targeting to peroxisomes and nucelus

Question 1

what are peroxisomes

Answer 1

very small spherical organelles that contain more than 50 diff enzymes

Question 2

what do peroxisomes do

Answer 2

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

Question 3

how do peroxisomes degrade hydrogen peroxides

Answer 3

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

Question 4

what are peroxisomal luminal proteins encoded by

Answer 4

nuclear genes

Question 5

where are peroxisomal luminal proteins synth

Answer 5

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

Question 6

what is the c terminal peroxisomal targeting sequence recognized by

Answer 6

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

Question 7

steps of targeting peroxisomal luminal proteins

Answer 7

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

Question 8

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

Answer 8

pex 5 and the complex binds with the pex 14 receptor

Question 9

nucelar membrane

Answer 9

double membrane- envelope separated by perinuclear space

outer membrane is continous with rough endoplasmic reticulum

Question 10

what is the nuclear membrane devoid of

Answer 10

protein and sugars

Question 11

how are things tranpsorted into and out of the nucleus

Answer 11

via large nuclear pore complexes unidirectionally

Question 12

what size of proteins go though nuclear pore compexes

Answer 12

no larger than 40kDa

Question 13

what does nuclear pore tranport require

Answer 13

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

Question 14

what is transported by a Ran-independant pathway

Answer 14

other molecules invluding mRNPs

Question 15

where are nucelar pores found

Answer 15

span both membranes- connect inside to outside

Question 16

what do nuclear pores consist of

Answer 16

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

Question 17

FG

Answer 17

phenyalanine- F
glycine- G

Question 18

what do nucleopris do

Answer 18

line the central channel of the pore

Question 19

what is the makeup of nucleoporins

Answer 19

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

Question 20

nuclear pore- transport of proteins smaller than 10

Answer 20

passively controlled by concentration

Question 21

nuclear pore- transport of proteins 10-40

Answer 21

passive but regulated by calcium

Question 22

nuclear pore- transport of proteins larger than 40

Answer 22

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

the source of energy is GTP

Question 23

where is importin

Answer 23

cytoplasm

Question 24

what does importin bind to

Answer 24

NSL forming an importing- cargo complex

Question 25

what does the importin cargo complex do

Answer 25

diffuses through NPC via transient interaction with FG nucleoporins

Question 26

what happnes to Ran-GDP

Answer 26

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

Question 27

what happens to Ran-GTP

Answer 27

binds to importin resulting in a conformational change that releases cargo

Question 28

what happens to the importin-Ran-GTP complex

Answer 28

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

Question 29

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

Answer 29

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

Question 30

where is GEF localized

Answer 30

in the nucleus

Question 31

where is GAP localized

Answer 31

in the cytoplasm

Question 32

what do small GTPases include

Answer 32

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

Question 33

what do small GTPases do

Answer 33

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

Question 34

GAP

Answer 34

GTPase activating proteins increase rate of hydrolysis

Question 35

GEF

Answer 35

GTP exchange factors remove GDP (allow GTP to bind)

Question 36

what does exporting 1 do

Answer 36

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

Question 37

what does Ran-GAP do

Answer 37

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

Question 38

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

Answer 38

tranpsorted back to nucleus

Question 39

what does Ran-GEF in the cytoplasm do

Answer 39

converts Ran-GDP to Ran-GTP