15

ERP57

Answer 15

chaperone protein that works with calnexin to ensure proper folding of proteins using the trimming of the oligosaccharides as a guide

Question 16

SEL1

Answer 16

protein in the ER that pushes improperly folded proteins out as a single chain, which is then polyubiquitinylated and degraded

Question 17

PERK

Answer 17

protein kinase that phosphorylates eIF2alpha, which blocks translation

ATF4 can escape the transtion block so it goes to the nucleus and activates a stress response

Question 18

ATF6

Answer 18

released from the ER membrane by high levels of BiP, and goes through the golgi to get cleaved and become a transcription factor to activate stress genes

Question 19

IRE1

Answer 19

BiP interaction activates a unique splicing mechanism, causes intron mechanism for XBP1 to be inactivated, creating a transcription factor to activate a stress response

also responsible for triggering autophagy or apoptosis through activation of Jun Kinase

Question 20

unfolded protein response

Answer 20

a collection of several mechanisms the cell can undergo to deal with unfolded proteins

uses BiP as a sensor

Question 21

ER-associated degradation (ERAD)

Answer 21

a process of degradation that proteins undergo if proteins cannot fold properly or take too long to fold in the ER, uses SEL1 to unfold proteins and mark for degradation

Question 22

functions of the cis golgi network

Answer 22

sorting, phosphorylation of oligosaccharides on lysosomal proteins

Question 23

functions of the cis cisterna of golgi

Answer 23

removal of mannose

Question 24

function of mdial cisterna of golgi

Answer 24

removal of mannose and addition of N-acetyl-glucose (GlcNac)

Question 25

trans cisterna

Answer 25

addition of galactose and NANA

Question 26

trans golgi network

Answer 26

sulfation of tyrosines and carbohydrates, prepare for vesicular transport

Question 27

Describe the vesicular transport from the Golgi.

Answer 27

Question 28

packaging of cargo in the Golgi

Answer 28

need coat complex II (COPII)

recruitment of cargo proteins and coat machinery

formation of vesicle that pinches off

Question 29

vesicle compartment topology

Answer 29

lumenal aspect of the ER correlates to the outside of the cell once the transport completes

Question 30

recycling of components

Answer 30

uses coat complex COPI and peptide sequences often have a KDEL motif that directs ER proteins form the GOlgi to recyling

Question 31

mannose-6-phosphate receptors

Answer 31

integral membrane proteins that bind lumenal lysosomal hydrolases, causes formation of clathrin coated vesicles

marked for transport to early or late endosomes, which become lysosomes

Question 32

exosomes

Answer 32

small vesicles released from the plasma membrane

have roles in coagulation, intercellular signaling, and waste management

generated in multivesicular endosomes

can possible shuttle ncRNAs to other cells for signaling and regulation

Question 33

three types of endocytosis

Answer 33

phagocytosis, pinocytosis, receptor-mediated endocytosis

Question 34

pinocytosis

Answer 34

ingestion of small bits of the plasma membrane with extracellular fluid

small vesicles c alled caveolae

Question 35

phagocytosis

Answer 35

ingestion of large parthicles and delivery to lysosomes

requires the actin cytoskeleton

Question 36

receptor-mediated endocytosis

Answer 36

responsible for uptake of essential nutrients such as iron and cholesterol

used to recycle and down-regulate receptors

uses clathrin coat and adaptin molecules along with the specific receptors

Question 37

endosomes

Answer 37

come from endocytosed vesicles that fuse with each other, early and late endosomes, eventually becomes lysosomes and contents are degraded

Question 38

two types of autophagy

Answer 38

microautophagy and macroautophagy

operates to recycle cellular components, active under startvation conditions

Question 39

microautophagy

Answer 39

occurs by the capture of small volumes of cytoplasm by invagination of the membranes in multivesicular bodies and lysosomes

cytoplasmic components are hydrolyzed within the lysosomes

Question 40

macroautophagy

Answer 40

involves the engulfment of large volumes of cytoplasm including glycogen granules, ribosomes, and organelles

Question 41

autophagic vacuole

Answer 41

forms when flattened sheets of membranes derived from the smooth ER coalesce to form a double membrane vesicle

fusion with lysosomes forms an autolysosome, where engulfed contents are degraded

Question 42

two types of secretion

Answer 42

constitutive secretion - simply move materials out of the cell in regular intervals, both soluble and membrane associated proteins

regulated membrane fusion - take secretory vesicles and accumulate them near the plasma membrane, only allow them to fuse with the plasma membrane when stimulated with a signal, electrical activity, etc.

Question 43

three fates of internalized receptors

Answer 43

recycled, degraded, transcytosed

Question 44

Descrube the sorting of proteins from the trans golgi network to the lysosome.

Answer 44

indirect and direct pathways

indirect goes from golgi to membrane, which can then be engulfed and degraded

direct goes to late endosome and then lysosome or goes directly to lysosome

Question 45

Describe the composition of the lysosome.

Answer 45

Question 46

sorting of plasma membrane proteins in polarized cells

Answer 46

direct sorting - goes from Golgi to the right surface of the cell

indirect sorting - goes from golgi to basolateral surface and then sorted from there through early endosomes