Chapter 8: endomembrane system Flashcards
biosynthetic pathways:
pathway where proteins are synthesized in the ER, modified in the golgi, and transported to other parts of the cells
secetory pathway
when proteins are discharged from the cell (from their secretory granules) into the extracellular comparment
constitutive secretion
material are discharged in a continual manner
when materials are stored in vesicles and secretory grandules and only discharged in response to a certain stimulus
regulated secretion
endocytic pathways
routes where external materials can enter the cell. frlow from the cell surface to the interior by way of endosomes and lysosomes.
how does cargo follow different pathways to different locations?
via amino acid coding signals or oligosaccharide coding signals.
An experiment that is an example of how autoradiography and electron microscopy can be used to study endosomes
a pulse chase experiment. Pulse amino acids with radiation and allow them to be taken up by the cell. After a few minutes/hours, see where they are in located in the cell “chase” to see which organelle theyre in.
the longer the chase, the further the proteins will be from the starting point (ER)
Autoradiography
a method to visualize biochemical processes using radioactive labelled Amino acids exposed to a silver photographic film.
Purpose of using GFP.
tagging GFP with a protein of interest allows the protein to emit fluoresence when created.
when the DNA for GFP and a different protein get coupled, this is called the
GFP-DNA chimera
How do you find and mark organelles to see where the GFP protein is truly located in the cell?
use mannosidase to tag the golgi, the dye is specific to golgi. if GFP and red dye overlap, you know that the protein is in the golgi.
Methods of homogenization
1) homogenizer
2) chemical lyses
3) mortar and pestle
4) glass beads
Using differential centrifugation and subcellular fractionation to study a specific organelle is an example of a
cell free system
microsomes
membranous vesicles derived from the endomembrane system (primarily the ER and golgi), some lysosomes and peroxisomes.
how would you separate the smooth and rough ER?
1) homogenization of ER
2) smooth and rough ER particle solution is placed in tubes with increasing sucrose solution
3) centrifugation
in a tube with LOW levels of sucrose: smooth Er will be in supernatant, and rough ER will be in pellet
in a tube with HIGHlevels of sucrose: smooth ER will be in the pellet and the RER will be in the supernatant.
isopyric point
region in the sucrose gradient tube where the density of the fraction = the density of sucrose (the ER microsome)
the determination of different genes that are involved in vesicular formation and the endomembrane system can be studied by:
using mutant phenotypes in an experiment
SEC12 gene:
allows for vesicles to bud off from the endoplasmic reticulum.
What would happen if you had a mutated SEC12 gene?
proteins would stay in the ER because they could not bud off, ER would swell
SEC17 gene
allows for fusion of vesicle to the golgi complex
what would happen in if you had a mutated SEC17 gene?
Vesicles would pinch off from the ER and would stay in the cytosol because they would not fuse with the golgi
How does the use of RNA interference through siRNAs affect protein translation?
siRNAs will INHIBIT translation of mRNA to protein by blocking and binding with mRNA, making mRNA appear to the ribosome as double stranded. tRNA cannot interacti with mRNA if it is hybridized with siRNA, and thus no proteins can be synthesized.
using siRNAs to stop translation produces a temporary effect called _______
protein knockdown
the network of flattened sacs of the ER is called
cisternae
what proteins make the SER so much curvier than the RER?
reticulon proteins help curve the SER tubules
three main functions of SER
1) steroid synthesis
2) detoxification in the liver via oxygenases
3) sequesters Ca2+ ions in muscle cells
After a protein leaves the golgi in a vesicle, what are it’s three fates?
