Intracellular Trafficking Flashcards
Proteins being translated on membrane bound ribosomes and then translocated into the ER lumen describes
Co-translational translocation
Synthesis of all proteins begins?..
On free ribosomes
Proteins being translated on free ribosomes and then trans located into the ER lumen describes?
Post-translational translocation (more commonly in yeast)
Define intracellular trafficking?
Movement of material, mainly proteins, from compartment to compartment within the cell and to and from the external environment via membrane bound vesicles.
Non selective endocytosis that forms vesicles with extra cellular fluid and its contents.
Fluid phase endocytosis
Ligand binds with a receptor along the cell membrane
Receptor mediated endocytosis.
Clathrin has a role in both endo- and exo-cytosis. What is it?
Coats pits involved in selective endocytosis
Coats secretory vesicles of regulated pathway for exocytosis
The process of removing the Clathrin coat immediately after the release of the new vesicle into the cytoplasm requires what?
ATP and Hsp70 (heat shock protein)
This type of coatamer coat vesicles transported from ER to CGN
Cop II
Cop I coatamers coat vesicles transported between?…
Golgi stacks
Vesicle fusion is a two step process. What are the steps?
1) recognition of the appropriate membrane
snare-v and snare-t
2) fusion of the vesicle and target membrane.
* NSF
* SNAPS
List the 8 sequence of events in a vesicle docking
Biggest crock of shit thus far
1) removal of the vesicle coat
2) binding of synapsins and spectrin
3) snare v binds to snare v
4) snap binds to snare
5) NSF bind to snap
6) NSF/snap complex disassembles snare for reuse
7) release of NSF and snap from snare
8) initiation of calcium dependent membrane fusion
* requires fusigen
Proteins that are destined for export from the cell or are destined to be stored in lysosomes utilize the following pathway?…
Free ribosomes> RER> Golgi> secretory vesicles or lysosomes.
What’s the first part of the protein to be synthesized?
The signal sequences consisting of 20 amino acids and includes a stretch of hydrophobic residues
What’s the role of the signal sequence?
To direct the ribosomes to attach to the ER membranes.
What attaches to the signal sequence to prevent any further elongation?
A signal recognition particle (SRP) made up of six proteins and a 7s segment of RNA.
When does protein elongation resume?
Once the SRP docks with its like receptor, the signal sequence is inserted in the translocon membrane channel where it is released following cleavage of the signal sequence by a signal peptidase.
What is a translocon?
three transmembrane protein complex.
What does HSP (70) function in? And what is another name they go by?
HSP (70) keeps the polypeptide chain unfolded so the signal can enter the channel.
Protects the cell from high temperature
Directs folding of proteins
Chaperone protein
Clathrin consists of what kind of subunits to form geometric shapes?
Triskelion
BiP aids in what? And they are a type of what kind of protien?
The folding and assembly of multisubunit proteins.
Heat shock protein
The sugar chain, which is linked by (?), to the asparagine residue was initially attached to the luminal face of the ER by (?)
N-linked glycosylation
A lipid carrier dolichol phosphate
The cytoplasm of the ER consists of two compartments?…
Luminal (endoplasmic) compartment
Cytoplasmic (cytosolic) compartment
The ER is divided into three compartments. What are they and their function?
Smooth ER- detoxifies toxins and for lipid synthesis. Without ribosomes on the cytoplasmic face
Rough ER- synthesis of proteins. Has ribosomes on the cytoplasmic face
Transitional ER- where vesicles exit to the Golgi apparatus
This leaflet faces the cytoplasm of the cell
Protoplasmic leaflet
This leaflet faces the lumen of the ER
Exocytoplasmic leaflet
Proteins targeted for the nucleus, mitochondria, or perioxisomes are synthesized on?…
Free ribosomes and then released into the cytosol
Proteins for secretion or targeted to the Golgi, lysomes, ER, or PM are synthesized on?…
Ribosomes bound for the RER
Proteins targeted to lysosomes, secretion, or Golgi apparatus are transported in vesicles that bud off?…
The transitional ER
Proteins that are destined to be attached to the PM have what attached to their carboxyl end? Where will they face?
GPI (a really long word) anchors. Luminal leaflet on the outside of the cell
What directs correctly folded proteins to the transitional ER?
A folding sensor
A folding sensor will add a glucose residue to the misfolded protein and send it where for another attempt at folding?
