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BSCI330 SPRING > exam 3 intracellular protein transport > Flashcards

exam 3 intracellular protein transport Flashcards

1
Q

where does translation begin

A

cytosol

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2
Q

where are proteins synthesized

A

cytosol, then transported to membrane-enclosed organelles

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3
Q

what does transport rely on

A

specific signal sequences within the protein primary sequence

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4
Q

what does gated transport do

A

moves proteins into and out of the nucleus from cytosol through nuclear pore complexes

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5
Q

how are proteins transported into the mitochondira

A

via transmembrane transport through the TOM and TIM complexes

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6
Q

how are proteins imported into the ER

A

via co-translational transport

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7
Q

what are eukaryotic cells subdivided into

A

functionally distinct, membrane-enclosed compartments

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8
Q

what is the cytoplasm

A

cytosol + organelles

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9
Q

what occurs/is in the cytosol

A

where protein synthesis and degradation occurs

where proteasome is

where metabolism occurs

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10
Q

where does transmembrane transport go to

A

mitochondria, ER, plastids, peroxisomes

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11
Q

what is the movement of proteins between organelles consistent with

A

topological similarities among the compartments

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12
Q

what are topological similarities and what do they allow for

A

compartments with similar membrane orientations - allows for same transport

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13
Q

what is the movement of proteins between organelles mediated by

A

sorting signals and receptors

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14
Q

what are the three fundamental mechanisms of transport of proteins

A

gated, transmembrane, and vesicular transport

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15
Q

what do nuclear pore complexes function as

A

selective gates that actively transport specific macromolecules and assemblies, which allows for free diffusion of smaller molecules

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16
Q

what is transmembrane transport

A

protein traffic between the cytosol and an organelle that is topologically different (i.e. cytosol to ER)

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17
Q

what does transmembrane transport occur through

A

membrane-bound protein translocators

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18
Q

what is vesicular transport

A

protein traffic among topologically equivalent organelles

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19
Q

where does vesicular transport occur through

A

membrane-enclosed transport intermediates called vesicles

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20
Q

what organelles do vesicular transport occur between

A

ER and golgi

golgi and lysosomes

endosomes and plasma membrane

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21
Q

what restricts the passage of large macromolecules in gated transport

A

nuclearporins lining the central pore containing unstructured regions

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22
Q

how do nuclearporins act as gates

A

they don’t have a strong tertiary structure, which allows them to move from one conformation to another - energy dependent

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23
Q

what does moving up a concentration gradient require

A

active transport

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24
Q

how is nuclear import initiated in gated transport

A

nuclear localization signals within the cargo are recognized by nuclear import receptors

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25
Q

where are nuclear localization signals present

A

nuclear proteins

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26
Q

what is the signal for nuclear import made up of

A

five basic amino acids in a row

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27
Q

what does nuclear transport do

A

concentrates specific proteins in the nucleus, increasing order in the cell and consuming energy

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28
Q

what is the energy in nuclear transport provided by

A

hydrolysis of GTP by Ran

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29
Q

what is Ran

A

a small GTPase

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30
Q

what does GEF do for nuclear transport

A

activates protein

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31
Q

what does GAF do for nuclear transport

A

speeds up hydrolysis of GTP to GDP to deactivate protein

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32
Q

where is Ran found

A

in both the cytosol and nucleus

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33
Q

what is Ran required for

A

both the nuclear import and export systems

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34
Q

what is import deactivated by (gated transport)

A

RAN-GTP (releases cargo)

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35
Q

what is export activated by (gated transport)

A

RAN-GTP (picks up cargo)

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36
Q

what does control of nuclear transport depend on

A

regulation of nuclear localization and export signals

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37
Q

what are the two states Ran exists in

A

one with GTP attached and one with GDP attached

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38
Q

what is RAN-GEF

A

nuclear protein - catalyses the binding of GTP to RAN inside the nucleus

39
Q

what is RAN-GAP

A

a cytosolic protein - activates hydrolysis of GTP attached to RAN

40
Q

what creates a RAN-GTP gradient

A

hydrolysis of GTP attached to RAN because there is more RAN GTP inside the nucleus than outside

41
Q

what occurs after RAN-GTP binds to the nuclear import receptors

A

happens after they diffuse through nuclear pore and into nucleus - causes them to release their cargo proteins which accumulate inside nucleus

42
Q

what is the effect of RAN-GTP on nuclear export receptors

A

they bind to their cargo

43
Q

which RAN associates or dissociates

A

RAN-GDP dissociates from receptors, RAN-GTP binds to receptors

44
Q

what does binding to RAN cause

A

release of the cargo and allows the receptor to bind back to nuclear pore and be shuttled outside the nucleus into cytoplasm

45
Q

where is RAN-GDP in

A

cytoplasm

46
Q

where is RAN-GTP in

A

nucleus - forces release of cargo

47
Q

what does hydrolysis of GTP to GDP cause

A

dissociation of RAN from import and export receptors

48
Q

how is activity of gene regulatory proteins controlled

A

by keeping them out of the nuclear compartment until they are needed there

49
Q

how are T cells activated

A

by antigen binding

50
Q

why do calcium levels increase

A

calcium channel opening - activates the protein phosphatase, calcineurin

51
Q

what does calcineurin dephosphorylate and what does it cause

A

NFAT - causes a conformational change which exposes a nuclear import sequence on the protein’s surface

52
Q

what happens with mitochondrial transport

A

mitochondrial proteins are first fully synthesized as precursor proteins in the cytosol and then translocated into mitochondria

53
Q

what do most mitochondrial precursor proteins have

A

a signal sequence at their N terminus that, when folded, forms an amphipathic alpha helix

