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cell and molecular > 7.10-7.20 > Flashcards

7.10-7.20 Flashcards

1
Q

what happens once hydrophobic anchor sequences emerge from the ribosome

A

recognized and are transferred out of the translocon into the bilayer

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2
Q

some hydrophobic sequences are what?

A

both dual purpose and anchor sequences

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3
Q

when is the N-terminal signal likely cleaved

A

after the beginning of translocation

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4
Q

signal anchor proteins target by what?

A

using an internal transmembrane domain (signal anchor)

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5
Q

what decides whether the N-terminal or C-terminal is translocated into the ER

A

distribution of charged residues on either side of the transmembrane domain

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6
Q

polytopic proteins

A

proteins that span the membrane multiple times

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7
Q

polytopic proteins can have transmembrane regions that integrate __________ or in _______

A

one at a time or in pairs

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8
Q

what happens if the ER-signal peptide is N-terminal?

A

it is almost always cleaved after it has served its purpose

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9
Q

signal peptidase complex composition

A

5 subunits: 2 with proteolytic activity and 3 regulatory

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10
Q

what is the exact cleavage site influenced by

A

aa residues in immediate vicinity of cleavage site

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11
Q

what is the signal peptide often processed with after removal

A

signal peptide petidase

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12
Q

IMPs

A

integral membrane proteins, non-removable from the membrane by a salt extraction procedure

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13
Q

GPI-anchoring always tethers a protein to the ___________ face of a membrane

A

non-c

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14
Q

what does GPI stand for

A

glycosylphosphatidylinositol

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15
Q

what is a glycosylphosphatidylinositol

A

PI that has sugars added to it

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16
Q

which side does GPI-anchoring begin on

A

c-face of ER membrane

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17
Q

how does initial GPI get from c-face to non-c-face

A

flippase/translocase moes it across to the lumen sdie

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18
Q

what happens once the GPI is moved to the lumen side

A

more sugars are added along with three phosphoethanolamines

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19
Q

signal for GPI-anchoring

A

small C-terminal hydrophobic domain of variable length

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20
Q

what is the GPI-anchoring signal recognized by

A

integral membrane complex which cuts the signal off from the protein (was in process of being translocated)

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21
Q

omega site

A

new C-terminus to which integral membrane complex is attached

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22
Q

what does the integral membrane complex attach omega site to

A

terminal phosphoethanolamine residue of GPI, enzyme complex liberates itself
- (2-step transamidation reaction)

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23
Q

purpose of GPI-anchoring

A
  • way of targeting proteins in polarized cells/lipid rafts
  • would give IMP more lateral mobility
  • free protein from membrane association by enzymatic cleavage of attachment, passing message to interior of cell
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24
Q

more than half of secretory and membrane proteins in a cell are ___________

A

glycosylated

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25
glycosylation in ER is termed what?
N-linked
26
why is glycosylation in ER is termed N-linked
sugars are attached to asparagine residues
27
oligosaccharyltransferase
transfers oligosaccharide en bloc onto translocating protein
28
where was the oligosaccharide first synthesized
pre-synthesized beginning in cytosol, with minor membrane phospholipid dolichol-phosphate
29
where are sugars added during glycosylation
to dolichol-P - then flippase moves it to the lumen-face of the membrane, and more sugars are added
30
where do removal of some sugar residues occur after oligosaccharide addition
in ER and Golgi apparatus
31
most abundant protein in the ER lumen
BiP
32
description of BiP
chaperoning, member of hsp70 family
33
what does BiP bind to
exposed hydrophobic patches
34
where are hydrophobic patches in a protein normally found
buried within globular protein
35
does the cytosol have an oxidizing or reducing environment
reducing
36
true or false: disulfide bonds form in cytosol
false
37
does the ER lumen and ECM have an oxidizing or reducing environment
oxidizing
38
true or false: disulfide bonds form readily in the ER lumen and ECM
true
39
what are disulfide bonds catalyzed by
protein disulfide isomerases
40
what does PDI catalyze
disulfide bond rearrangements and formation
41
PDI is ____________ when it ___________ the cysteines in a translocating protein to help it fold
reduces, oxidizes
42
what does PDI oxidize
cysteines in translocating protein
43
how is PDI re-oxidized
ER protein EroP1 oxidizes PDI by being itself reduced
44
what is EroPI oxidized by
FAD
45
what is a lectin
protein that binds specifically to sugar residues
46
2 mains types of lectin
1. calnexin 2. calreticulin
47
calnexin
IMP in ER membrane
48
calreticulin
ER-lumenal protein
49
purpose of calnexin or calreticulin activity in
QC - to make sure certain proteins are properly folded before they are allowed to leave the ER
50
ticket to enter calnexin cycle
have to be N-glycosylated
51
what happens after entering calnexin cycle
2 distal glucose residues are quickly removed by glucosidase I and II
52
what happens after 2 distal glucose residues removed
calnexin associates and helps contact ERp57 to catalyze disulfide bond formation/rearrangment and allows folding/refolding
53
ERp57
chaperonin and PDI family member
54
what happens if a protein isn't folded properly
glucose is re-added by UGGT, which allows it to Reb ind to calnexin and repeat the cycle
55
UGGT
UDP-glucose-glycoprotein-glycosyl transferase
56
how does UGGT know that a protein isn't folded
exposed clusters of hydrophobic residues
57
proteins in the secretory pathway whose structure depends on the assembly of subunits are retained in the ER by what?
chaperone-association until that assembly is completed
58
oligomerization
formation of complexes
59
various retention mechanisms
- associating subunit with BiP - an exposed cysteine binding to a PDI - exposed ER retention signal that will be masked later
60

cell and molecular (21 decks)

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