Lecture 11: intracellular compartments and protein sorting Flashcards
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?
cytoplasm
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?
- allows cargo delivery from cytosol into the nucleus by binding to the import receptor and cargo protein complex
- 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