1) fuse with the plasma membrane and the contents get exocytosed into the extracellular space (secreted)
2) become an integral membrane protein
3) be released in the cytoplasm of cell as lysosomes or digestive enzymes
in an epithelial cell, the ER is located at the ____ side of the cell, and mucus vesicles move upwards towards the ____ side of the cell so that mucus can be secreted into the lumen. this is an example of organelle _____
in an epithelial cell, the ER is located at the BASAL side of the cell, and mucus vesicles move upwards towards the APICAL side of the cell so that mucus can be secreted into the lumen. example of organelle structural polarity.
organelle thats thte starting point of the biosynthetic or secretory pathway
RER
Types of proteins made in the RER
1) secreted proteins
2) integral membrane proteins
3) soluble proteins that are invovled in the endomembrane system (ex/ resident proteins) or as lysosomes or in plant vacuoles
Types of proteins made by free ribosome
essentially, proteins that are released directly in the cytosol ( no vesicles like secretory proteins)
1) proteins involved in glycolysis
2) peripheral proteins
3) proteins meant to be transported into the nucleus
4) proteins to be incorporated into the peroxisomes, chloroplasts or mitochondria.
proteins made by the free ribosomes for the nucleus, peroxisomes or chloroplasts or mito are imported into their respective cells
POST translationally. (not co-translationally, like how RER proteins are synthesized)
site of synthesis (free ribosome or RER) of a protein was determiend by ____
signal sequence of amino acids on the nascent polypeptide
List the steps of how secretory, lysosomal, or plant vacuolar proteins are synthesized in the ER
1) free ribosome starts synthesizing poly peptide. The first amino acids to come out of the N terminus end is the signal sequence amino acids, which indicate that it is a secretory protein
2) an SRP (signal recognition peptide) recognizes the signal sequence and binds to the polypeptide-ribosome complex.
3) the SRP-ribosome complex binds to the SRP receptor located on the rough endoplasmic reticulum.
4) the Ribosome-polypeptide complex binds to the translocon in the ER membrane which is accompanied by GTP hydrolysis ON THE SRP RECEPTOR. The ribosome is now membrane bound and SRP is displaced once GTP is hydrolyzed.
5) the translocon plug gets displaced the memb-bound ribosome continues to synthesize and translocated into the ER lumen at the same time (cotranslationally)
6) in the lumen, the nascent polypeptide interacts with chaperone proteins like Bip to get folded correctly.
when the entire polypeptide is in the ER lumen, what enxzyme cuts off the signal sequence portion?
signal peptidase.
Signal peptidase and oligosaccharyltransferase are _____ proteins
integral membrane proteins that are associated with the translocon.
how does the RER prep and strengthen proteins (make them keep their shape) that are destined for harsher environments like the extracellular space?
protein disulfide isomerase (PDI) folds and rearranges strong disulfide bonds within the protein to maintain protein stability.
how are integral membrane proteins synthesized? How is orientation determined?
in the rough ER. uses SRP and translocons like secreotory/lysosomal/vacuolar proteins, but the polypeptide does not pass all the way through the translocon.
- translocon acts as a clamshell and pushes the protein directly into the membrane
- inner lining of the translocon orients the nascent polypeptide based on (+/-) charge.
mechanism of membrane biosynthesis
membranes arise from old membranes. membranes grow as lipids and proteins are inserted into existing membranes in the ER. membranes then bud in the form of vesicles into the golgi, and its proteins and lipid composition are modified as it moves.
where are most membrane lipids synthesized?
in the ER, except sphingolipids and glycolipids, which are synthesized in the golgi.
T/F: newly made phospholipids are only inserted into one leaflet of the membrane
true. phospholipids are inserted hald way into the bilayer that faces the cytosol, and then flippases create the opposte leaflet
purpose of lipid transfer proteins
bind onto lipids and transport the lipids through the cytosol from membrane compartment to the next. Does not invovle transport vesicles.
addition of sugars to an oligosaccharide chain is catalyzed by ______
glycosyl transferase
in order for a sugar to be added to a pre-existing oligosaccharide chain, it must:
become a NUCLEOTIDE sugar, like UDP-mannose, or UDP-Acetylglucosamine.
te arrangement of sugars on an oligosaccharide chain is determiend by:
the spatial arrangement of glycosyl transferases
In the ER, an oligosaccharide is attatched to a protein through an _____amino acid, creating an _____ linkage.
