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Cell Physiology - Unit 3 > Protein Targeting > Flashcards

Protein Targeting Flashcards

1
Q

process of making type-II single-pass proteins

A
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2
Q

BIP

A

chaperone that keeps protein chain from folding

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3
Q

where do secretory proteins go shortly after synthesis?

A

secretory proteins are localized in the ER lumen shortly after synthesis

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4
Q

name of guy responsible for understanding secretory pathway

A

Blobel

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5
Q

what if a protein is going to mitochondria somewhere other than the matrix?

A

most mitochondrial proteins go to the matrix, but if a protein is going elsewhere then it will first go to the matrix and then to its destination from the matrix

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6
Q

location of N-term and C-term in single-pass transmembrane protein

A

N-term: ER lumen

C-term: cytosol/cytoplasm

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7
Q

hydrophobic regions in secretory and single pass proteins

A
  • signal peptide
  • stop-transfer sequence
  • signal-anchor sequence
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8
Q

NLS

A

nuclear localization signal; signal that is put on in the middle of a protein to indicate that the protein belongs in the nucleus

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9
Q

specificity of importin

A

importin is not cargo specific

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10
Q

process of making single-pass transmembrane protein

A

page 3 notes

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11
Q

how are sugar moieties added onto proteins in the golgi?

A

there are different enzymes for different sugars, and there are different enzymes in each cisterna so sugars getted added in in different cisternae of the golgi complex

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12
Q

protein synthesis in nucleus

A

all proteins that are found in the nucleus are synthesized in the cytoplasm and transported to the nucleus via nuclear pore complexes

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13
Q

experiment: requirement of cytosolic proteins for nuclear transport

A
  • treatment with digitonin (detergent) makes the plasma membrane permeable such that the cytosolic constituents leak out but leave the nuclear envelope and pore intact
  • accumulation of transport substrate in nucleus occurred only when cytosol was included in the incubation
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14
Q

trans-face of golgi also called:

A

leaving face

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15
Q

In cotranslational translocation, what is the source of energy that drives protein into the ER lumen?

A

the energy comes from the translation process – translation drives the process

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16
Q

Hydrophobicity Plot

A

evaluates moving averages of hydrophobicity of sections

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17
Q

process: endocytic pathway for internalizing LDL

A
  • cell-surfcae LDL receptors bind to apoB protein which is embedded into the phospholipid outer layer of LDL
  • cell-surface receptors located in Clathrin-coated pit
  • clathrin-coated pits with receptor LDL complex pinch off of plasma membrane to become coated vesicle
  • vesicle coat sheds off; early endosome fuses with late endosome
    • pH difference in late endosome causes receptor to release LDL
  • late endosome fuses with lysosome
  • LDL receptor recycled to cell srface; neutral pH of exterior returns to receptor to active conformational change
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18
Q

function of rough ER

A

synthesis of secreted proteins and post-translational modification

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19
Q

importance of NLS considering the cell cycle

A

in the cell cycle the nuclear envelope breaks down in Prophase and releases nuclear proteins; it is important that these proteins have NLS to indicate that they should go back into the nucleus

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20
Q

process: nuclear import of protein

A
  • importin binds to NLS of a cargo protein in the cytoplasm
  • importin-protein complex diffuses through the nuclear pore complex (NPC) via interaction of F-G repeats
  • in nucleoplasm, Ran-GTP binds importin –> this causes a conformational change so import releases protein
  • import-RanGTP complex diffuses through NPC to cytoplasm
  • Ran-GAP (GTPase activating protein) hydrolyzes bound GTP of Ran-GTP to GDP –> conformational change makes release of importin
  • cycle repeats
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21
Q

SRP functions

A
  • binds to signal peptide
  • arrest translation
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22
Q

viruses and NPCs

A

viruses can take advantage of NPCs to use cell nucleus components (dangerous!)

23
Q

how does a ribosome get recruited to the ER membrane?

A

there is an ER signal sequence on the translated protein

24
Q

how does a vesicle fuse with its target membrane?

A

after being released and shedding its coat, a vesicle fuses with its target membrane using interaction of SNARE proteins

25
Q

import of proteins into mitochondria: cotranslational or post-translational?

A

post-translational

26
Q

experiment that showed post-translational import to mitochondria

A
  • yeast mitochondrial proteins made by cytoplasmic ribosomes in cell-free environment
  • add mitochondria and sample without mitochondria
  • add trypsin – sample without mitochondria led to degraded proteins and sample with mitochondria were protected
27
Q

clathrin

A
  • coat protein that is involved in the making of vesicles
    • collectively multiple clathrin cause the formation of a depression that deforms a membrane allowing formation of a vesicle
  • spherical in shape
28
Q

Fuctions of ER and Golgi

A
  • post-translational modification (such as adding GPI anchor)
  • putting sugar moieties onto proteins
29
Q

difference between membrane-bound and cytosolic ribosomes

A

membrane-bound and cytosolic ribosomes are the same – ribosomes are recruited to the ER during protein synthesis when there’s an ER signal sequence

30
Q

what is cotranslational translocation?

