Zaidi Lecture 1 9/17 Flashcards
What are the 3 topological categories?
- nucleus and cytosol- communicate through the nuclear pore complex
- organelles in the secretory and endocytic pathways
- mitochondria
How do the organelles in the secretory and endocytic pathways communicate with each other and with the cell exterior?
through budding and fusion
Define gated transport
between the nucleus and the cytosol through the nuclear pore complex
uses active transport and diffusion
Define transmembrane transport
protein trans locators transport proteins from the cytosol across the membrane
Define vesicular transport
uses vesicles between the compartments
What is a sorting signal?
A stretch of 15-60 amino acids at the N or C terminus that help in protein sorting
what is the signal peptidase
can remove the signals after the protein reaches its final destination—trap
How are the signal sequences recognized?
complementary receptors
When importing into the nucleus, which signal is needed?
A lot of lysines and arginine
When importing a cell into the mitochondria, which signal is needed?
combo of positive charges and hydrophobic amino acids
When importing a cell into the ER, what signal sequence is needed?
hydrophobic amino acids
When returning a protein into the ER, what signal sequence is needed?
KDEL (lys, asp, glu, leu)
Describe nuclear transport
gated
bidirectional
selective
Which proteins are imported into the nucleus from the cytosol?
histones, DNA and RNA polymerases, topoisomerase, etc
Which proteins are exported from the nucleus to the cytosol?
tRNA and mRNA molecules
Describe NPCs
- in nuclear envelop
- 30+ proteins (nucleoporins)
- basket like (octagon)
- both directions
- passive diffusion of small molecules and facilitated transport
- transport via binding to fibrils- have a FG repeat that allows for import receptors to bind
What are NLS?
sorting signals that take molecules to the nucleus (Lys and Arg)
selective import
How are the NLS located?
nuclear import receptors
What are the steps of nuclear import?
- NLS is recognized by NIRs
- NIR bind to NLS and then that complex binds to the NPC proteins that are on the fibrils via FG repeats
- receptor travels through the pore complex with the help of Ran-G(D)P
- cargo is released in the nucleus when the GTP is added to the Ran
What are the steps of nuclear export?
- NES (nuclear export signals) on molecules that need to leave
- NER bonds to the cargo present
- Ran GTP exits with the molecule and the dephospho rylation releases the package
What is a protein considered if the rate of import is greater than the export?
a nuclear protein
