Flashcards in Intracellular Compartments And Protein Sorting I Deck (36):
What is the principal site of DNA and RNA synthesis?
What does the cytoplasm consist of?
Cytosol and cytoplasmic organelles
What is the site of protein synthesis, lipid synthesis, protein folding and storage of calcium?
Where is the site on which post-translational changes on proteins and lipids occur?
What is the site of ATP production, signaling, cell differentiation and death?
What organelle contains digestive enzymes that degrade organelles and biomolecules?
What organelle is a small vesicular compartment that contains enzymes used in oxidative reactions?
What are the three topological categories of the cell?
Nucleus and cytosol
How do the lumen of the nucleus, cytosol, etc. communicate with each other and with the cell exterior?
Membrane budding and fusion.
What is gated transport?
Transport between the nucleus and cytosol through nuclear pore complexes.
What is invovled in transmembrane transport?
Membrane protein translocators directly transport specific proteins from cytosol across an organelle membrane.
What is involved in vesicular transport?
Membrane-closed transport intermediates move proteins between various compartments via vesicles.
Where are protein sorting signals localized?
On N or C terminus or within protein sequences.
What enzyme may remov a signal after a protein reaches its final destination?
What are signal sequences necssary for?
What are signal sequences recognized by?
Proteins needed in the nucleus are imported from where?
Proteins are synthesized in the cytosol.
Molecules such as tRNA and mRNA that are synthesized in the nucleus are exported where?
What is the function of nuclear pore complexes?
They transport molecules from the nucleus in pot directions.
The transport is facilitated by binding of particles to fibrils extending from the NPC.
What type of transport is used in nuclear pore complexes?
Passive diffusion of small molecules and facilitated transport.
What are nuclear localization signals (NLS)?
Sorting signals that direct molecules to the nucleus. They result in the selective import of proteins into the nucleus.
What are nuclear localization signals composed of?
Short sequences rich in positively charged amino acids lysine and arginine.
What is NLS recognized by?
Nuclear import receptors (NIRs).
What are nuclear import receptors (NIRs)?
Soluble cytosolic proteins that bind to NLS on protein and to NPS proteins present on fibrils that extend into the cytoplasm.
What is found on NPS proteins that serve as binding sites for import receptors?
Phenylalanine glycine (FG) repeats.
How do receptors traverse NPC?
By binding, dissociating and re-binding to adjacent FG repeats.
What happens once receptors reach their destination (nucleus)?
Cargo is released inside the nucleus and NIR returns to the cytoplasm.
What is needed in order for molecules to go out of the nucleus?
Nuclear export signals and complementary nuclear export receptors.
What drives nuclear transport in the appropriate direction?
Gradient of Ran conformational states.
How do import receptor and cargo enter the nucleus?
By interacting with FG repeats on NPC proteins.
What occurs as Ran-GTP binds to a complex of import receptor and cargo?
The binding causes the release of cargo.
In the cytoplasm, what is Ran-GTP hydrolyzed by?
What do NLS and NES shuttle back and forth between?
The nucleus and cytosol.
What is steady state localization dependent on?
The relative rate of transport.
If the rate of import is greater an export, it is considered nuclear and vice versa.
What are the functions of gene regulatory proteins?
They keep transport stringently controlled.
They are kept out of the nucleus until needed.
Transport is controlled by NLS and NES being turned on and off. Mechanisms include phosphorylation, proteolysis, binding to inhibitory proteins.