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3108 > targeting to peroxisomes and nucelus > Flashcards

targeting to peroxisomes and nucelus Flashcards

1
Q

what are peroxisomes

A

very small spherical organelles that contain more than 50 diff enzymes

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2
Q

what do peroxisomes do

A

oxidise organic compounds and break down fatty acids and degrade hydrogen peroxides

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3
Q

how do peroxisomes degrade hydrogen peroxides

A

generate H202 as byproduct of redox reactions then use catalase to convert it to water and oxygen

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4
Q

what are peroxisomal luminal proteins encoded by

A

nuclear genes

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5
Q

where are peroxisomal luminal proteins synth

A

on free ribosomes in the cytosol and incorporated into preexisting or newly generated peroxisomes

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6
Q

what is the c terminal peroxisomal targeting sequence recognized by

A

PTS1
recognized by cytosolic receptor that targets proteins for transport to peroxisome lumen

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7
Q

steps of targeting peroxisomal luminal proteins

A
  1. PTS1 binds to cytosolic receptor Pex5
  2. forms multimeric complex with pex14 receptor- size of complex adjusts to size of protein
  3. protein dissociates but targetting sequence is retained
  4. pex5 ubiquitinated by pex membrane proteins
  5. pex5 is removed from the membrane- ATP dependant
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8
Q

what does PTS1 bind to and what does that complex bind with

A

pex 5 and the complex binds with the pex 14 receptor

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9
Q

nucelar membrane

A

double membrane- envelope separated by perinuclear space

outer membrane is continous with rough endoplasmic reticulum

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10
Q

what is the nuclear membrane devoid of

A

protein and sugars

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11
Q

how are things tranpsorted into and out of the nucleus

A

via large nuclear pore complexes unidirectionally

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12
Q

what size of proteins go though nuclear pore compexes

A

no larger than 40kDa

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13
Q

what does nuclear pore tranport require

A

nuclear localization or nuclear export signal and various proteins- nuclear transport receptors, Ran G-proteins, and localized Ran-GEFs and GAPs

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14
Q

what is transported by a Ran-independant pathway

A

other molecules invluding mRNPs

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15
Q

where are nucelar pores found

A

span both membranes- connect inside to outside

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16
Q

what do nuclear pores consist of

A

more than 100 proteins making them one of fhte largest protein complexes in eukaryotes
have an octagonal shape channel with radial symmetry

17
Q

FG

A

phenyalanine- F
glycine- G

18
Q

what do nucleopris do

A

line the central channel of the pore

19
Q

what is the makeup of nucleoporins

A

long random coil stretches extending into the channel setting up a semipermeable barrier

20
Q

nuclear pore- transport of proteins smaller than 10

A

passively controlled by concentration

21
Q

nuclear pore- transport of proteins 10-40

A

passive but regulated by calcium

22
Q

nuclear pore- transport of proteins larger than 40

A

active transport that requires a signal interacting with a receptor- importin

the source of energy is GTP

23
Q

where is importin

A

cytoplasm

24
Q

what does importin bind to

A

NSL forming an importing- cargo complex

25
Q

what does the importin cargo complex do

A

diffuses through NPC via transient interaction with FG nucleoporins

26
Q

what happnes to Ran-GDP

A

diffuses into nucleus and is activated by GEF to become Ran-GTP

27
Q

what happens to Ran-GTP

A

binds to importin resulting in a conformational change that releases cargo

28
Q

what happens to the importin-Ran-GTP complex

A

it is transported to the cytoplasm where a GTPase activating protein GAP stimulates GTP hydrolysis leading a confromational change releasing importin

29
Q

what does the localization of GEF in the ncelus and GAP in the cytoplasm do

A

creates a gradient of high ran-GTP concentration in the nucleoplasm and high RAN-GDP in th ecytoplasm ensuring proper direction of nuclear import

30
Q

where is GEF localized

A

in the nucleus

31
Q

where is GAP localized

A

in the cytoplasm

32
Q

what do small GTPases include

A

a large family of proteins such as RAS proteins (Ran- RAs related Nuclear protein)

33
Q

what do small GTPases do

A

act as a molecular switch- bind and hydrolyze GTP to GDP at a low rate

34
Q

GAP

A

GTPase activating proteins
increase rate of hydrolysis

35
Q

GEF

A

GTP exchange factors
remove GDP (allow GTP to bind)

36
Q

what does exporting 1 do

A

forms a compex with NES-cargo protein and Ran-GTP in the nucleoplasm
this complex diffuses through the NPC

37
Q

what does Ran-GAP do

A

RanGAP associated with cytoplasmic fillaments stimulates Ran-GTP hydrolysis resulting in a confromational chagne that releases cargo in the cytossol

38
Q

what is the end fate of exportin 1 and Ran-GDP

A

tranpsorted back to nucleus

39
Q

what does Ran-GEF in the cytoplasm do

A

converts Ran-GDP to Ran-GTP

3108 (9 decks)

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