MCB Lecture 31 Gated Transport & Transmembrane Transport Flashcards
Describe the structure of a nuclear pore
Octamer: eight proteins line the pore complex
How do molecules get in and out of the nucleus?
Gated transport
How do larger molecules get across the nuclear envelope?
Need a translocator
- Nuclear Localisation Sequence found in protein
- Nuclear Import Receptor recognises the NLS
- Protein is shuttled through the Nuclear Pore Complex on the Nuclear Import Receptor
- Ran-GTPase hydrolysis GTP, cargo dissociates in the nucleus
- GDP dissociates on the cytosol side
What is the name of the sequence that is recognised on a protein for its import into the nucleus?
Nuclear localisation sequence
What is the name of the receptor that moves proteins into the nucleus?
Nuclear import receptor
What are the features of the nuclear localisation sequence?
Lysine rich
15-60 amino acids long
Describe the steps involved with exporting a protein from the nucleus
Same as the import, except the protein binds to the Nuclear Import Receptor on the inside, as well as Ran-GTP.
Ran-GTP is hydrolysed in the cytosol, and the cargo is released
Describe the function of Ran-GTPase
Hydrolysis GTP in the cytosol
Where are nuclear proteins synthesised?
In the cytosol
When do nuclear proteins fold?
In the cytosol
How is the import of nuclear proteins regulated?
Phosphorylation of a protein causes conformational change, and the Nuclear Localisation Sequence is exposed
Now, the protein can be imported
When is transmembrane transport used?
To move protein from the cytosol into the mitochondria or ER
Describe how proteins traverse the two mitochondrial membranes
- Signal sequence on protein recognised by the TOM receptor
- TOM and TIM line up in the membranes -> translocation channel
- The protein is fed through into the matrix of the mitochondria
- Signal sequence cleaved
- Protein folds
Describe the features of the signal sequence for proteins entering the mitochondria
The signal sequence is an amphiphilic sequence.
The receptor I recognises the hydrophobic region
Describe the structure of the translocation channels on the mitochondrial membrane
TOM on outer membrane
TIM on inner membrane