In the ER, an oligosaccharide is attatched to a protein through an Asparagine amino acid, creating an N-linkage.
the core of the carbohydrate chain made in the ER is constructed on ______, a lipid carrier
dolichol phosphate, located in the ER membrane
T/F the oligosaccharide core chain made in the ER varies between the types of protein
false. the core made in the ER is invariant.
How many sugars make the core of the oligosaccharide chain that is put onto proteins in the ER/
14 sugars. 2 NAG, 9 Mannose, 3 glucose.
process of creating the carbohydrate core and adding it to a poly peptide chain in the ER
1) 2 NAG’s in the form of GDP-NAG is transferred to dolichol phosphate one at a time
2) 5 UDP-mannose’s get transferred one at a time and get attached to the 2nd NAG on dolichol phosphate.
3) dolichol phosphate gets FLIPPED across the membrane so that the chain now faces inside the lumen of the ER.
4) 4 more UDP-mannoses get attached to the pre-existing 5 mannoses on the carb chain while in the lumen of the ER.
5) 3 glucoses get trasnfered (in the process of UDP-glc)
6) the preassembled block gets transfered from dolichol phosphate to an asparagine on the nascent poly peptide WHILE it is being transferred into the lumen on the translocon. catalyzed by oligosaccharyltransferase
when does the nascent polypeptide chain get the core carbohydrate oligosaccharide attached?
the preassembled block gets transfered from dolichol phosphate to an asparagine on the nascent poly peptide WHILE it is being transferred into the lumen on the translocon.
to undergo quality control, the glycoprotein gets 2 of the three core glucoses cleaved off and it binds to ____, and ER chaperone protein
binds to calnexin.
process of quality control in the ER
1) N linked glycoprotein gets 2 glucoses cleaved off by glycosidase
2) glycoprotein attaches to calnexin by its remaining glucose
3) if the protein is good to go, glucosidase II removes the remaining glucose and it gets packaged. If misfolded, it is recognized by UGGT, which adds another glucose back onto the protein.
4) the re-tagged protein attaches to calnexin. If it still misfolded, it will be directed to the proteosome for destruction in the cytosol.
During ER protein quality control, if the protein is good to go, glucosidase II removes the remaining glucose and it gets packaged. If misfolded, it is recognized by ____, which adds another glucose back onto the protein.
UGGT
during quality control of proteins in the ER, if the protein is repeatedly misfolded, it is taken to the _____ for destruction
proteosome.
Unfolded protein response
the accumulation of misfolded proteins triggers a genetic response to stop producing proteins all together. Due to the fact that the proteosome cannot degrade the proteins as fast as they are being made
typically, unfolded protein response sensors are being controlled by ____, but when there is too much protein being accumulated, these chaperones become too busy to control the sensors
UPR sensors are usually inhibited by Bip chaperone
2 main sensors involved in the unfolded protein response
ATF6 and PERK
how does ATF6 sensor contribute to the unfolded protein response?
- the release of inhibitory Bip chaperonse allows ATF6 to move to the golgi complex, where the cytosoic domain of ATF6 protein is cleaved from its transmembrane domain (the sensor is broken in half)
- the transmembrane portion of ATF6 moves to the nucleus where it simuluate the expression of genes whose proteins encode for alleviating ER stress, including transport vesicles and quality control machinery, and chaperone proteins.
how does PERK sensor contribute to the unfolded protein response?
- release of inhibitory Bip chaperone triggers the PERK sensor that causes the DIMERIZATION of perk.
- when dimerized, PERK becomes a PROTEIN KINASE that phosphoryalyes the eIF2alpha transcription factor, INHIBITING THE TF
- without that TF, there is decreased protein synthesis in the ER.
eIF2alpha
a transcription factor that drives the production of protein in the ER when turned on. If it gets phosphoryalted (by PERK dimer kinsases), it gets turned off and the ER no longer produces proteins on the membrane bound ribosomes
ERGIC
the endoplasmic reticulum golgi intermediate complex. Created by when transport vesicles fuse with one another to form larger vesicles and interconnected tubules in the region between the ER and the golgi.
