Lecture 6 and 7 Flashcards
What are some ways nuclear transport is regulated?
1) Change the number of nuclear pores
2) Mask the NLS (nuclear localization signal) of cargo proteins
3) Phorphosrylate proteins adjacent to the NLS sequence (inhibits or promotes nuclear transport)
What is an example of how cargo proteins would mask the NLS?
NF-kB (p50/p65) transcription factor complexed with IkB
When is the nuclear envelope broken?
Prior to mitosis
What is the disassembly/reassembly of lamina due to?
Post-translational modifications
How is the nuclear membrane broken down and reassembled (steps)?
1) cdk1:cyclin B phosphorylates two serine residues of all lamins which leads to the breakdown of lamin matrix as mitosis begins
2) Demethylation occurs on lamin B. Remethylation is necessary at the end of mitosis for lamin reassembly. *lamin A and C are not methylated
3) Ran-GEFs remain bound to chromatin during mitosis
When Ran-GEFs remain bound to chromatin during mitosis, what exists around chromatin?
“Cloud” of Ran
What state is Ran in while the “cloud” exists around chromatin?
GTP
How do proteins from the cytosol get to the mitochondria and/or plastids?
Transmembrane transport
What is the key protein transport problem in a cell?
How do the proteins made in the cytoplasm get into and across lipid membranes?
What does the human mitochondrial genome encode?
13 polypeptides (for oxidative phosphorylation), 22 tRNAs, and 2 rRNAs
What are the vast majority of proteins in the mitochondria encoded by? Why?
Nuclear genes (about 1000) because they’re more regulated
What do mitochondrial signal peptides do?
Form amphipathic alpha-helices which interact with membrane receptors
What are protein translocators?
Multisubunit complexes that act as receptors for transport into the mitochondria
What do protein translocators do in the mitochondria?
- Transport nuclear-encoded proteins containing signal peptides into intermembrane space
- Inserts proteins into membrane or transfers proteins to additional translocators
What does the TOM complex do?
Transports outer membrane
What does the TIM complex do?
Transports inner membrane
What is the SAM complex? What does it do?
Sorting Assembly Machinery
- Assists in proper folding
How is a protein transported into the mitochondria (steps)?
1) Free system is used to identify components of transport mechanisms
2) Proteins translated in cytoplasm (unfolded) attach to chaperons
3) Proteins are transported and bind to TOM complex
4) Chaperons are removed and signal peptide is fed through the receptor into the translocation channel (leading to intermembrane space)
5) A signal peptidase in the matrix cleaves off the signal peptide sequence
What is an example of a chaperone?
HSP70 (heat shock protein)
What can hydrophobic sequences do?
Act as “stop” transfer sequences for proteins found in the inner mitochondrial membrane or intermembrane space
What do some inner membrane proteins contain?
Localization signals that direct them to bind to transporters/chaperones
Where is the OXA transporter located?
The inner membrane
What can the OXA transporter do?
- Insert proteins into the membrane based on the internal signal sequence
- Insert mitochondrial-produced proteins into the inner membrane
How do proteins from the cytoplasm end up in peroxisomes?
By direct delivery
