Exam 2 Flashcards
ATPase which provides energy for the retrotranslocation of misfolded proteins from the ER to the cytosol.
AAA-ATPase
Enzyme which ‘activates’ fatty acids by the addition of CoA.
Acetyl-CoA ligase
Enzyme which catalyzes the attachment of Co-A-linked fatty acids to glycerol 3-phosphate
Acyl transferase
BiP
Hsp70-like chaperone protein, located on the lumenal side of the ER membrane, which pulls proteins through the protein translocator via ATP-driven cycles of binding and release. This protein also functions as a chaperone protein which recognizes and binds to incorrectly folded proteins, preventing them from aggregating or leaving the ER.
Calnexin
Membrane-bound ER chaperone protein which binds to the carbohydrate domains of unfolded ER proteins, preventing the proteins from leaving the ER.
Calreticulin
Soluble ER chaperone protein which binds to the carbohydrate domains of unfolded ER proteins, preventing the proteins from leaving the ER.
Chaperone proteins
proteins that bind to others to regulate folding
co-translational translocation
translation and translocation of a protein into the ER happening at once
cytoplasm includes
cytosol and organelles
E3 ubiquitin ligase
Enzyme which attaches polyubiquitin tags to unfolded proteins as they exit a protein translocator and enter the cytosol
* marking the protein for destruction by proteasomes.
ER retention signal
Four amino acid sequence at the C-terminal of a protein which prevents it from being translocation from the ER to other organelles.
ER signal peptidase
Enzyme, closely associated with the ER protein translocator, which cleaves ER signal sequences from translocating proteins.
flippase
specific flipper of plasma membrane, results in asymmetric lipid bilayer
free ribosomes function
in the synthesis of cytosolic proteins
glucosidase cleaves
terminal glucose residues from N-linked oligosaccharides in the ER
ER enzyme which adds a glucose residue to ER proteins that are not properly folded.
Glucosyl transferase
Glycosylphosphatidyl-inositol (GPI) anchor
A glycolipid which can be attached to the C-terminus of a protein in the ER lumen; when transported to the plasma membrane the protein will be displayed on the cell surface.
Mitochondrial Hsp70 function
binds to imported proteins as they emerge from the TIM channel, and helps ‘pull’ the protein into the matrix space using the energy of ATP hydrolysis.
Mitochondrial Hsp70 is part of the
TIM translocator
N-glycanase
Enzyme which removes oligosaccharides chains from ER proteins that have been retrotranslocated into the cytosol.
N-linked oligosaccharides are _ linked to _ residues of _
Oligosaccharides covalently linked to asparagine residues of proteins.
nucleoporins are composed of and orientated
repetitive domains and orientated symmetrically across nuclear envelope
Nuclear basket
Network of fibrils which protrude from nuclear pore proteins into the nucleus and cytosol.
Nuclear export receptors (exportins)
Receptors which bind to nuclear export signals and NPC proteins; they function in the translocation of proteins from the nucleus to the cytosol.
Nuclear export signals direct
translocation of proteins from nucleus to cytosol
Nuclear import receptors (importins) bind to
NLS and NPC proteins
Nuclear import receptors (importins) function in
translocation of proteins from the cytosol to the nucleus
Nuclear localization signals (NLS) directs
proteins from cytosol to the nucleus
Nuclear pore complexes (NPCs)
Arrangement of protein subunits which function to regulate the gated transport of proteins between the cytosol and the nucleus.
Oligosaccharyl transferase
Enzyme that transfers a precursor oligosaccharide from membrane-bound dolichol to certain asparagine residues of proteins imported into the ER.
OXA complex
Mitochondrial inner membrane translocator which mediates the insertion of mitochondrial encoded proteins and nuclear-encoded matrix proteins into the inner membrane.
PERK kinase, ATF6 and IRE1 kinase
Three ER membrane proteins which sense, and are activated by, an accumulation of unfolded proteins
_ carry out the unfolded protein response
PERK kinase, ATF6 and IRE1 kinase
Phosphatidic acid
This phospholipid precursor is formed by the attachment of glycerol 3-phosphate to two membrane fatty acids.