VTC
vesicular tubular carriers. form on the ERGIC and move contents towards the golgi on a track of microtubules
how to VTCs move from the Ergic to the golgi?
on a track of microtubules
purpose of CGN on the golgi
acts as a sorting station: distinguishes between proteins to be shipped back to the ER and those that are allowed to proceed to the next golgi station
purpose of the TGN on the golgi
sorts proteins into vesicles destined for different aread os the cell.s
how is the golgi taken apart during mitosis?
via fibrous proteins
how is the golgi mechanically supported
by peripheral membrane skeleton made of spectrins and ankaryns
What compartments of the golgi does glycosylation of the protein occur?
in the cis and medial cisternae of the golgi. most of the mannoses that comprise the core are taken off and new sugars are added via glycosyl transferases.
t/f: glycosylation of proteins by glycosyl transferases in the golgi is varied between proteins
true. unlike the ER glycosylation which adds the same core to all proteins, different sugars are added to different proteins.
what part of the endomembrane system helps create complex carbohydrates?
golgi complex. can synthesize glycan, proteoglycan etc.g
glycosyltransferases are ____ proteins that face the ____ of the golgi.
glycosyltransferases are integral membrane proteins that face the Lumen of the golgi. therefor, glycosylation in the golgi takes place on the luminal face, unlike the first steps of creating the oligosaccharyl core of the ER glycoproteins, which get flipped into the lumen half way through.
cisternal maturation model
cis face portions of the golgi are formed by the fusion of vesicles from the ER to the ERGIC. each cistern matures as it moves from the cis face to the trans face
vesicular transport model
cisternae of the golgi stack remain in place as STABLE comparments, and cargo and membrane proteins are shuttled through the golgi stack in vesicles.
current model of how materials are moved through the golgi complex
kind of like the citernal maturation model, but with the belief that vesicles can also move backwards.
2 functions of the protein coat
1) act as a mechanical device that causes membranes to curve and form a vesicle
2) select the components to be carried by the vesicle.
types of proteins that are carried in vesicels
secretory, lysosomal or plant vacuolar, or membrane proteins
-proteins meant for organlles like peroxisomes, mito, etc. are not put into vesicles because they are synthesized by free ribosomes directly in the cytosol and not in the endomembrane system.
2 coats of the vesicles
1) outer scaffolding coat.
2) inner layers of adaptor proteins that selectively bind to certain substrates to concentration target molecules in the vesicle
directory of COPII protein covered vesicles.
antergrade movement. moves vesicles from the ER tot he ERGIC and Golgicomplex
proteins that are selected by COPII for vesicle formation
1) enzymes that act at later stages of the biosynthetic pathway, ex/ glycosyltransferases, which will be used in the golgi
2) membrane proteins involved in the docking and fusion of the vesicle with the target compartment
3) membrane proteins that are able to bind to soluble cargo (like secretory proteins)
Sar 1
G protein in the ER membrane that is recruited to the ER membrane in GDP form, and exchanges GDP for GTP via GEF. When GTP binds to SAR1, it undergoes conformational change and inserts its N terminus into the cytosolic leaflet to induce curvature.
What proteins are recruited to the ER membrane by GTP-SAR1?
recruits SEC23 and SEC24, which is part of the COPII coat, to form a SEC23/24 dimer and induce additional curvature to the ER membrane portion.
which portion of the SEC23/24 COPII dimer acts as a primary adaptor? what does it do?
SEC24 functions as a primary adaptor/cargo receptor that will interact with certain signals of integral membranes in order to select specific integral membrane proteins and cargo into the vesicular region.
COP II proteins _____ and ____ form a simple lattice on top of Sec 23/24 and SAR 1
Sec 13 and Sec 31 bind to the membranes to form the outer structural lattice cage of the COP II protein coat.
how and when is the COPII coat dissassembled?
COP II coat is disassembled when it reaches the destination organelle (either ERGIC or GOLGI) and is triggered by the hydrolysis of GTP from GTP-SAR1, producing SAR1-GDP, which can be recruited back to the ER membrane later on.
directory of COPI protein covered vesicles.
involved in retrograde movement. moves golgi resident enzymes in a trans to cis direction. moves escaped ER resident proteins from the golgi back to the ER.
