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63 Cards in this Set
- Front
- Back
Which end of the peptide emerging from the ribosome contains the RER target sequence? |
N' end |
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In the signal hypothesis, how does the peptide get into the RER? (6 steps) |
1. SRP: signal recognition particle binds to signal sequence of peptide and stalls translation 2. SRP binds SRP receptor in RER membrane, which is associated with a translocon 3. Binding of SRP to R mediates GTP binding 4. GTP hydrolysis opens translocon 5. SRP dissociates from ER R and ribosome 6. Peptide is translated through translocon |
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What helps to push the growing peptide chain through the translocon pore from the cytosolic side? |
ATP hydrolysis during translational elongation |
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What helps to push the growing peptide chain through the translocon pore from the ER lumen side? |
BiP Sec63 complex |
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What causes BiP to have a conformational change, binding peptide and racketing it through the translocon? |
Binding & hydrolysis of ATP |
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In which type of membrane insertion is the signal cleaved? |
Type I |
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In which types of membrane insertion is the C' end facing the cytosol? |
Types I and III |
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How can proteins be anchored in the cytosolic side of the ER membrane? |
GPI linkage GlycosylPhosphatidylInositol linkage |
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On which side of the membrane are GIP-linked proteins linked? |
ER lumen, Extracellular leaflet
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What is the process of anchoring a single pass protein in the membrane? |
1. N' signal cleaved 2. Stop Transfer Anchor Sequence of hydrophobic AAs 3. Lateral peptide movement through translocon until STA is inside membrane 4. Remaining peptide is synthesized in cytosol |
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The ++++ charged AAs next to the signal anchor sequence end up on which side of the ER membrane? |
Cytosolic side |
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What is the anchor of a GPI-linked protein in the membrane? What is the end of the linker? Which end of the protein is linked to the GPI-anchor? |
Anchor: PI End: phosphoethanolamine C' end of protein is linked |
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What enzyme is essential for creating GPI-anchors, cleaves proteins on the ER lumen side to attach the new C' to the anchor? |
GPI-transamidase |
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What are 2 types of protein modifications that occur in the ER? |
1. Glycosylation 2. Disulfide bonds |
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What are carbohydrate-binding proteins that can interact with other glycosylated proteins? Examples? (2) |
Lectins ie Calnexin and Calreticulum |
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What is the enzymatic addition of carbs to proteins? The non-enzymatic addition? |
Glycosylation Glycation |
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In O-linked glycosylation: carbs are added to... |
-OH groups of serine and threonine |
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In N-linked glycosylation: carbs are added to.... |
asparagine |
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What enzyme is involved in O-linked glycosylation? In N-linked glycosylation? |
Glycosyl transferase Oligosaccharyl transferase |
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In N-linked glycosylation, glycans are added __________, in O-linked, glycans are added __________ |
N: as a preformed complex O: sequentially (one at a time) |
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What is an example of O-linked glycosylation? |
ABO blood groups |
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What is the consensus sequence in N-linked glycosylation? |
Asn-X-Ser/Thr |
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What is the backbone of the oligosaccharide complex that is used in N-glycosylation? |
Dolichol phosphate |
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What is the first reaction in synthesis of the oligosaccharide complex that is used in N-glycosylation? What inhibits this? |
UDP-GluNAc -> UMP GluNAc phosphate is added to dolichol phosphate Inhibits: tunicamycin |
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In what form are sugar residues added to the oligosaccharide (for N-glycosylation) |
Activated NT-sugar donors (UDP-sugar or GDP-sugar) |
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How is an N-glycosylation processed before the protein is ready for transfer to the Golgi? |
3 glucose and 1 mannose are removed |
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Disulfide bonds are only found in which types of proteins? |
Secreted proteins or those in extracellular leaflet of plasma membrane |
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What enzyme helps to produce disulfide bonds or rearrange them? |
PDI (Protein Disulfide Isomerase) |
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What enzyme helps restore PDI to its oxidized/disulfide bonded form? |
Ero1 |
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What protein deficiency causes liver disease in children and emphysema in adults? What is the specific problem with that protein? |
alpha-1 antitrypsin A point mutation prevents proper folding |
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Anterograde proteins are which type of vesicle? What coat proteins? What GTPase? |
COPII Sec coat Sar1 GTPase |
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Retrograde vesicles are which type of vesicle? What coat proteins? What GTPase? |
