Protein Trafficking Flashcards
1
Q
Do proteins have the same destination after synthesis?
A
no different proteins have different destinations
2
Q
What are the prokaryotic cells?
A
inner and outer membranes
periplasmic space
secretory proteins
3
Q
What are the eukaryotic cells?
A
membrane bound compartments
secretory proteins
cytoplasm
4
Q
What are the 5 membrane bound eukaryotic compartments?
A
endoplasmic reticulum nucleus lysosomes mitochondria cell membrane
5
Q
What type of information do proteins contain?
A
information for targeting
6
Q
What type of proteins contain signals that determine their ultimate destinations?
A
nascent proteins (or newly synthesized proteins)
7
Q
What is the difference between free and RER ribosomes?
A
there is no difference!
8
Q
What determines the location of the ribosome?
A
determined by the protein being synthesized
9
Q
What 3 types of proteins are made by free ribosomes?
A
nuclear, peroxisomal, and mitochondrial proteins
10
Q
What does the nucleus have in regards to ribosomes and proteins?
A
internal nuclear localization sequences
11
Q
What does the peroxisomes have in regards to ribosomes and proteins?
A
C-terminal sequence SKF
12
Q
What does the mitochondrial matrix have in regards to ribosomes and proteins?
A
N-terminal sequence rich in positive charged amino acids and serine, threonine
13
Q
Where are long chain fatty acids processed?
A
peroxisomes
14
Q
What is SKF?
A
serine, lysine, phenylalanine
15
Q
Ribosomes bound to the endoplasmic reticulum synthesize 3 major classes of protein. What are they?
A
secretory proteins
lysosomal proteins
integral membrane proteins (excluding those of mitochondria)
16
Q
What are examples of secretory proteins?
A
proteins exported from the cell (collagen, insulin)
17
Q
What directs the ribosome to attach to the endoplasmic reticulum?
A
an N-terminal signal sequence on the nascent polypeptide
18
Q
What enzyme is used to remove the signal sequence from the secreted protein by cleavage?
A
signal peptidase
19
Q
N-terminal secretory peptide signal sequences have ________ _________
A
common features
20
Q
What are some of the common features that the N-terminal secretory peptide and signal sequences have?
A
they range in length from 13-26 residues
amino-terminal part of signal contains at least one positively charged residue
a highly hydrophobic stretch of usually 10-15 residues forms the center of the signal
residue on the amino-terminal side of the signal peptidase cleavage site usually has a small, neutral side chain (alanine common)
21
Q
Which amino acid is charged?
A
arg
22
Q
Which amino acids are hydrophobic?
A
Leu, Ala, Trp
23
Q
How does protein synthesis begin?
A
by free ribosomes binding to mRNA and commencing synthesis of N-terminal region of polypeptide
24
Q
What is the first region that is synthesized?
A
the N-terminal
25
What is the signal recognition particle (SRP)?
an RNA-protein complex that recognizes and binds to signal sequences
26
What temporarily haults translation by a ribosome?
binding of SRP
27
Where does the signal recognition particle receptor direct the peptide?
to the translocation complex
28
What does the SRP receptor do?
delivers the signal peptide (and the ribosome) to the peptide translocation complex on the cystolic face of the ER
29
What happens when SRP binds to the receptor?
it releases GDP, GTP binds in its place and SRP is released from ribosome and signal peptide threads through translocation complex
30
When SRP is released what is hydrolyzed?
GTP
31
What does signal peptidase do?
cleaves signal peptide off growing chain
32
What proteins serve as chaperones to assist correct peptide chain folding?
ATP- driven heat shock proteins
33
Once a protein enters the ER is there a way to return to the cytosol?
no once it has entered it is irreversible and cannot return to the cytosol
34
What do glycoproteins acquire in the ER?
core sugars
35
What are 2 examples of secretory proteins (mucins) that have covalently attached carbohydrate moieties?