Phospholipid exchange proteins (phospholipid transfer proteins)
Water soluble carrier proteins involved in the transport of lipids from the ER to mitochondria.
Porins
Beta-barrel proteins which form large pores in the outer mitochondrial membrane, making it freely permeable to inorganic ions and metabolites.
Proteasomes
Cytosolic structures where poly-ubiquitylated proteins are degraded.
Enzyme which catalyzes the oxidation of free sulfhydryl groups of cysteines residues to form disulfide bonds.
Protein disulfide isomerase (PDI)
GTPase (molecular switch) which functions in the regulation of nuclear import and export.
Ran GTPase
Ran GTPase-activating protein (Ran-GAP) converts
Ran-GTP to Ran-GDP
Ran Guanine Exchange Factor (Ran-GEF)
Nuclear protein which catalyzes the exchange of GCD for GTP, converting Ran-GDP to Ran-GTP.
Proteins which catalyze the conversion of Ran-GTPase between two states (bound GTP or bound GDP), e.g. Ran-GAP and Ran-GEF.
Ran-specific regulatory proteins
Retrotranslocation (dislocation)
Translocation of misfolded ER proteins back to the cytosol for degradation.
SAM complex
Mitochondrial outer membrane complex which helps outer membrane β-barrel proteins fold correctly.
Sec61 complex
Protein complex which forms the aqueous core of ER protein translocators.
Signal-recognition particle (SRP)
Ribonucleoprotein complex which binds to an ER signal sequence as it emerges from the ribosome, halts further translation, and guides the ribosome to receptors on the ER membrane.
TIM22 complex
Mitochondrial inner membrane protein translocator which mediates the insertion of some proteins into the inner membrane.
TIM23 complex
Mitochondrial inner membrane protein translocator, associated with mitochondrial HSP70, which transports some soluble proteins into the matrix space, and helps insert transmembrane proteins into the inner membrane.
Zellweger syndrome is caused by
defects in the import of proteins to peroxisomes.
The ER, golgi, endosomes and lysosomes have lumens equivalent to
the exterior of the cell
nucleus and cytosol communicate via
nuclear pore complexes
3 families of intracellular compartments
- nucleus and cytosol
- ER, golgi, vesicles, endo&lysosomes
- mitochondria and chloroplasts
if there is a protein with no signal sequence
it will remain in the cytosol after it is made
3 mechanisms of movements between cellular compartments
- Gated transport
- protein translocation
- vesicular transport
gated transport is for movement between
cytosol and nucleus
protein translocation is for movement between
cytosol and mitochondria/chloroplasts, perixomes and ER
vesicular transport is for movement b/w
secretory and endocytic compartments
in vesicular transport, membrane…
orientation is preserved
in vesicular transport, _ components are transferred by
soluble components within the lumen of the vesicles
the _ is continuous with the lumen of the ER
perinuclear space
the inner membrane of the nucleus is for
anchoring sites for chromatin and nuclear lamina
outer membrane of the nuclear envelope is continuous with
with ER
transmembrane ring proteins
span the nuclear envelope and anchor NPCs to the envelop (6.1 pg 15)
scaffold nucleoporins
form layered ring structure (6.1 pg 15)
channel nucleoporins
line the central pore and regulate diffusion (6.1 pg 15)
how do cargo transfer by receptors
transport receptors binding to FG repeat on protein tangles then receptors pull cargo through NPC
how is cargo released in nucleus
- cargo with NLS binds to import receptors
- import receptors pull through cargo thru NPC
- binding of Ran-GTP promote cargo release from receptors
- Ran-GTP-import-receptor complex transported back to cytosol
- GAP make Ran-GTP to Ran-GDP
- import receptor and GDP and Ran separate
Import receptors: Binding of Ran-GTP…
promotes cargo release from import receptors
export receptors: binding of Ran-GTP…
promotes cargo binding
nuclear lamins is important to _ and anchored to
important to shape and stability of nucleus and anchored to NPCs and inner membrane proteins
functions of cytoskeletal folaments
- provide mechanical strength
- cell shape and polarity
- organization
- cellular movement
interactions between subunits of cytoskeletal filaments are _ so that
noncovalent, they are dynamic since these bonds are weaker
at the critical concentration…
rate of subunit addition = rate of subunit loss
in actin filaments and microtubles, subunits are added…