A

normal translation at first but as protein is translated it is guided into the ER lumen

31
Q

SRP acronym

A

signal recognition particle

32
Q

Experiment: in vitro translation of secretory protein in the absence and presence of microsomes

A

no microsomes present

  • no incorporation into microsomes

microsomes present

  • mature protein made its way into microsome and signal sequence was not present

conclusion

  • during translation there is cotranslational transport of protein into the microsome and removal of the signal sequence
33
Q

Process: protein import into the mitochondrial matrix

A
  • proteins synthesized on cytosolic ribosomes; kept unfolded via chaperones (Hsc70)
  • precursor protein binds to import receptor
  • protein transferred to general import pore
  • protein moves through TOM and TIM
  • in matrix, protein binds Hsc70 which helps move protein along
  • uptake-targeting sequence removed by matrix protease and Hsc70 released
  • protein folds into mature, active conformation within matrix
34
Q

cis-face of golgi also called:

A

forming face

35
Q

GPI anchor

A

anchors proteins to extracellular face

36
Q

experiment that found that secretory proteins are in microsomes

A

labeled secretory proteins in rough ER homogenized microsomes with attached ribsomes

added detergent and protease

  • protein degraded

added only protease

  • protein safe – protease couldn’t get to the protein because it was in a microsome
37
Q

nuclear pore transport rate

A

60,000 proteins transferred per minute per pore

38
Q

describe the ER signal sequence

A
  • N-term
  • hydrophobic
  • gets cut off in the microsomal fraction (ER)
39
Q

experiment demonstrating significance of NLS for nuclear protein transport

A

NLS was added to a protein that’s normally found in the cytoplasm; the protein was imported into the nucleus

40
Q

import of peroxisomal matrix proteins

A
  • c-term uptake-targeting sequence binds to cytosolic receptor Pex5
  • Pex5 forms complex with Pex14 receptor which is on the peroxisome membrane
  • Pex5 with protein transferred into peroxisomal matrix then Pex5 dissociates and goes back to cytosol
41
Q

all type-I transmembrane proteins possess:

A
  • N-term signal sequence that targets them to ER
  • internal hydrophobic sequence –> becomes the membrane-spanning alpha-helix
42
Q

how many flattened sacs do golgi typically have?

A

5-6

43
Q

process of cotranslational translocation

A
  • ER signal sequence translated; emerges from ribosome
  • SRP (signal recognition peptide) binds signal sequence
  • SRP delivers ribosome and polypeptide to SRP receptor on ER membrane
    • GTP helps bind/hold these
  • ribsome/polypeptide connect to translocon; translocon opens
  • polypeptide with signal sequence pushed into central pore
  • SRP and SRP receptor dissociate from translocon and hydrolyze their bound GTP to GDO
  • as polypeptide elongates, passes through translocon into the ER lumen; signal sequence cleaved by signal peptidase and degraded
  • when traslation complete: ribosome released, rest of protein drawn into ER lumen, translocon closes, protein assumes native conformation
44
Q

post-translational translocation

A
  • translocating polypeptide chain to translocon; signal sequence cleaved
  • protein chain moves up and down randomly –> BIP binds to chain on down movement (then can’t backtrack)
45
Q

Type IV transmembrane proteins

A

there are multiple transmembrane portions and each has a stop-transfer sequence

46
Q

two notable features of process of peroxisomal matrix protein import

A
  1. signal sequence is left on the protein
  2. signal sequence is on the C-term
47
Q

organelles that protein passes through in secretory pathway

A

ER –> Golgi –> plasma membrane

48
Q

orientation of protein in type-II single-pass proteins

A

C-term is located in the ER lumen (orientation is reversed by type I)

49
Q

signal peptide for keeping protein in the ER

A

KDEL

50
Q

GTP-ase ARF and coat vesicles

A

GTPase ARF involved in the formation of coat proteins (whether assembling or disassembling)

51
Q

sorting signal for protein to be taken to lysosome

A

mannose-6-phosphate

52
Q

how a cell knows to stop dividing

A

integrin can sense the surroundings of a cell; can sense if a dish is confluent

53
Q

receptor that can sense mechanical force

A

integrin receptor

Cell Physiology - Unit 3 (3 decks)

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