COP I protein coats contain ____ a membrane-bending GTP-binding protein. .
ARF 1. Like the SAR 1 in COPII
GTP must be hydrolyzed before the coat can disassemble
Basis of the retention mechanism for retaining ER proteins in the ER
retention: proteins meant to stay in the ER will try and remain in the ER furing vesicle transformation based on physical properties. Soluble proteins that are a part of large protein complexes or membrane proteins that do not have cytoplasmic tails that cannot interact with COPII adaptor proteins will not be exported
proteins that are meant to be in the ER that accidentally escape into the golgi are recognized by their ____ sequences, and will be delivered back to the ER via ____ protein coated vesicles.
proteins that are meant to be in the ER that accidentally escape into the golgi are recognized by their RETRIEVAL SEQUENCES (KDEL or KKXX) sequences, and will be delivered back to the ER via COPI protein coated vesicles.
proteins that are ER lumen residents have a ____ retrieval sequence and are recognized by ____ receptors in the golgi, which shuttle them back to the ER.
KDEL sequence, recognized by KDEL receptors in the golgi.
proteins that are meant to be placed in the ER membrane rather than the lumen contain a ____ retrieval sequence
KKXX retrieval sequence.
what would happen if there was a mutation where membrane ER proteins did not have a KDEL sequence?
if they escaped from the ER, they would not be returned because KDEL retuning receptors could not recognize them
how are proteins and enzymes that are destined for the lysosome tagged in the golgi?
they are tagged with phoshphorylated mannose-6 residues in the golgi.
lysosomal enzymes are transported from the TGN in ____coated vesicles
clathrin coated vesicles.
lysosomal enzymes carrying mannose tags are captured by _____ receptors that are located in the TGN>
lysosomal enzymes carrying mannose tags are captured by mannose-6-P receptors that are located in the TGN. They are integral membrane protein.s
the outer lattice of the clathrin coat look like ____ made out of clathrin protein
honeycombs
main adaptor protein in the inner layer of a clathrin coat that is responsible for escorting lysosomal enzymes from the TGN
CGA adaptor proteins
How does the structure of CGA bind lysosomal enzymes for escort?
- outer tips of CGA (the inner clathrin coat) bind to the outer clathrin coat
- the inner CGA ends bind to the mannose-6-phosphate receptors, which are carrying the mannose-lysosomal enzymes within the lumen.
which protein helps bend clathrin coated vesicles?
ARF1 GTP-binding proteins, like COPI protein coated vesicles
SAR1 and ARF 1 are examples of _____proteins
G proteins; can bind to GTP/GDP
What happens to the clathrin coat when the lysosomal vesicle buds from the TGN?
the clathrin dissociates and the vesicle continues to travel uncoated. If the enzymes are supposed to go to the endosome or plant vacuole instead of the lysosome, the MPRs also dissociate
the movement of a vesicle to a specific target is largely mediated by ____
microtubules
the tethering of vesicle to a specific target is mediated by 2 main groups of tethering proteins:
1) rod shaped fibrous proteins, like Golgins, which can reach out and capture vesicles carrying golgi bound cargo, and form a bridge between the two membranes from relatively FAR distances
2) large, multiprotein complexes that can hold membranes at CLOSER proximity
Tethering of vesicle is mediated by _____. How are Rabs activated?
mediated by Rabs. Rabs are G PROTEINS and are activated when GTP is bound. Rabs recruit specific cytosolic tethering proteins to specific membrane surfaces. they essentially act as adaptor proteins for other tethering proteins.
After a vesicle is initially tethered, it is later docked to the target membrane. this is facilitated by ____ protiens
SNARE proteins
2 categories of SNARES
SNARES help dock the protein after Rab has initiated tethering.
VSNARE: SNARES located into the vesicles
TSNARES: SNARES located on the target membrane.
how do V and T SNARE interactions allow for vesicle docking
motifs from both SNARES form a 4-stranded bundle with 4 alpha helices, that ZIP together to form a complex that pulls the 2 opposing lipid bilayers in close association, forming a FUSION PORE.
