Lecture 11: intracellular compartments and protein sorting Flashcards Preview

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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
- mitochondria


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?

- gated
- bidirectional
- selective


What proteins are imported from the cytosol into the nucleus?

- histones
- RNA/DNA pol
- topoisomerases
- gene regulatory proteins


Which proteins are synthesized in the nucleus and transported to the cytosol?

- tRNA
- mRNA


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?

- phosphorylation
- proteolysis
- 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


If cholesterol is low what is the resulting pathway and result?

- SCAP and SREBP are not bound/blocked which lead to cleavage at site 1 and 2 proteaese. this releases a factor that binds and induces cholesterol biosynthesis enzymes.
- results in production of cholesterol.