N-linked to asparagine
| O- linked to serine, threonine
36
What do N-linked oligosaccharides have in common?
a pentasaccharide core derived by drimming a 14 residue core oligosaccharide added to specific Asn residues (Asn-X-Ser/Thr)
37
What is the carrier for N-linked glycoproteins?
dolichol phosphate
38
Where is the dolichol phosphate carrier found?
carrier molecule embedded in the ER membrane
39
What are the 3 characteristics of dolichol phosphate?
is an isoprenoid derivative
a lipid
localized to membranes
40
What is an isoprenoid?
5 carbons and then a double bond (structure)
41
How much of the core oligosaccharides are synthesized on the cystolic side of the ER?
about half
42
What things are combined to form a dolichol pyrophosphate intermediate?
nucleotide activated (UDP or GDP coupled) sugar precursors are added stepwise to the phosphate group
43
What happens to incomplete core-dolichol pyrophosphate?
it is translocated across the ER membrane into the lumen
44
What is GDP?
a carrier for manose sugars
45
2 GlcNAc + 5 mannose =
1st 7 sugars
46
What are dolichol phosphate activated sugars used for?
to complete core oligosaccaride
47
Where are oligosaccharides transferred?
to specific Asn residues in protein, releasing dolichol pyrophosphate
48
Where are activated nucleotide precursors found?
on the cytosolic side
49
Where are the activated dilichol phosphate precursors found?
on the lumen side
| 4 more mannose + 3 glucose added in ER lumen
50
Is dolichol phosphate regenerated?
yes it must be regenerated (recycled)
51
What enzyme recycles the dolichol phosphate?
phosphatase
52
What 2 drugs affect the addition of sugars?
tunicamycin
| bacitracin
53
What does tunicamycin do?
blocks the first step in oligosaccharide synthesis
54
What does bacitracin do?
blocks phosphatase that recycles dolichol phosphate
55
Why is bacitracin a very useful antibiotic?
because bacteria use a similar enzyme to recycle an isoprenoid pyrophosphate in cell wall synthesis and the enzyme is very sensitive to bacitracin
56
Where are proteins in the lumen of the ER transported?
transported to the cis side of the golgi complex by transport vesicles (transfer vesicles)
57
Where are proteins and carbohydrate moieties additionally modified?
in golgi
58
What sorts and directs the proteins to their destination?
by transfer vesicles leaving the trans face of the golgi
59
What side of the golgi is closest to the endoplasmic reticulum?
the cis side
60
What is closest to the trans side of the golgi?
the cell membrane
61
Is membrane asymmetry preserved in vesicular transport?
yes
62
What characteristic of the membrane is central to function?
membrane asymmetry
63
What corresponds to the luminal side of organelle membranes?
external face of plasma membrane
64
What does the luminal side of ER =
luminal side of golgi
65
What does the luminal side of golgi =
luminal side of transfer vesicle
66
How is phospho-N-acetyl-glucosamine added to a mannose? (which enzyme)
phosphotransferase
67
What does the phosphotransferase recognize?
the 3D motif in the protein
68
What does the phosphodiesterase remove?
N-Ac-Gln leaving mannose - 6- phosphate in core oligosaccharide
69
What does the mannose-6-phosphate and protein bind to?
receptor in golgi membrane
70
What is mannose-6-phosphate associated with?
lysosome targeting
71
What disease is due to a defect in lysosomal targeting?
I-cell disease (mucolipidosis II)
72
What enzyme is deficient in I-cell disease (mucolipidosis II)?
phosphotransferase
73
What is the default pathway out of the golgi?
secretion
74
What happens to undigested glycosaminoglycans and glycolipids?
build up as Inclusions in lysosomes
75
How many hydrolases are needed to break down glycosaminoglycans and glycolipids?
eight acid hydrolases are needed
76
Are glycosaminoglycans and glycolipids targeted to lysosomes?
no instead they are secreted
77
What does a build up as Inclusion in lysosomes cause?
severe psychomotor retardation and skeletal deformities
78
Proteins in ER lumen (ex: heat shock proteins, enzymes) will enter transport vesicles and travel where?
to the golgi
79
What is the return signal?
the carboxy-terminal sequence Lys-Asp-Glu-Leu (KDEL) on ER proteins is the return signal
80
What happens to proteins after they enter transport vesicles at the golgi?