more rapidly to the plus ends than the minus ends
minus end needs more dramatic change in conformation
in actin filaments and microtubles, subunits are added…
more rapidly to the plus ends than the minus ends
minus end needs more dramatic change in conformation
subunits added to the polymer of actin filaments
ATP
subunits added to the polymer of tubulin
GTP
in polymer growth or shrink, nucleotide hydrolysis…
decreases the affinity of a subunit which means increases change of subunit disassociating from end of polymer
ATP/GTP cap will form if
the concentration of subunit higher than critical concentration
rate of subunit addition > rate of hydrolysis
treadmilling occurs when
rate subunit addition = rate of loss
when treadmilling,
polymer will move towards plus end slowly
protofilaments are _ and _
unstable and easily broken
lateral bonds b/w…
protofilaments make is so that growth/shrink is easy but breakage is not easy
_ is the rate limiting step in filament formation
nucleation
steps of filament formation
nucleation, elongation, steady state
nucleation is eliminated by
addition of filament seeds
microtubules functions
- provide tracks for transport
- anchoring for organelles
- mitotic spindle seperation
- clia and flagella
microtubules are formed from
alpha and beta tublin dimers that line up w noncovalent bonds
alpha tublin end
minus end
plus end of microtubules has
beta tubulin
microtubules grow faster at
plus ends
change from growth to shrinkage
catastrophe
_ are seen near plus ends of depolymerizing microtubules
rings of curved oligomers
shrinkage to growth change
rescue
high GTP means microtubules
grow
microtubules depolymerize after losing the GTP cap and if
GTP is below Cc
_ alter microtubules stability
plant toxins
gamma tublin are involved in
microtubule nucleation
microtubules are nucleated at
microtubule-organizing centers (MTOCs)
nucleation of microtubules depends on
gamma tubulin ring complexes which are organized into a ring and prevent loss of subunits at minus end
in most animal cells, MTOCs called _ are
centrosomes are in the nucleus
centrosomes are composed of
a fibrous percentriolar matrix containing gamma TuRC and two perpendicular centrioles
microtubles growing from gamma TuRC have the _ end near
the minus end near centrosomes and the TuRC
centrioles are
- composed of microtubules and accessory proteins
- make poles of spindle apparatus
centrioles structure
centriolar microtubules form nine triplets in a cartwheel shape
cells use accessory proteins to
- regulate microtubule length, stability, number and orientation
MAPs
microtubule associated proteins
* bind to microtubules
the concentration of tubulin monomers is usually
higher than the Cc
stathmin…
decreases concentration of microtubules subunits, favor depolymerization
katanin…
severs microtubules near their MTOC, leading to depolymerization
* might plan a role in mitosis
MAP2 is in _ and has _
dendrites and has a long projecting domain so microtubules are farther apart
Tau is in _ and has _
axons and has a short projecting domain so microtubules are closer together
microtubule motors bind to cargo with _ and bind to microtubules with _
cargo with tail domain
microtubules with motor/head domain
motor/head domains functions
- determine direction of motor
- determine binding
- hydrolysis of ATP
microtubule motors move by
simple
ATP hydrolysis
_ are minus end moving motors
dyneins
_ are plus end moving motors
kinesins
kinesin dimer moving processing
- rear head detaches from tublin binding site by hydrolysis of ATP on back head
- exchange ATP in, ADP out on forward head causes neck of leading head to zipper down
- zippering down throws rear motor domain forward to next binding site
9.3 pg 5
each motor domain of kinesis consists of
catalytic core and neck linker
cytoplasmic dynein functions
- movement of organelles
- construction of mitotic spindle
- infraflagellar transport
axonemal dyneins function
function in the beating of cilia and flagella
cytoplasmic dyneins are composed of
two heavy chains and multiple intermediate and light chains
heavy chains contain
domains for microtubule binding and ATP hydrolysis
intermediate and light chains help to
mediate dynein function
dynein movement steps
- motor domain stalk attaches to microtubule when ATP turn to ADP
- release of ADP results in conform change and the head of motor domain and stalk rotate relative to the tail