Calreticulin (a chaperone )
Severely misfolded proteins at sent back through the translocon and are degraded in proteosome a located?…
In the cytoplasm
Where are phospholipids synthesized and what does it mean for any new phospholipids?
On the cytosolic side of the ER from glycerol. And can only be added to the cytosolic leaflet.
Phospholipids that are TO BE located on the luminal side of the ER are transferred via?…
Flippase proteins
What are the two faces of the Golgi?
Cis-entry
Trans-exit
What are the four functions of the Golgi apparatus?
- modifications of carbohydrates (glycosylation)
- sorting of cargo to cell destination weddings
- synthesis of sphingomyelin and glycosphingolipids
- o linked glycosylation (addition of carbs to Ser and Thr)
What is anterograde trafficking?
Vesicles carrying cargo in the cisternae from the Cis to the trans face.
What is retrograde trafficking?
Cis face back to the Rough endoplasmic reticulum
What are the two types of secretory pathways?
Facultative and constitutive
Describe facultative secretion?
Cargo stored in vesicles and only released in t cytoplasm in response to extracellular signals.
Ex: neurotransmitter or hormone
Describe constitutive secretion?
Cargo is secreted continuously without the need of an extra cellular signal.
- Includes newly synthesized lipids
- Proteins to the PM
- Proteins of the EC matrix
What is the targeting signal for lysosomal pathways?
Mannose-6-phosphate
Mannose 6 phosphate residues become what?
Acid hydrolases
Residues are …. To protect them from being removed by enzymes in the CGN
Phosphorylated
TGN jam packs all the phosphorylated M6Pases into transport vesicles and surrounded with what as it exits the Golgi?
Clathrin
Clathrin is immediately shed after it exits the Golgi in order to bind to other…
Somal bodies (endosomes, phagosomes, etc…) already in the cytosol.
Identify the five types of lysosomes
- Primary-just buds off the TGN.
- Secondary- primary fuses with a fagosome and filled with protons (hydrogens) to create a pH of 5
- Residual body-reminents of a secondary lysosome with undigested material
- Early-endocytic vesicle with internal pH mMof 7.35
- Late-endocytic vesicle fused with a lysosome with pH of 5
Residual bodies may be eliminated by?…
Exocytosis
Proteins destined for the nucleus contain what type of signal? And describe the signal
Nuclear localization signal.
Consists of 4-8 amino acids with positive charged residues. Components of the nuclear pore complex recognize the signal and position it for import into the nucleus.
T/F NLS is removed after import.
False. It can be used to recycle the protein
What marks proteins for transport into the mitochondria?
N-terminal signal sequence.
Positively charged amino acids with proceeding polar and non polar residues.
A mitochondrial signal sequence may direct proteins to specific compartments within the organelle. What are the compartments?
Outer membrane
Inter membrane space
Inner membrane
Matrix
Prior to import into the mitochondria, proteins are maintained in a partially unfolded state by this chaperone protein?
HSP 70
Where does the signal sequence bind to on the mitochondria?
A receptor on the outer membrane
Proteins in the mitochondria are transferred across both outer and inner membranes into the matrix via?
TOM complex with the usage of ATP.
What is another chaperone protein that helps assist the final folding of a protein once it reaches it’s destination in the mitochondria?
HSP 60
Let’s get in the mindset of micro tubular transport to the axon. Going from the cell body to the axon terminus involves?
Anterograde and involves kinesins
Let’s go back from the axon terminus to the cell body? What’s involved in that?
Retrograde and involves cytoplasmic dynein
There are five motor proteins. What are they? We will discuss each of them after. So just name them for now.
Kinesins, cytoplasmic dynein, myosin (I, II, V)
Myosin II is a conventional motor protein. Tell me about it.
Found in both muscle and non muscle cells
ATPase head
Paired molecules liked by tails
Binds to actin
Moves towards the plus end of actin.
Myosin I is an unconventional motor protein. Tell me about it.
Found in all cell types
Single ATPase heads binds to F actin
Tail binds to cell membranes of vesicles
Moves toward plus end of Actin
Myosin V is an unconventional MP. Tell me more.
Two heads and double tail
Found in all cell types
Head binds to F actin
Tail binds to cell membranes of vesicles
Moves towards the plus end of actin
Found in all cell types, two heads bind to microtubules, tail binds to cell membrane of vesicles, moves towards “PLUS +” end of microtubules. What am I?
Kinesin
Moves towards the MINUS - end of microtubules?
Cytoplasmic dynein
