Flashcards in Lecture 11: intracellular compartments and protein sorting Deck (27):
What is the plasma membrane?
- outer boundary of cells
- protective barrier has transporters and signaling
What is the nucleus?
- contains the genome
- principal site for RNA and DNA synthesis
Where does intermediary metabolism occur?
Where does protein synthesis, lipid synthesis, protein folding, and storage of calcium?
- endoplasmic reticulum
What are the three topological divisions of the cell?
- nucleus and cytosol
- organelles in secretory and endocytic pathways
How do cells communicate with other cells and the exterior?
- budding and fusion
Transport between what two structures requires gated transport?
- nucleus and cytosol
What is transmembrane transport?
- transport of specific proteins from cytosol across organelle membrane via protein translocators
What is vesicular transport?
membrane-enclosed transport intermediates move proteins between various compartments via vesicles
What is a signal sequence and why is it important?
- signal sequence is used to direct the movement of a peptide to certain areas.
- it is located on N or C terminus or within the protein sequence
What describes the nuclear transport?
What proteins are imported from the cytosol into the nucleus?
- RNA/DNA pol
- gene regulatory proteins
Which proteins are synthesized in the nucleus and transported to the cytosol?
What are nuclear pore complexes?
- 30 different nucleoporins arrange to provide passive and faciliated transport of molecules
How is transport facilitated by nuclearporins?
- binding of particles to fibrils extending from the nuclear pore complex
What size molecules enter the nucleus via free diffusion?
- small molecules
What size molecules enter the nucleus via active transport?
- large molecules
What is a nuclear localization signal (NLS)
- sorting signal that directs molecules to nucleus
- positively charged lysine and arginine
What is the effect of activating NLS, nuclear localization signals?
- selective import of proteins into the nucleus
What are nuclear import receptors structure and where do they bind at?
- soluble cytosolic proteins that bind to NLS
- also bind to nuclear pore complexes on fibrils extending into the cytoplasm
Where do nuclear import receptors bind on nuclear pore complexes?
- phenylalanine glycine repeats (FG)
What mechanics are used for nuclear export and what is the sequence these proteins do this in?
- nuclear export signals and receptors
- bind, dissociate and re-bind
What are the effects of Ran-GTP binding?
1. allows cargo delivery from cytosol into the nucleus by binding to the import receptor and cargo protein complex
2. allows formation and migration of export signal protein to the cytosol from the nucleus. Hydrolysis of GTP allows off-loading of the cargo in the cytosol
What happens if proteins contain both the nuclear export signal and the nuclear localization signal?
- protein is shuttled back and forth between the nucleus and cytosol
What are the mechanisms that control the cargo transport in or out of the nucleus?
- inhibitory protein binding
If cholesterol is high, what is the following pathway and result?
- cholesterol binds with SCAP blocking SREBP and blocking biosynthesis of cholesterol
- cholesterol production is reduced