- this is called a power stroke
9.3 slide 8
Dynactin
Large protein complex which links cytoplasmic dynein to the membranes of organelles
Anterograde movement
Kinesin-mediate movement of vesicles and organelles towards axon terminals
Retrograde movement
Dynein-mediated movement of vesicles and organelles along an axon towards the nerve cell body
Centripetal movement
Movement of organelles and vesicles towards the cell center
Centrifugal movement
Movement of organelles and vesicles towards the cell periphery
centripetal movement is _ and mediated by _
rapid and smooth and mediated by dynein
centrifugal movement is
a jerky tug of war between kinesin and dynein that kinesin wins
decreasing cAMP levels results in movement of _ to _ via _ since _ is inactivated
decreasing cAMP levels results in movement of granules to cell center via dynein since kinesin is inactivated
cilia beat in a
whip like motion
* fast power stroke is when cilium is fully extended and sweeps forward
* slow recovery stroke cilium curl backwards
like breast stroke
_ form the core of cilia and flagella
axonemes
axoneme consist of
nine doublet microtubules, a central singlet microtubule pair, dynein arms, nexin links and other associated proteins
force generated by dynein causes
axoneme to bend
how do nexin link function in bending of cilia
- w/o nexin, doublets would slide when dynein walk
- nexin link convert dynein energy released from conformational change into bending motion
- they do this with cycle of de/attach b/w motor head and doublet of axoneme
cilia and flagella arise from
basal bodies
proteins from cytosol are carried _ direction toward tip of cilia by _
anterograde, kinesin
primary cilia are
nonmotile bc no dynein arms
primary cillium are made at
centrioles
in mitosis, primary cilia
use centrioles as basal bodies to nucleate
primary cilia are used in nose
and ears to responsd to external enviroment
Human diseases linked to defects in cilia
Ciliopathies
_ is required for all translocation of nuclear encoded proteins
TOM complex
5 mitochndrial protein translocators
Active nuclear import of large molecules and protein complexes depends upon the presence of _ being recognized by _
nuclear localization signals (NLS) being recognized by nuclear import receptors
TOM is on the _ membrane of the mitochondria
outer
TIM complexes help with
insertation of proteins into inner membrane
OXA complex helps with
insertation of proteins into inner membrane
SAM complex helps with
folding of outer membrane beta barrel proteins
steps for protein translocation into matrix of mitochondria
- TOM recognizes SS
- TOM transport across outer membrane with ATP
- TIM23 recognize SS
- TIM23 transport into matrix with electrophoresis
- Hsp70 helps pull protein in
Transport through TOM complex
describe
- cystolic Hsp70 deliver to TOM
- SS recognized
- ATP hydrolysis used to release protein from Hsp70
transport through TIM23
described
- membrane potential used to pull SS through
- release of mitochondrial Hsp70 requires ATP hydrolysis
insertation of porins into outer membrane
describe
- transported into Intermembrane space by TOM
- bind to chaperon to prevent aggregation
- bind to SAM to insert into outer mem and fold
translocation of proteins to inner membrane of mitochondria
describe
- SS through TOM and TIM23
- stop transfer sequences prevents transolcation into matrix
- TOM complex pulls remaining protein into IM space
- protein anchored by stop transfer sequence after SS is cleaved
transportation of multipass transmembrane proteins into inner membrane of mitochondria
- TOM translocates into IM space
- IM space chaperone proteins guide to TIM22
- TIM22 weaves protein that has alternating SS and stop transfer sequences
like sowing machine
function of peroxisomes
- oxidize
- catalasys of H2O2
- beta oxida
- synthesis of plasmalogens
plasmalogens
lipids abundant in myelin sheaths f axons
translocation of proteins into peroxisomes
- peroxins are membrane translocators
- import receptor proteins bind to SS, accompany cargo, release then return to cytosol
zellweger syndrome is caused by
defects in the import of proteins to peroxisomes
2 ways perioxisomes are made
- budding from ER
- fission
the ER is a
branching network of interconnected tubules and flattened sacs that extends throughout the cytosol
SER functions
- synthesis of steroid hormones,
- the detoxification of lipid-soluble drugs
- the storage of Ca2+.