V and T snares are capable of forming a fusion pore for the contents of the vesicles to enter the target membrane. However, something additional must happen for the fusion pore to form. What is this?
Vsnares will not fuse completely with the t snares unless a Ca2+ nerve impulse is given.
How are V and T snares released from each other?
via NSF proteins, which require ATP hydrolysis.
What is the mechanism for botulism and tetanus?
causes paralysis because it prevents V and T snares from interacting with each other. Thus, neurotransmitter vesicles cannot fuse with the target synapse.
the fusion of a secretory vesicle/granule with the plasma membrane and subsequent discharge of its contents to the extracellular space is aka
exocytosis
exocytosis is triggered by the release of:
ca2+ ions, which must bind to Ca2+ receptors on the synaptic vesicle.
lysosomes contain ____ which allows the digestion of every type of biological molecule
acid hydrolases
how is the acid environemtn of the lysosome maintained?
by a H+-ATPase V type proton pump (the enzyme uses energy from ATP but the enzyme itself does not get phoshphorylated)
the lysosomal membrane is lined with ____ to protect the membrane from its own acidic contents
lined with glycosylated integral proteins.
which organelle plays a key role in organelle turnover?
1) lysosomes
2) mitochondria
3) protesomes
4) peroxisomes
lysosomes, they engage in autophagy
autophagy
destruction of cells own organelles for replacement.
during autophagy, a tagged organelle gets surrounded by a ____, which is a double membrane structure. the organelle and ____ produces an _____, a double membrane sequestering vesicle.
during autophagy, a tagged organelle gets surrounded by a PHAGOPHORE, which is a double membrane structure. the organelle and PHAGOPHORE produces an AUTOPHAGOSOME, a double membrane sequestering vesicle.
during autophagy, the autophagosome fuses with the lysosome to form an ____, where the autophagosome is degraded.
during autophagy, the autophagosome fuses with the lysosome to form an AUTOLYSOSOME, where the autophagosome is degraded.
residual body. How might residual body be saved in the cell if it is not exocytosed?
resues that are left after the degradation of the autophagosome in the autolysosome. May be retained as a LIPFUSCIN GRANULE.
Tay Sachs disease mechanism
results from a deficiency of the lysosome that is responsible for degrading gangliosides.
substrate reduction therapy
drugs are administered to inhibit the synthesis of the substances that accumulate in the disease
T/F; a vacuole can contain things other than water and solutes
true. it can also contain toxic compounds like ACID HYDROLASES and amino acids, vacuoles can function as a plant lysosome
tonoplast
plant vacuole membrane.
a plant vacuole is acidic or basic?
acidic
how is the pH of a plant vacuole maintained?
also by a V type H+ ATPase, like a lysosome. q
Proteins in plant vacuoles are made in free ribosomes or RER ribosomes?
RER ribosomes. RER ribosomes make secretory, integral membrane proteins, or Lysosomal/endomembrane resident/plant vacuolar proteins.
a molecule of clathrin has 3 heavy chains and 3 light chains that form a ____, which accounts for the polygon network lattice of a clathrin coated vesicle
triskelion.
most common adaptor protein in clathrin coated ENDOCYTOSED vesicles (recall, CGA is a clathrin adaptor for exocytosed vesicles)
AP2.
AP2 vs CGA adaptor proteins
AP2 is present in clathrin coated vesicles that are ENTERING the cell via RME. Has multiple subunits and is located in the VESICLE and becomes part of the target membrane when it fuses.
CGA is present in clathrin coated vesicles that are LEAVING the TGA. Has a single subunit and is located in the TGA, which becomes part of the vesicle bud.
4 main subunits of the AP2 RME-clathrin adaptor protein
1) mu subunit: engages the cytoplasmic tails of the cargo and selects specific receptors and proteins into a region to form a vesicle around it.
2) beta subunit: binds and recruits the clathrin molecules of the lattice
3) alpha adaptin
4) theta adaptin.
