Post-Translational-Import Flashcards
Post translational import
Enter organelles after they’ve been synthesized
If synthesized on free ribosomes
Peroxisome/mitochondrion/chloroplast/nuclear interior
Will import directly to the organelles
If synthesized on rough ER ribosomes
They need:
1- sorting signal: amino acid sequence
2- receptor: should recognize the sorting signal
3- membrane transporter: facilitate passage into organelle
Peroxisomes
-Bounded by single membrane -Defining characteristic of peroxisome is presence of catalase
-Generated by division existing peroxisome or vesicle fusion
Peroxisomes role
1- H2O2 metabolism
2- Detoxification
3- Oxidation fatty acids
4- Metabolism of nitrogen-containing compounds
5- Catabolism of unusual substances
H2O2 metabolism
—Catalases: enzyme degrade H2O2 into water and oxygen
—Oxidases: enzyme oxidize organic substances and produce H2O2
Peroxisomes membrane lipid
Synthesized by peroxisomal enzyme
Or
Transported by lipid transfer protein
Peroxisomal proteins
Synthesized on free ribosome
The imported by C-terminal peroxisomal targeting signal
Most mitochondrial and chloroplast polypeptides are synthesized on——
Cytoplasmic ribosomes
Mitochondrial protein
99% are encoded by nuclear genes
1% mitochondrial genome
Most of them can be found in mitochondrial matrix or inner-mitochondrial membrane
Proteins that enter mitochondria must be
In unfolded state
Contain presequence or internal targeting sequence
Translocation across both membranes of mitochondria happens
Simultaneously
When the inner and outer membrane are close together
Uses mitochondrial transport complex
TOM AND TIM
Targeting mitochondrial matrix proteins
1- cytosolic proteins are bound by molecular chaperones to keep them unfolded
2- presequence bind receptor TOM on outer mitochondrial membrane and goes into TOM channel
3- TOM and TIM channels are brought together
4- movement is powered by electrical potential
5- mitochondrial process are pulled into matrix
6- once in matrix, presequence is cleaved by peptidase
7- protein folded to native conformation
How mitochondrial proteins are pulled into the matrix
1- chaperons using ATP pull on peptide
2- random diffusion allow peptide to bind with chaperone diffuse further then another chaperone
BROWNIAN RATCHET
Targeting of inner mitochondrial membrane
1- cytosolic proteins bind with chaperons to keep them unfolded
2- presequnce bind to receptor component TOM on outer membrane mitochondria and positioned into TOM channel
3-TOM and TIM brought together
4- Internal targeting sequence signal TIM to allow protein passing the bilayer
Chloplast
Inner and outer membrane
Flattened membranous sacs thylakoids third layer
Chloroplast protein transport
-stroma targeting domain which is removed by peptidase upon transport
-thylakoid transfer membrane is needed for entry to thylakoid
Nucleus
Enzyme and proteins must imported in
AND
mRNA and ribosome must exported out of the cell
Nuclear envelope layers
Inner membrane (define nucleus)
Outer membrane (same with ER)
Nuclear pores: fuse the two membrane, transport between cytoplasm and nucleoplasm
Cytosol to nuclear materials
Histones
Dna/Rna polymerase
Ribosomal protein
Transcription factor
Nucleus to cytosol
tRna
mRna
rNP complexes
Nuclear pore complex
30 different proteins called nucleoporins
Central granule in nuclear pore complex is
Transporter
Moving molecules across the nuclear envelope
NPC transport
Small molecules can diffuse by aqueous diffusion channels
Large molecules = active transport
Large molecules should have ——— or ——— to be able to identify by NpC
Nuclear Localization Signal (8-30 AA contains proline and arginine and lysine
Nuclear Export Signal
Import protein through nuclear pores
Increase cell order
And
Require energy
Energy for NPC
Provided by hydrolysis of GTP by GTPase Ran
Ran-GDP ——Ran-GEF—> Ran-GTP
Import/importin
1- cytoplasmic protein with NLS recognized by importin
2- importin-protein complex will go in from NPC
INSIDE THE CELL:
3- importin associate with Ran-GTP, releasing NLS protein
4- Ran-GTP-importin transported back by NPC
5- in cytoplasm GTP hydrolyzed and importin is released
Ran-GTP inside vs outside
Inside high
Outside low
Ran-GDP inside vs outside
Inside low
Outside high
Importin inside vs outside
Inside low
Outside high
Export/exportin
Ran-dependent export
1-Ran-GTP bind exportin
2- Ran-GTP-Exportin bind NES
3- Export happens
4- GTp is hydrolyzed
5- Exportin is imported back
