Post-Translational-Import

Question 1

Post translational import

Answer 1

Enter organelles after they’ve been synthesized

Question 2

If synthesized on free ribosomes

Answer 2

Peroxisome/mitochondrion/chloroplast/nuclear interior
Will import directly to the organelles

Question 3

If synthesized on rough ER ribosomes

Answer 3

They need:
1- sorting signal: amino acid sequence
2- receptor: should recognize the sorting signal
3- membrane transporter: facilitate passage into organelle

Question 4

Peroxisomes

Answer 4

-Bounded by single membrane -Defining characteristic of peroxisome is presence of catalase
-Generated by division existing peroxisome or vesicle fusion

Question 5

Peroxisomes role

Answer 5

1- H2O2 metabolism
2- Detoxification
3- Oxidation fatty acids
4- Metabolism of nitrogen-containing compounds
5- Catabolism of unusual substances

Question 6

H2O2 metabolism

Answer 6

—Catalases: enzyme degrade H2O2 into water and oxygen
—Oxidases: enzyme oxidize organic substances and produce H2O2

Question 7

Peroxisomes membrane lipid

Answer 7

Synthesized by peroxisomal enzyme
Or
Transported by lipid transfer protein

Question 8

Peroxisomal proteins

Answer 8

Synthesized on free ribosome
The imported by C-terminal peroxisomal targeting signal

Question 9

Most mitochondrial and chloroplast polypeptides are synthesized on——

Answer 9

Cytoplasmic ribosomes

Question 10

Mitochondrial protein

Answer 10

99% are encoded by nuclear genes
1% mitochondrial genome
Most of them can be found in mitochondrial matrix or inner-mitochondrial membrane

Question 11

Proteins that enter mitochondria must be

Answer 11

In unfolded state
Contain presequence or internal targeting sequence

Question 12

Translocation across both membranes of mitochondria happens

Answer 12

Simultaneously
When the inner and outer membrane are close together

Uses mitochondrial transport complex
TOM AND TIM

Question 13

Targeting mitochondrial matrix proteins

Answer 13

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

Question 14

How mitochondrial proteins are pulled into the matrix

Answer 14

1- chaperons using ATP pull on peptide
2- random diffusion allow peptide to bind with chaperone diffuse further then another chaperone
BROWNIAN RATCHET

Question 15

Targeting of inner mitochondrial membrane

Answer 15

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

Question 16

Chloplast

Answer 16

Inner and outer membrane
Flattened membranous sacs thylakoids third layer

Question 17

Chloroplast protein transport

Answer 17

-stroma targeting domain which is removed by peptidase upon transport
-thylakoid transfer membrane is needed for entry to thylakoid

Question 18

Nucleus

Answer 18

Enzyme and proteins must imported in
AND
mRNA and ribosome must exported out of the cell

Question 19

Nuclear envelope layers

Answer 19

Inner membrane (define nucleus)
Outer membrane (same with ER)

Nuclear pores: fuse the two membrane, transport between cytoplasm and nucleoplasm

Question 20

Cytosol to nuclear materials

Answer 20

Histones
Dna/Rna polymerase
Ribosomal protein
Transcription factor

Question 21

Nucleus to cytosol

Answer 21

tRna
mRna
rNP complexes

Question 22

Nuclear pore complex

Answer 22

30 different proteins called nucleoporins

Question 23

Central granule in nuclear pore complex is

Answer 23

Transporter
Moving molecules across the nuclear envelope

Question 24

NPC transport

Answer 24

Small molecules can diffuse by aqueous diffusion channels
Large molecules = active transport

Question 25

Large molecules should have ——— or ——— to be able to identify by NpC

Answer 25

Nuclear Localization Signal (8-30 AA contains proline and arginine and lysine
Nuclear Export Signal

Question 26

Import protein through nuclear pores

Answer 26

Increase cell order
And
Require energy

Question 27

Energy for NPC

Answer 27

Provided by hydrolysis of GTP by GTPase Ran

Ran-GDP ——Ran-GEF—> Ran-GTP

Question 28

Import/importin

Answer 28

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

Question 29

Ran-GTP inside vs outside

Answer 29

Inside high
Outside low

Question 30

Ran-GDP inside vs outside

Answer 30

Inside low
Outside high

Question 31

Importin inside vs outside

Answer 31

Inside low
Outside high

Question 32

Export/exportin

Answer 32

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