COP II versus Clathrin outer layer (RME clathrin)
COPII outer layer: made of NON OVERLAPPING SEC13/31
Clathrin outer layer: made up of heavy and light chains overlapping to form a triskelion, responsible for geometric shape.
COP II versus RME clathrin proteins that induce curvature
COPII uses SAR1 and Sec 23/24 to induce curvature (sec 24 also acts as a primary adaptor and substrate receptor)
Clathrin uses DYNAMIN G PROTEIN to help the vesicle bud from the membrane. clathrin coated vesicles leaving the TGN also employ ARF 1
What happens if you do not allow dynamin to hydrolyze its GTP?
dynamin will continue to form a collar around clathrin coated vesicle, and it will not allow the vesicle to be relased from the plasma membrane.
How does the clathrin coat during RME dissociate once the vesicle has entered the cell?
via AUXILIN COFACTOR
2 primary groups of receptors that are subject to endocytosis
1) housekeeping receptors/LDL receptors
2) Signalling receptors
How does Lowdensity lipoprotein enter the body?
LDLs and iron are transported to the plasma membrane in a coarted pit and taken up via RME. LDL receptors are household receptors and thus the receptors are recylced back to the surface of the cell. LDL is transported to the lysosome where it can be degraded for use.
____ receptors bind extracellular ligands that carry messages to change the activites of the cell.
signalling receptors.
signalling receptors are often degraded once they were endocytosed, unlike LDL receptors, resulting in _______ , reducing sensitivity to further stimulation of the ligand
signalling receptors are often degraded once they were endocytosed, unlike LDL receptors, resulting in RECEPTOR DOWN REGULATION , reducing sensitivity to further stimulation of the ligand
signal receptors that are endocytosed and meant to be degraded are often tagged with _____
ubitquitin
following internalization of vesicle bound membranes, materials, and receptors, they are all transported to the ____, which act as redistribution centres of the endocytic pathway
ENDOSOMES
lumen of the endosomes are ______ acidic or basic
acidic
Early endsomes are located ____ and late endosomes are located ____. Late endosomes are also known as :
Early endsomes are located Near the plasma membrane where the vesicle budded and late endosomes are located closer to the nucleus, more into the cell. Late endosomes are also known as : multivesicular bodies. MVBs
LDL receptors and housekeeping receotrs dissociate from their ligands due to the ______pH in the EARLY endosome, and are concentrated into the _____ to be brought back to the plasma membrane.
LDL receptors and housekeeping receotrs dissociate from their ligands due to the ACIDIC pH in the EARLY endosome, and are concentrated into the RECYCLING COMPARTMENTS to be brought back to the plasma membrane.
While the housekeeping receptors go to the recycling compartments, the LDL ligands move to the _____, and ultimately end up in the ____ for digestion.
While the housekeeping receptors go to the recycling compartments, the LDL ligands move to the LATE endosome, and ultimately end up in the Lysosome for digestion.
signalling receptors are not recycled, and get tagged with ____ and transported to the ____ WITH THEIR LIGANDS .
signalling receptors are not recycled, and get tagged with Ubiquitin and transported to the Late endosome WITH THEIR LIGANDS .
how do molecules or vesicles end up in the late endosome following RME?
orchestrated through ESCRT proteins, which sorts through ubiquinated compounds and facilitates the fusing to the late endosomal membrane.
each LDL containes cholesterol that is ____ onto long chains of fatty acids.
esterfied
the core of LDL is surrounded by _____ proteins, which can bind to LDL/housekeeping receptors on cell surfaces for RME.
surrounded by apolipoproteinB-100 protein
LDL receptors and LDL are transported in ____ pits and the LDL receptor is recycled back into the membrane, while LDL ligands are moved to the ___ endosome and later _____
LDL receptors and LDL are transported in COATED pits and the LDL receptor is recycled back into the membrane, while LDL ligands are moved to the LATE endosome and later LYSOSOMES
what happens when there is too much LDL? why is this bad?