the ER is continuous with
the outer membrane of the nuclear envelope
import of ER proteins is mostly
co-translational
Water-soluble proteins destine for lumens of organelles, or secretion into extracellular space are
completely translocated across the ER membrane into the ER lumen
membrane bound ribosomes function in
co-translational translocation into the ER
free ribosomes function in
synthesis of cytosoic proteins
singal recognition particles (SRPs) are _
rod like ribonucleoprotein complexes with a SS binding site
Proteins are directed to the ER by an _ , which are bound by _ as they emerge from the ribosome exit site
ER signal sequence,
signal- recognition particles (SRPs)
function of translation pause domain of the SRP
gives the SRP-ribosome complex time to bind to the ER membrane
* makes sure protein is not released into cytosol
SRP-ribosome complex translocation into RER membrane
- SRP binds to a SRP receptor on ER membrane
- ribosome is guided to protein translocator on ER membrane
- SRP and SRP receptor are released
- translation restarts and protein crosses ER membrane via translocator
6.3 page 12
how do proteins post translationally translocate into the ER
- accessory proteins are needed
- eukar: BiP cycles of binding and release is driven by ATP hydrolysis which pulls protein into the ER lumen
when there are more positively charged AA right before the start transfer signal, the oreintation of the transmembrane protein is
c-terminus in ER lumen
when there are less positively charged AA right before the start transfer signal, the oreintation of the transmembrane protein is
n-terminus in the ER lumen
tail anchored proteins translocation into ER membrane
describe
- pre targeting complex recognize c terminal
- brings it to Get3 ATPase
- complex interactions with Get1-Get2 receptor complex in ER membrane
- Get3 hydrolyzes ATP
- tail anchor is inserted in membrane
6.3 pg 21
most proteins in ER are glycosylated by
the transfer of a precursor oligosaccharide from a dolichol membrane lipid
N-linked glycosylation is catalyzed by
oligosaccharyl transferase
The first sugar of _ is added in the ER, and the remaining residues are added in _
O-linked oligosaccharides, remaining in GOlgi
calnexin and calreticulin function
binding to unfolded proteins so they cannot leave the ER
cycle of making sure protein is properly folded
- calnexin/calreticulin binds unfolded protein
- glucosidase removes final glucose and free protein from calnexin/calreticulin
- glucosyl transferase determine if protein folded right
- if not, add new glucose and repeat cycle
_ determines if protein folded right
glucosyl transferase
3 sensor for misfoded poteins
- IRE1
- PERK
- ATF6
PERK pathway
PERK activates
* phosphorylates/inactivates and translation initiation factor
* increased levels of a transcription regulator for UPR response
ATF6 pathway
ATF6 cytosol domain cleaves and regulates transcription of UPR genes
IRE1 pathway
- misfolded protein bind to IRE1
- ribonuclease domain activated
- pre-mRNA made into mRNA by take out intron
- translation of mRNA
- makes a transcription regulator
- upregulation of transcription of chaperon mRNA
how lipid bilayers are assembles in the ER
- fatty acid delivered by FA binding proteins
- acyl transferases at 2 FA to glycerol
- layer bigger
_ cannot be removed from the membrane
in lipid bilayer formation
phosphatidic acid
Why are the GPI-anchored proteins of the plasma membrane always located in the extracellular space?
