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Cell Physiology: Chapter 15: Intracellular Compartments and Transport


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Endomembrane Components
Er, Golgi, Transport Vesicles, Endosomes, Lysosomes, Vacuoles
Three Possible Mechanisms of Protein Transport in the cell?
1. import into nucleus via nuclear pores

2. import into organelle via protein translocator (mitochondria, chloroplasts, peroxisomes)

3. transport through compartments of the endomembrane system in vesicles
What regulates passage of materials into and out of the nucleus?
Signal Sequence which directs protens to the correct location and enables a proten to pass through nuclear pores.
What materials enter the nucleus?
nuclear proteins from the cytosol
What materials leave the nucleus?
mRNAs, tRNAs, and ribosomal subunits are transported from the nucleus to the cytosol
What materials both enter and leave the nucleus?
snRNAs move in both directions
Describe the nuclear pore complex.
-single hela cell
-imports 560k ribosomal proteins and exports 14k ribosomal subunits per minute
-octagonals symmetry (30-50 proteins)
What are nucleoporins?
the 30-50 proteins that make the octagonal symmetry of a nuclear pore complex.
Where is the nuclear pore complex found?
penetrates the inner and outer nuclear membranes
Nuclear Localization Sequence
-necessary and sufficient for nuclear targetting
-directs proteins to correct locations
-stretch of AA (one or two short stretches of positively charged AA --arginine (R), lysine (K), histidine (H))
-enables proten to pass through nuclear pores

i.e. w/out sequence, protein remains in cytosol

if basic aa is replaced by nonpolar aa, no nuclear localization
What is the classic NLS from SV40 T antigen?

basic/positive charge
Exportins, Importins?
export and import into nucleus
family of proteins function as transport receptors
How do proteins enter the mitochondria and chloroplasts?
proteins unfold as they enter
Signal Peptidase
cleaves signal sequence
addition of carbohydrate residues
Molecular Chaperones (Bip)
assist in folding
Protein Disulfide Isomerase
formation of disulfide bonds
Where does protein glycosylation occur?
In the ER

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