- too much LDL gets chemically altered and results in the production of O2 free radicals, which injure blood vessels
- injured blood vessels cause macrophages to ingest the LDL, becoming FOAM CELLS
- foam cells trigger smooth muscle growth and produce dense tissue matrices that bulge into the arterial lumen which cause CLOTS and HEART ATTACKS and PLAQUES
HDLS
high density lipoproteins. carries cholesterol to liver for EXCRETION, opposite of LDLs, which carries cholesterol from the liver to cells around the body for USE. associated with lowering cholesterol levels.
phagocytosis= cellular ____
eating.
phagocytosis= cellular ____
eating.
process of phagocytosis
plasma membrane takes up a particle/microorganism and pinches off to form a phagosome. Phagosome fuses with lysosome and the material is digested. any residual body is exocytosed.
proteins meant for peroxisomes, mitochondria or chloroplasts all are made by
free ribosome
proteins destined for the peroxisome contain the :
peroxisomal targeting sequence (PTS)
T/F: proteins destined for the peroxisome can be imported to the peroxisome already in their folded state
true.
The first tag required for proteins destined for the mito is:
the presequence tag.
T/F: proteins destined for hte mito can be imported to the mito already in their folded state
false. they must be unfolded. chaperones in the mito will refold them back.
T/F: all proteins destined for the mito must enter through TOM complex
true. TOM complex is located on the OMM.
The intermembrane of the mito contain the ____ complex.
TIM
two major TIM complexes
1) TIM22: binds to INTEGRAL matrix membrane proteins. (ex/ succinate dehydrogenase)
2) TIM23: binds to matrix proteins.
movement of proteins into the matrix is ____dependent
voltage.
proteins targeted for the Inner Membrane of the mito contain a _____ sequence
internal membrane/internal targeting/ inner mitochondrial sequence.
proteins targeted for the mito matrix has a _____ sequence
presequence tag ( like other proteins in the OMM)
as proteins enter the matrix ____ (type of chaperone) assist with refolding the protein.
mtHsp70
T/F: ATP hydrolysis is required to pull the protein through the TIM 23 pore into the matrix
true
Biased diffusion
prevents the polypeptide from escaping back into the innermembrane space from the matrix.
complex on outer membrane of chloroplast that allows proteins into the chloroplast
TOC complex
complex on inner membrane of chloroplast that allows proteins into the stroma/thylakoid spaces
TIC complex.
T/F: proteins destined for the chloro can be imported to the chloro already in their folded state
false. proteins must be unfolded prior to entering the chloroplast, and will be refolded by Hsp60,70, or 90 chaperones in the chloroplast itself.
proteins destined for chloroplast containes the _____ sequence
transit peptide sequence
proteins in destined for the stroma have the ___ sequences
1) transit peptide sequence
2) stroma targeting domain
proteins meant for the thylakoid lumen or membrane contains the :
1) transit peptide sequence
2) stroma targeting domain
3) theylakoid lumen transfer domain
Signal sequences of proteins:
1) proteins moving from free ribosomes to membrane bound on RER
2) resident proteins on RER
3) Membrane bound proteins on ER
4) proteins for nucleus
5) proteins for lysosome
6) proteins for peroxisome
7) protins for mito and matrix
8) proteins for inner membrane bound mito
9) proteins for chloroplast stroma
10) proteins for chloroplast thylakoid protein
1) SRP
2) KDEL
3) KKXX
4) NLS
5) mannose-6-phosphate
6) PTS peroxisome target sequence
7) Presequence
8) inner mitochondrial targeting sequence./ inner targeting sequence
9) Transit peptide sequence + stroma targeting domain
10) transit peptide sequence + stroma targeting domain + thylakoid transit domain.
pinocytosis vs endocytosis
pinocytosis: NONSPECIFIC uptake of FLUIDS
endocytosis (RME): SPEICIFIC uptake of SOLUTES/MOLECULES following their binding to receptors on the external surface.
substances that enter the cell through RME become bound to ____ on the plasma membrane that invaginate into the cytoplasm and pinch free of the plasma membrane in ___ coated vesicles
substances that enter the cell through RME become bound to COATED PITS on the plasma membrane that invaginate into the cytoplasm and pinch free of the plasma membrane in CLATHRIN coated vesicles
