intracellular trafficking Flashcards
Where does the synthesis of all proteins begin?
free ribosomes
What determines the outcome of a protein?
It’s destination?
Cotranslational translocation
WHILE proteins are translated on membrane bound ribosomes, they are translocated into the ER lumen
Posttranslational translocation
AFTER proteins are translated on free ribosomes, they are then translocated into the EU lumen (most common in yeast)
define intracellular trafficking
the movement of materials, especially proteins, from compartment to compartment within the cell and the external environment via membrane bound vesicles
What does the word “balance” mean in relation to endo/exocytosis?
Because these transport processes require using vesicles made from the phosophlipid bilayer, a balance has to be struck in order to maintain the unit cell membrane
Endocytosis: name the kinds
Fluid phase and receptor-mediated endocytosis
fluid-phase endocytosis
non-selective
forms vesicles containing extracellular fluid + contents
receptor-mediated endocytosis
Receptors aggregate in patches on the extracellular surface of the cell membrane
Receptors associated with “coated pits” either before or after the binding with their ligands
“coated pits”
protein coating the cytosolic side of the membrane: coats the vesicles
What is the functional role of the coat?
Helps the recruitment of molecules for transport
Anchors transmembrane receptors at the site of the forming vesicle
“coated pits” coating = ?
clathrin and dynamin
T/F
a receptor MUST associate with a “coating” BEFORE it receives a shipment?
F
It can associated before or after.
Clathrin: where and what
coats pits involved in SELECTIVE endocytosis
coats secretory vesicles of REGULATED exocytotic pathways
What Is clathrin exactly?
Consists of triskelion subunits which interlock to form geometric shapes
Describe the important role of clathrin in transport, the means by which is executes its task, and any relevant material it needs to complete the job (3)
1) Anchors transmembrane receptors
2) Adaptins connect the clathrin to the receptor molecules
3) Clathrin coat is removed immediately after the release of the new vesicle into the cytoplasm: this process requires ATP and HSP 70
How does clathrin anchor to receptors?
Adaptins connect the clathrin to the receptor molecules
T/F Clathrin activity is present in places other than the cytosolic wall of the cell membrane. If so, where?
T, Golgi bodies for instance
A swastika missing a leg. What protein mildly resembles that? why?
clathrin: it’s a structure with “triskelion” subunits
Triskelion. What?
the subunits composing clathrin
Two molecules involved with clathrin…
ATP and hsp 70
hsp 70
along with ATP, involved in removing clathrin coat after the release of vesicles into the cytoplasm
keeps cleaved polypeptide (the signal sequence) unfolded so it can enter the channel
Coatamers
Coats vesicles being transported between Golgi stacks (COPI)
coats vesicles being transported from to CGN
Exocytosis pathway involves the following
begins in the ER, followed by the Golgi, and ends on the cell surface
The secretory pathway involves what?
begins in the ER, followed by the Golgi, and ends on the cell surface
The endocytotic pathway involves
1) internalization of materials from the extracellular environment by endosomes
2) degradation of materials by lysosomes
What must happen before a coated vesicle can fuse with the receptor membrane?
the vesicle has to shed its coat, which requires ATP and hsp 70
Vesicle fusion is ____ step process
2
What are the steps in vesicle fusion?
1) Recognition of the appropriate membrane SNARE-V and SNATE-t
2) Fusion of the vesicle and the target membrane NSP (N-ethylmaleimide-sensitive fusion), SNAPS (soluble NSP attachment protein)
COPI does what?
transporter BETWEEN stacks of Golgi
COPII does what?
transports from the ER to the Golgi
COP stand for
coat proteins
what do COPS form?
coatomers on the cytosolic side of a transporting vesicle
NSF and SNAPS
mediate vesicle fusion: bind to specific membrane receptors SNARES to become v-SNARES
SNARES: What and where
membrane receptors present on vesicle membranes (v-SNARES) and target membranes (t-SNARES)
also represent “docking proteins”
Docking Proteins would include which important molecules?
SNARES (v and t) that help SNAPS fuse to membranes
Vesicle Fusion (8 steps)
1) remove vesicle coat
2) binding of synapsins on spectrin
3) Binding of SNARE-v to SNARE-t
4) SNAPS bind to SNARE
5) NSF (ATPase bind to SNAP)
6) NSF/SNAP complex disassembles SNARES for reuse
7) Release of NSP and SNAP from SNARE
8) Initiation of calcium dependent membrane fusion
SNARES are _______ while SNAPS _______
docking proteins while SNAPS mediate the fusion of the vesicle with the membrane
NSFs and SNAPS differ from SNARES in that
SNAPS are the interface molecules that facilitate the fusion of the vesicles containing the docking proteins NSF and SNARES
Pathway of proteins destined for export or to be stored in lysosomes—>
- free ribosomes
- rough endoplasmic reticulum (RER)
- Golgi apparatus
- Secretory vesicles of lysosomes
Proteins containing a signal sequence attached to their N-terminal end are (a and b)
a. bound for export or to end up in lysosomes
b. have their N-terminal end cleaved off after proteins ender the lumen of the ER
All protein synthesis___
begins on free ribosomes
Signal Hypothesis: the signal is made from __ and synthesized ____
amino acids (obviously) and synthesized first.
Signal Hypothesis claims a signal sequence contains
20 amino acids and hydrophobic residues
SRP
signal recognition particle. attaches to signal sequence and prevents further elongation
attaches to sequence as it emerges from ribosome
SRP: consists of….
six proteins, 7S segment of RNA
SRP+protein+ribosomes——>binds to
a docking protein on the cytoplasmic face of the ER
SRP inserts what and where
releases protein, inserts self into membrane channel (translocon)
translocon….consists of….
translocon consists of three transmembrane proteins (Sec61 proteins)
sec61 proteins
three transmembrane proteins
BiP
another Hsp70: pulls the polypeptide chain through the channel into the ER lumen
a sugar chain is attached to an asparagine residue
this is N-linked glycosylation, last part of the signal hypothesis pathway
OVERALL idea/steps about signal hypothesis (unfinished because of complexity, but name some events)
1) a free ribosome is producing a new peptide
2) the peptide has a “signal sequence” containing about 20 amino acids and some hydrophobic residues
4) SRP binds to the sequence
5) the signal contains a message for the ribosome to connect to the ER
5) the SRP, peptide, and ribosome connect to a docking protein (SRP receptor) on the face of the ER
6) the signal sequence is cleaved
the ER consists of
a bilipid-layer membrane CISTERNAE/TUBULES/VESICLES
Cytoplasm in the ER
divided into
luminal (endoplasmic) compartment
cytoplasmic (cytosolic) compartment
subdivision of the ER has ___ subcategories which include
- Smooth ER (without ribsosomes, attached to the cytoplasmic face)
- Rough ER with ribosomes attached to the cytoplasmic face
- Transitional ER where vesicles exit to the Golgi apparatus