COPI Coatomer ARF GTPase |
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What proteins are associated with clathrin-coated vesicles? What GTPase? |
AP1, AP2, AP3, or GGA ARF GTPase |
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Where do clathrin-coated vesicles go? |
- trans-Golgi to endosomes or lysosomes - PM to endosomes |
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What is the general sequence of COPII vesicle formation? (4) |
1. COPII coat protein binds cytosolic domains of integral membrane cargo or R for soluble cargo 2. Curved COPII causes formation of vesicle, which pinches off ER 3. Vesicle de-coats, exposing v-SNAREs 4. v-SNAREs find t-SNAREs on cic-Golgi, vesicle fusion |
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What ensures that ER resident proteins are retrograde transported back to the ER? |
KDEL sequence (Lys-Asp-Glu-Leu) |
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What determines the loading and unloading of KDEL-proteins? |
pH! pH in cis-Golgi is 6.6, but is 7.1 in ER KDEL-proteins bind receptors at the lower pH, higher pH promotes release of KDEL proteins |
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What is the purpose of the GTPase in vesicle formation? |
GTPase bound GTP: aids in binding of coat protein to target membrane GTPase bound GDP: causes coat to disassemble to expose v-SNAREs |
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What further processing of N-glycosylation occurs in the cis-Golgi? |
removal of three mannose sugars i.e. High Mannose Glycosylation |
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At what place in the Golgi does High Mannose glycosylation occur? How about Complex Glycosylation? |
Mannose: after cis Complex: after trans |
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How does the AP assist in getting the proper cargo to the appropriate type of transport? |
It binds the sorting signal on cargo and interacts with the coat protein (usually clathrin) |
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Transport to lysosome from TGN involves: - which AP? - which GTPase? - which cargo signal? |
AP3 ARF |
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Transport to endosome from TGN involves: - which AP? - which GTPase? - which cargo signal? |
AP1 ARF Tyr-X-X-bulky hydrophobic |
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Transport from plasma membrane to endosome involves: - which AP? - which GTPase? |
AP2 ARF |
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In regulated secretion of vesicles, cargo forms internal aggregates involving.... (3) |
Chromogranin A, Chromogranin B, Secretogranin II |
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Clathrin protein is composed of? |
3 heavy & 3 light chains |
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What is the 2-step process that occurs within the cis-golgi to create the mannose 6-phosphate signal? |
1. UDP-GlcNAc is used to add GluNAc-phosphate to one of the mannose sugars (enzyme: GlcNAc-1-phosphotransferase) 2. GluNAc is then removed (enzyme: phosphodiesterase) |
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What enzyme is defective in Inclusion Cell (I-Cell) disease? What is the result of this? |
GlcNAc phosphotransferase is defective No M6P labeling of lysosomal enzymes |
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What is the less-severe form of I-Cell disease? |
pseudo-Hurler polydystrophy |
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What is the classification of I-Cell Disease? pseudo-Hurler? |
I-Cell: Mucolipidosis II pseudo-Hurler: ML III |
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What are the symptoms of I-Cell disease? |
Coarse features Child reaches milestones, but then regresses Psychomotor retardation, below average growth rate |
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What is the pH of a lysosome? |
5-6 |
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Cytosolic proteins containing what sequence can be selectively taken up by lysosomes? |
KFERQ |
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What GTPase is involved in the budding of a clathrin coated endocytotic vesicle? |
Dynamin |
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What protein promotes de-coating of the clathrin coat on an endocytotic vesicle? |
ARF |
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What are the different domains of the LDL receptor? |
1. Extracellular, ligand-binding domain 2. Extracellular, beta-propeller domain 3. Cytosolic surface, NPYX sorting seq |
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What causes release of the LDL particle within the lysosome? |
- Beta-propeller domain becomes positively charged in the acidic environment, and binds tightly to the ligand-binding domain - this interferes with interactions with ApoB, so the LDL is released |
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What is the molecular basis for familial hypercholesterolemia? |
Mutation in LDL receptor |
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Ferrotransferrin has high affinity for _______ at ______ pH |
High affinity for transferrin R at neutral pH (extracellular matrix) |
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What promotes release of iron from ferrotransferrin? |
High acidity |
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Apotransferrin has high affinity for the transferrin receptor at ______ pH and low affinity for the receptor at ______ pH |
high affinity at low pH low affinity at neutral pH |
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What proteins and protein modifications are critical to invagination of membrane for degradation in the lysosome? |
1. Hrs proteins (monoubiquitinated) 2. ESCRT complex |
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Which HIV protein is analogous to Hrs and allows the HIV to assemble ESCRT and bud? |
HIV Gag protein |