Protein Sorting And Trafficking Flashcards
What are the 3 types of transport and name what kind of organelles are involved
1- gated transport : nuclear pore complex transport
2- transmembrane : mitochondria, chloroplasts, ER VIA TRANSLOCATORS
3- vesicular - Golgi, endosome, lysosome,
VIA CARGO EXOCYTOSIS AND ENDOCYTOSIS
What allows proteins to be transported to specific organelles due to receptors that bind to it
Proteins have a signal sequence of amino acids which bind to receptors for translocation into them
Nuclear localisation contains both import and export signals detected by receptors. What stuff is imported and exported from nucleus
Imported - transcription factors / regulators , DNA polymerase, rna polymerase
Exported - mrna , ribosomal rna , trna , Sirna
What on the nuclear pores stop passing of large macromolecules normally such as transcription factors into nucleus
Nucleoporin channels
Explain the process of activating transcription of new Tcells from when the Tcell becomes activated
NF AT activation causes rise in calcium conc in Tcell activation
This causes calcineurin (calmodulin and calcium complex) to activate phosphatase and this de phosphorylates NF AT
This causes the import signal to be read by receptors
Imported into the nucleus
Transcription of new T cell starts
Kinase then phosphorylates NF AT again and it is exported out of nucleus
Explain the process of insertion of porins into chloroplasts/ mitochondria outer membrane
TOM complex (trans located protein) binds to signal sequence
This then translocates it into membrane
Chaperones redirect it to the SAM complex which folds the polypeptide correct
Stays in the membrane
What are chaperones for in formation of porins
Prevent aggregation of proteins
What are the events that occur when a protein wants to translocates into the matrix
TOM receptor binds to signal sequence
Translocates it through OM
The TIM complex then binds to it causing translocation into the matrix
Signal sequence cleaved
Protein stays there
What enzyme cleaved signal sequences
Peptidase
Why is the signal sequence that redirects protein to rer different
It stops translation of the polypeptide and is transported to the RER where it binds to a receptor
It it co synthesised at the rer using its ribosomes (peptidyl transferase site)
What happens to soluble proteins at the RER
The polypeptide is synthesised fully by the ribosomes
Then polypeptide enters the rer
The signal sequence is cleaved by peptidase and protein STAYS IN RER
How does the rer produce single pass transmembrane proteins
The ribosomes finish the polypeptide then it enters
The signal sequence is cleaved and the protein is inserted INTO THE MEMBRANE SINGLE PASS
It can then be glycosylated
How can GPI anchored proteins or even glycoproteins be produced at the rer AND TRANSPORTED TO PLASMA MEMBRANE
It takes the transmembrane proteins transmembrane domain and cleaves it
This allows for the GPI anchor to replace it
Vesicular transport then transports it to plasma membrane
(Normal glycoproteins just directed via vesicles)
What is vesicular transport / membrane trafficking important for
Phagocytosis / endocytosis
Exocytosis for cell communication/signalling
What are the 3 vesicular pathways
1- endocytic (to endosomes and lysosomes)
2- secretory - out to plasma membrane
3- retrieval - from the plasma membrane in
What are the 3 protein coats and where are they found
Cop I - found at RER
Cop II found at Golgi cisternae
Clathrin - membrane, endosomes, lysosomes (endocytosis pathway)
What are lysosomes / lysozymes
Organelles containing acidic / hydrolases enzymes
Degrade endocytosed material
How is the acidic ph of lysosomes maintained
ATPase H pump
Explain the path of endocytosis
Vesicle transports to endosomes both early and late
Then produce an endolysosome where degraded
Explain the path of phagocytosis (lysosome pathway)
Material engulfed/bacteria.
Forms a phagosome
Phagosome forms a phagolysosome with a lysosome
Hydrolysed material
What other 2 pathways other than endocytosis and phagocytosis are there in degradation
Macropinocytosis- uptake of non specific fluids or material into cell
Autophagy
What is autophagy explain it
Unwanted proteins or cell debris enclosed by double membrane into an auto phagosome
Fuses with lysosome to form autophagolysosome
Hydrolysis occurs
What happens to proteins at the Golgi coming from the rer ?
Glycosylation / addition of oligosaccharides
What receptor on the trans face of Golgi causes vesicular diversion to the lysosome ?
Mannose 5 phosphate receptor
This interacts with proteins glycosylated with it and causes then to move to lysosome
What is the constitutive pathway
Where budding occurs from Golgi and the new lipids and proteins are exocytosed without a signal needed
What is signal mediated exocytosis
Signal such as a ligand bound to membrane allows for the vesicular fusion and exocytosis of material from the Golgi
Other than get hydrolysed by lysosomes what can endocytosed material do
Recycled back into the membrane (eg receptor mediated endocytosis takes back the receptor)
Trans cytosis into another cell
How is autophagy important for cellular survival?
It can degrade damaged proteins such as aggregated proteins which would mean in functioning cell
Are transmembrane proteins produced at the rer soluble or insoluble
Insoluble because they are hydrophobic (enter membrane)
- they have hydrophobic side chains like valine
How many membranes are in the nuclear pore complex in the nuclear Envelope
2
What is the difference between Tim 23 and Tim 22
Tim 22 inserts the proteins into the inner membrane
Tim 23 the soluble proteins stay inside the matrix
Are proteins unfolded or folded when translocated
Unfolded
Why are proteins produced from the er glycosylated
To make sure they fold properly if chaperones allow aggregation or misfolding