54
Q

what residues does a signal sequence at the N terminus have

A

charged residues clustered on one side, uncharged residues clustered on the other side

55
Q

what does the TOM complex does

A

transports across the outer membrane

56
Q

what does the TIM complex do

A

transports across the inner membrane (imbedded in inner mitochondrial membrane)

57
Q

why is TOM considered a gatekeeper

A

all proteins that are going to get in the mitochondria have to interact with it

58
Q

what does TOM help with

A

helps insert transmembrane proteins into outer mitochondrial membrane

59
Q

what does TIM get proteins into

A

intermembrane space of mitochondria, including matrix

60
Q

what does TIM 23 span

A

both outer and inner mitochondrial membranes

61
Q

what does TIM transport

A

soluble proteins into matrix and membrane proteins into inner mitochondrial membrane

62
Q

what are newly synthesized mitochondrial proteins in the cytosol surrounded by

A

protein-folding chaperones that prevent them from aggregating

63
Q

what do mitochondrial versions of chaperones do

A

help precursor proteins fold into 3D structures once they enter the mitochondria

64
Q

why does directional transport require energy

A

it is not energetically favorable

65
Q

what does mitochondrial protein import require

A

ATP

66
Q

what is cytosolic chaperone disassembly driven by

A

ATP hydrolysis

67
Q

where are proteins synthesized for both gated and transmembrane transport

A

cytosol

68
Q

where does gated transport move through

A

nuclear pores using nuclear import and export receptors and RAN GDP and GTP cycle****know these for exam

69
Q

where is the precursor synthesized for mitochondrial transport

A

the cytosol and kept in slightly unfolded state to be shuttled through TOM and TIM transporters into mitochondria

70
Q

what is nuclear import done through

A

GTP hydrolysis

71
Q

what is mitochondrial import done through

A

ATP hydrolysis

72
Q

what is the protein gradient a source of energy for

A

transporting across mitochondria membrane

73
Q

what type of transport are gated and transmembrane transport

A

active

74
Q

what do proteins entering the ER undergo

A

Co-translational translocation

75
Q

how is transport into ER different than transport into nucleus and mitochondria

A

proteins are not fully synthesized before they are transported into ER

76
Q

what is happening to proteins simultaneously as they’re going into the ER

A

they’re being transported as they’re being translated

77
Q

how do proteins enter the ER

A

as ribosome is translating the protein, near N-terminus a signal sequence marks this protein as one to be transported into ER

signal pauses translation and directs whole complex to move to ER; when translation restarts, the protein is pushed across the membrane as it’s being translated

78
Q

what types of proteins require co-translational translocation

A

water soluble (non membranous) proteins destined to:

  • localize to the lumen of any non-nuclear organelle (ER, golgi, lysosomes, etc)
  • be secreted out of the cell (e.g. hormones)
79
Q

what are SRPs

A

proteins that contain both RNA and polypeptide components

80
Q

what are the 2 functional domains of SRPs

A
  • translational pause domain, which interacts with ribosome and prevents binding of elongation factors (EF2, etc - which bring in new tRNAs), therefore pausing translation
  • signal-sequence-recognizing component
81
Q

what does signal sequence recognizing component do

A

stops translation and can be recognized by SRP receptor on ER

82
Q

what happens if the signal sequence is near the N-terminus as translation happens

A

very hydrophobic region of the protein that is now accessible and recognized by SRP

83
Q

what happens when SRP binds to the signal sequence

A
  • it positions translational pause domain to interact with the elongation factor binding site
  • the ribosome pauses in translation and the whole complex can be brought to ER where it interacts with SRP receptor
  • this now gives appearance of rough ER
84
Q

what happens once SRP binds to its receptor

A

it transfers the polypeptide to a protein translocator machinery (i.e. TOM), allowing protein to be threaded across ER membrane as its being translated

85
Q

why is there no protein requirement for SRP

A

the process occurs before protein is folded

86
Q

what generates a force to push a polypeptide out of a ribosome

A

adding a new amino acid to the polypeptide

87
Q

what is the transmembrane region a stretch of

A

highly hydrophobic stretch of at least 8 amino acids

88
Q

what happens to the transmembrane region as we’re synthesizing proteins

A

any time there is this long stretch, it gets stuck in membrane as transmembrane region
- some portions are pushed into ER, synthesized into cytosol, stuck in membrane as we push it back and forth across the membrane as many times is needed to have enough transmembrane regions

89
Q

what happens if there is a single transmembrane region

A

we have signal sequence (start transfer sequence); thread polypeptide through until we reach another polypeptide stretch (stop transfer sequence - gets recognized and stuck in membrane); next hydrophobic would start transfer, and so on

90
Q

what cleaves off signal peptide

A

signal peptidase enzyme - now N-terminus is in ER lumen; C-terminus is in cytosol; threading continues until C-terminus is in ER lumen

91
Q

how do cells know where N-terminus and C-terminus should be in transmembrane regions

A

on either side of hydrophobic regions, first region that serves as start transfer has positive amino acid on one end and negatively charged amino acid at another.
- the side with the positively charged amino acid is going to face the cytosol (positive charge is n-terminus); negative charge faces lumen of ER

92
Q

how do cells know where N-terminus and C-terminus should be in transmembrane regions if we have multi-pass polypeptide

A

hydrophobic regions = # transmembrane regions

  • odd # regions = n terminus and c terminus are on opposite sides of ER membrane
  • even # = will be on same side of membrane
93
Q

what happens if positive charge is on n-terminal side

A

n-terminal will face cytosol

94
Q

what happens if negative charge is towards n-terminal side

A

n-terminal faces lumen

BSCI330 SPRING (24 decks)

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