1.9: Protein Sorting Flashcards
what features are specific to animal cells and what do they do
ecm (extracellular matrix): specialized material outside of the cell
lysosome: degradation cellular component that no longer necessary
what features are specific to plant cells and what do they do
chloroplasts: photosynthesis
vacuole: 2 types: storage and the other functions similarly to the animal lysosome
cell wall: tough protective outer coat
state the 2 processes of protein sorting
- post translational process
- co translational process
describe the post translational process of protein sorting
proteins fully synthesized in the CYTOSOL before sorting. the unfolded goes to mitochondria and plastids and folded foes to nucleus and peroxiomes
describe the cotranslational process of protein sorting
happens in the ER, has proteins with er signal sequence (associated w er during protein synthesis)
list the 3 sorting mechanisms of protein
gated transport, transmembrane transport (req prot translocators), vesicular transport
which of the protein sorting mechanisms is restricted to one way
transmembrane transport
gated transport involves protein moving between ? and which complex
involves proteins moving between cytosol and nucleus
involves the nuclear pore complex (NPC) which facilitates the selective transport of macromolecules and free diffusion of small molecules (<5000 daltons)
t/f the npc can transport in both directions
true. nuclear import dictates from cytosol to nucleus and export is from nucleus to cytosol
what is the npc made up of
nucleoporins
describe the process of nuclear import
involves the nuclear import receptor which binds to NLS (rich in lys and arg) and binds to nucleoporins in npc, facilitates transport into the nucleus.
cargo proteins have the nuclear localization signal (NLS)
the nuclear import adaptor protein has _______ <– and is the blank the same for all proteins
the nls, no the nls is not the same for all cargo proteins
describe the process of nuclear export
involves nuclear export receptor, which is structurally related to the nuclear import receptor, binds to nuclear export signal (NES), binds to nucleoporins in the npc, transport into cytosol
cargo proteins have a NES
which are common molecules that have a NES (3)
newly assembled ribosomal subunits, rna, proteins w regular nuclear import and export
ran gtpase cycles between ____ bound and _____ bound
gtp and gdp bound
what is ran gtpase regulated by?
- rap gap (gtpase- activating protein): stimulates gtp hydrolysis by ran
- ran gef (guanine nucleotide exchange factor): promotes exchange of gdp for gtp by ran
what ratio is critical for direction of transport
[ran gtp] in nuclear; [ran gtp] in cytosol
(high; low)
ran-gap is in the ________
ran-gef is in the _________
high [ran-gtp] in the nucleus; low [________] in the cytosol
ran-gap is in the cytosol
ran-gef is in the nucleus
high [ran-gtp] in the nucleus; low [ran-gtp] in the cytosol
how does ran gtpase move between the nuclear and cytosol
- ran-gtp to cytosol with nuclear import/export receptors
- ran-gdp to nucleus, transported by ntf2 (nuclear transport factor 2)
detail the steps of nuclear import of cargo proteins
- nuclear import receptor binds cargo in cytosol
- receptor + cargo move to nucleus
- ran-gtp binding causes cargo release
- empty import receptor + ran-gtp move to cytosol
- ran binding protein and ran-gap promote gtp hydrolysis and release of import receptor
detail the steps of nuclear export of cargo proteins
- nuclear export receptor binds ran-gtp and cargo in nucleus
- receptor and cargo and ran-gtp move to cytosol
- ran binding protein and ran-gap promote: gtp hydrolysis, release of cargo, release of export receptor
- empty export receptor returns to nucleus
describe nfat (nuclear factor of activated t-cells) as an example of nuclear import and export regulation
high [ic ca2+] –> nuclear import
low [ic ca2+] –> nuclear export
import: calcineurin (protein phosphatase) removes pi from nfat, blocked NES and the lack of pi exposes the nuclear import signal, activation of gene transcription
export: the calcineurin leaves, atp + active protein kinase phosphorylates nfat and changes its conformation to expose the nes so it goes to cytosol
describe an experiment that you can do to observe nfat transport (gated transport)
- express nfat-gfp fusion protein in t cells
- add calcium ionophore
- monitor fluorescence
where is transmembrane transport involved it and what protein is needed
- er, mitochondria, plastids, peroxisomes
- protein translocators: transport of protein across membrane, protein usually unfolded
how do proteins remain in cytosol
by association with hsp70 chaperones
mitochondria and chloroplasts have their own genome and ribosomes but most of their proteins are nuclear encoded - where are these translated and what are its features
translated in cytosol, imported into organelle through post translational means and the protein is unfolded
are proteins unfolded or folded when they go to mitochondria and chloroplasts through transmembrane transport
unfolded
describe how to import proteins to the mitochondrial matrix
protein translocators: TOM (think of it as Translocase of Outer Membrane) and TIM23 (Translocase of Inner Membrane) complexes
- precursor protein has a mitochondrial signal sequence (peptide) with a specific n-terminal amphipathic a-helix
- it binds to receptor -> moves through TOM and TIM23 complexes into matrix space where the signal seq is cleaved
- proteins can also be further sorted
describe how to import proteins to the chloroplast
protein translocators in chloroplast membranes
- precusor protein has a chloroplast signal seq with a specific n terminal amphipathic a helix
- signal seq cleaved in chloroplast
- different from mitochondrial signal seq for correct targeting in plants
what is unmasked when chloroplast signal seq is cleaved
hydrophobic thylakoid signal sequence
describe how to sort a protein into peroxisomes
- precusor protein has a peroxisomal targeting signal
- 3 aa at c-terminus (SKL)
- protein is post translationally folded
- transported across membrane by large translocator complex
for the following destinations, state the mechanism, signal, and whether the protein is folded before transport:
i. nucleus
ii. mitochondria
iii. peroxisomes
iv. chloroplast
i. nucleus: gated, nls rich in lys and arg, folded before transport
ii. mitochondria: transmembrane, amphipathic a helix, not folded before transport
iii. peroxisomes: transmembrane, SKL at 3 terminus, folded before transport
iv. chloroplast: transmembrane, N-terminal amphipathic a helix, not folded before transport
