Protein/Endo Trafficking Flashcards
Three domains of the endoplasmic reticulum
1) Smooth ER
2) Rough ER
3) ERGIC
What is the characteristic function of the smooth ER?
lipid metabolism
What is the characteristic aspect of the rough ER?
covered by ribosomes
What does ERGIC stand for?
ER-Golgi Intermediate Complex
How is the golgi apparatus’ structure characterized?
stacked and polarized cisternae
Where does the cis face of the golgi apparatus face?
Endoplasmic reticulum
What does topology of the secretory pathway refer to?
Shit that is facing the cytosol continues to do so throughout the various fusions, etc.
Protein synthesis by free cytosolic ribosomes leads to what type of translocation?
Post-Translational Translocation
Protein synthesis by membrane-bound ribosomes leads to what type of translocation?
Co-Translational Translocation
Transmembrane proteins must use which method of translocation?
Co-translational translocation
What binds the signal sequence translated first in the beginning of co-translational translocation?
Signal Recognition Particle (SRP). Brings it into the SRP receptor on the ER membrane.
What does the ribosome bind to on the ER membrane in co-translational translocation?
Translocon
Which enzyme cleaves the signal sequence of the growing polypeptide in co-translational translocation?
Signal peptidase
What are the heat shock proteins involved in post-translational translocation?
Hsp 70 and Hsp 40. They maintain the protein in an unfolded state.
What recognizes the signal sequence in post-translational translocation
Sec62/63
What is the name of the ER chaperone which holds proteins unfolded until the whole thing passes through in post-translational translocation
BiP
An oligosaccharide synthesized on a lipid carrier. Prevents protein aggregation in the ER, which helps sort signals.
N-linked glycosylation
Which terminus are glycolipids added on to create a GPI anchor and attach proteins to the membrane?
C-terminus
What is the cytosol-side peptide signal for transmembrane proteins?
2 methionine
What is the cytosol-side peptide signal for lumenal proteins?
2 glutamic acid
What is the cytosol-side peptide signal for GPI-anchored protein?
2 aspartic acid
Specialized region of the ER where proteins and phospholipids are exported in vesicles
ER Exit Site (ERES)
What makes up the signals that direct proteins packaged for vesicle transport?
peptide and carbohydrate signals
Unmarked proteins in the ER can also be packaged and transported where by a “default pathway”?
Golgi
Proteins destined for retrieval by the endoplasmic reticulum have which two targeting sequences at their C termini?
KDEL or KKXX (there’s then a KDEL receptor)
What two important membrane components are synthesized mostly in the golgi apparatus?
Glycolipids and sphingomyelin
Four regions of the Golgi apparatus
1) cis compartment
2-3) medial and trans compartments
4) trans golgi network
Region of the golgi apparatus which receives molecules from the ERGIC
cis compartment
Region of the golgi apparatus which is responsible for most modifications
medial and trans compartments
Region of the golgi apparatus which is the sorting and distribution center
trans-golgi network
Golgi protein movement theory in which transport vesicles carry proteins between cisternae
stable cistarnae model
Golgi protein movement theory in which proteins are carried within the cisternae, which gradually mature and progressively move through the golgi in the cis to trans direction
cisternal maturation model
Which carbohydrates, added to proteins in the ER, are modified in the golgi?
N-linked oligosaccharides
In the golgi apparatus, what can mannoses be swapped out for?
1) NAG
2) galactose
3) sialic acids
What sugar can be added to the origin N-acetylglucosamine in the Golgi apparatus?
Fucose
What phosphorylated sugar signals for proteins to go to the lysosome in the trans golgi network?
mannose-6-phosphate
Carbohydrates added to the side chains of serine and threonine, creating proteoglycans, are called….
O-linked glycosylation
Three routes to go from the Golgi to the cell surface
1) direct transport to the plasma membrane
2) recycling endosomes
3) regulated secretory pathways
What sort of vesicle are hormones and neurotransmitters packaged in the trans-Golgi for regulated release
secretory granules
The three types of vesicle coat proteins
1) COPII-coated vesicles
2) COPI-coated vesicles
3) Clathrin-coated vesicles
Which family of vesicle coat proteins carries proteins from the ER to the ERGIC and on to the golgi apparatus?
COPII-coated vesicles
Which family of vesicle coat proteins bud from the ERGIC or Golgi and carry their cargo back, returning proteins to earlier compartments
COP1-coated vesicles
Which family of vesicle coat proteins transport in both directions between the trans Golgi network, endosomes, lysosomes, and the plasma membrane
Clathrin-coated vesicles
mnemonic: “two steps forward, one step back”
COPII = anterograde transport COPI = retrograde transport
Which small GTP-bind proteins, related to Ras and Ran, regulate the formation of coated vesicles
ARF1 and Sar1
What two things mediate interactions between transport vesicles and target membranes?
tethering factors and Rab proteins (small-GTP binding proteins)
What protein on the vesicle drives fusion?
vSNARES
What protein on the target membrane drives fusion?
tSNARES
What is the motor protein involved in membrane fusion?
Dynamin
What does Rab bind on target membranes?
Tethering factors
What binding motif do SNARE proteins have?
central coiled-coil domain
What is the ideal pH for most of the lysosomal enzymes which are called “acid hydrolases”
5
How is a lysosome formed?
A transport vesicle fuses with a late endosome
They fuse with endocytic vesicles from the plasma membrane in order to separate molecule for recycling from molecules destined for degradation in lysosomes.
Early endosome
Molecules to be recycled are passed to these and back to the plasma membrane
Recycling endosomes
Carry molecules to be degraded by lysosomes
Late endosomes
Phagosomes fuse with lysosomes to become…
phagolysosomes
Mechanism for selective uptake of specific macromolecules
Clathrin-mediated endocytosis
Specialized region where macromolecules can bind to cell surface receptors
clathrin-coated pits
Endocytosed (is that a fucking word) clathrin-coated vesicles then fuse with what?
early endosomes
What causes receptors and ligands to separate in early endosomes?
acidic pH (6.0 - 6.2)
Examples of clathrin-independent endocytosis (3)
1) macropinocytosis
2) internalization of caeolae
3) uptake of GPI-anchored plasma membrane proteins clustered in lipid rafts
What does LDL stand for
Low-density lipoprotein
LDL / clathrin coated pit dysfunction where either the receptors don’t bind LDL or the mutations prevent the receptors from concentrating in the coated pits
Familial hypercholesterolemia
The six amino acid signal, including tyrosine, which prevents LDL receptors from concentrating in coated is called what
internalization signal
What does CEDNIK syndrome stand for?
Cerebral dysgenesis, neuropathy, ichthyosis, and palmoplantar keratoderma
What is the inheritance pattern of CEDNIK syndrome?
autosomal recessive
What is mutated in CEDNIK syndrome?
SNAP29 (part of the SNARE complex)
I-Cell Disease is also referred to as…
mucolipidosis II
Which gene is mutated in I-cell disease?
GNPTAB (chromosome 12)
GNPTAB gene (well the protein it codes) is the first step in what process?
tagging lysosomal enzymes with mannose-6-phoasphate in the golgi apparatus
Coarse facial features, joint limitations, skeletal abnormalities, cardiomegaly, developmental delay, and early loss of life…
I-cell disease