vesicles return proteins to the ER
81
What is receptor mediated endocytosis?
a process of import of specific proteins into a cell by protein binding to receptor in plasma membrane and inclusion into vesicles
82
What is receptor mediated endocytosis used for?
delivering essential metabolites
83
What modulates response to many protein hormones and growth factors?
receptor mediated endocytosis
84
What happens to extracellular proteins?
they are targeted for destruction and taken up and delivered to lysosomes (antigen-antibody complexes by phagocytic cells)
85
What is a disadvantage to receptor mediated endocytosis?
some toxins and viruses can enter cells by this pathway
86
What is an example of a disease that is caused by disorders of receptor mediated uptake?
some forms of familial hypercholesterolemia
87
The cystosolic side of indentation has a thick coat of what type of protein?
clathrin protein
88
What are coated pits?
specialized regions of plasma membrane that contain many receptors
89
What type of proteins are most cell surface receptors?
transmembrane glycoproteins
90
What begins the invagination of coated pit?
endocytosis
91
What triggers the invagination of the coated pit?
receptor -ligand binding
92
What forms around the coated pit?
clathrin forms a lattice around the coated pit, excising it from membrane and forming coated vesicles
93
What happens to the coated vesicle?
it rapidly loses clathrin shell and fuses with an enodsome
94
What are endosomes?
larger irregular vesicles with acidic lumens
95
How are endosomes acidified?
by ATP driven proton pumps in membranes
96
What happens to the protein-receptor complexes in an acidic environment?
generally leads to dissociation of these complexes
97
What are the 4 possible fates of receptor protein pairs? (endocytosed proteins)
```
receptor protein
recycled recycled
recycled degraded
degraded degraded
transported transported
```
98
What is an example of the receptor and protein being recycled?
transferrin, MHC proteins
99
What is an example of a recycled receptor and a degraded protein?
LDL, transcobalamin II
100
What is an example of a degraded receptor and a degraded protein?
EGF, immune complexes
101
what is an example of transported receptor and a transported protein?
maternal IgG, IgA
102
What sorts the endocytosed proteins?
transferrin - transports iron from sites of absorption and storage to sites of utilization
103
How is transferrin formed?
two Fe3+ ions bind/apotransferrin molecule = transferrin (aka ferrotransferrin)
104
What binds to the receptor in coated pits?
transferrin but not apotransferrin
105
Why is iron closely guarded?
because it can become a method of free radical generation
106
What is bound to iron when transferring through the bloodstream?
transferrin
107
How is transferrin processed?
the endosome acidifies, Fe3+ dissociates from apotransferrin which remains bound to receptor
108
What is internalized into the endosome?
transferrin (transferrin processing slide)
109
What happens to the receptor that was bound to apotransferrin?
it is recycled
110
What s ferritin?
a storage form of iron (ferritin picks remaining iron in cytosol)
111
What happens to the part of vesicle with apotransferrin bound to its receptor?
pinches off and is directed to the plasma membrane
112
What happens when the vesicle is pinched off?
it fuses with membrane
113
What happens when the vesicle fuses with the membrane?
a sudden shift in PH releases apotransferrin from receptor
114
What do membrane-enveloped viruses do to enter cells?
exploit endocytic pathways
115
What is Semliki virus and how is it obtained?
related to yellow fever
enters susceptible cells by binding to receptors in coated pits and is endocytosed
the pH change in endosome triggers release of viral nucleocapsid from the membrane
116
How does diphtheria toxin enter cells?
by binding to growth factor receptor cells
| (Internalized by endocytosis)
117
How are proteins turned over?
by ubiquitin tags (signal for destruction)
118
The C-terminal of ubiquitin attaches to what of the target protein?
lysine -NH2
119
Which end is more stable due to the signal for ubiquitinylation?
N-terminal amino acid is more stable because the ubiquitin attaches at the C- terminal
120
What proteins are poorly ubiquitinylated?
Gly,Ala,Cys,Met
121
What are the 4 unstable proteins? (rapidly ubiquitinylated)
Arg, His, Ile, Leu