These proteins are always located in the extracellular space because enzymes in the ER covalently attach the GPI anchors to certain proteins in the plasma membrane. The linkage of these proteins and anchors occurs in the lumen of the ER which is equivalent to the extracellular space. Therefore, they are always located in the extracellular space.
The _ is a meshwork of interconnected intermediate filament proteins that gives shape and stability to the nuclear envelope.
nuclear lamina
Directionality of transport in the _ is regulated by Ran GTPase.
nucleus
Acid hydrolases
Type of hydrolytic enzymes found in lysosomes which require a low pH environment for activity
Lumens of membrane-enclosed compartments involved in _ and _ pathway are topologically equivalent to the _
biosynthetic- secretory pathway and endocytic pathway are topologically equivalent to the cell exterior
Proteins can travel through the spaces of the organelles in these pathways without having to cross membranes
biosynthetic- secretory pathway and endocytic pathway
Biosynthetic-secretory pathway
- travels outward
- ER → Golgi → cell surface or lysosomes
Endocytic pathway
- travels inwards
- Plasma membrane → endosome → lysosome
Retrival pathway
brings proteins back to original compartment
THe _ balances the flow of membrane b/w compartments
retrieval pathway
Functions of protein coats
- Inner layer of coat selects and concentrates specific membrane proteins into a membrane patch
- Outer layer of coat molds the forming vesicle
Clathrin-coated transports
from plasma membrane to endosomal and golgi compartments
COP1 coated bud from
Golgi
COP2 coated vescicles bud from
ER
Subunit of clathrin
triskelion
Process of clathrin coated vesicle budding
- adaptor protein binds to **cargo receptor **
- cargo receptor binds cargo
- adaptor protein binds clathrin
- this causes bending of membrane
- dynamin forms a ring around the neck of the bud
- fusion of membrane
- budding off
- vesicle rapidly loses protein coat bc of HSP70
PIPs are made by
PIs undergo rapid cycles of phosphorylation and dephosphorylation of their inositol sugar
what regulates the binding domains of vesicular transport
specific PIP binding
The distinct _ will determine which adaptor proteins will bind, and thus which cargo will be transported
distribution of PIPs within a membrane
The distinct distribution of PIPs within a membrane will determine…
which adaptor proteins will bind, and thus which cargo will be transported
COP2 vesicle formation process
- Sar1-GDP turns into Sar1-GTP
- this exposes the amphiphilic helix on Sar1
- this helix binds to ER membrane
- membrane bound Sar1-GTP binds to Sec24 and Sec23
- membrane starts to deform
- Sec24 binds to cargo receptors
- Sec13 and Sec31 form outer coat of shell
- budding off
outer coact of COP2 shell
Sec13 and Sec31
_ direct vesicles to correct target membrane
Rab proteins and Rab effectors
Largest subfamily of monomeric GTPases
Rab proteins and Rab effectors
how does Rab protein create specialized membrane domains
- Rab5-GDP encounters Rab-GEF and makes Rab-GTP
- Rab5-GTP anchores in endosomal membrane
- Rab5-GTP activates PI3-kinase
- PI to PI3P
- PI3P recruits Rab effectors
how Rab alters membrane identity
- Activation of RabA-GEF
- RabA recruits RabB-GEF
- RabB-GEF recruit RabB
- RabB recruit RabA-GAP
- RabA-GAP inactivates RabA
- RabB replaces by RabB
_ mediate the fusion of the lipid bilayers
SNARE proteins
When v- and t-SNAREs interact…
helical domains wrap around each other and form stable trans-SNARE complexes which lock the two membranes together
what makes sure vescicle docking is highly specific
SNARE complexes
how does vesicle fusion
- water is expelled as two membranes pulled together by SNARES
- lipids form stalk
- lipids make fusion
NSF ATP hydrolysis provides the energy to…
separate the SNARE complex
COPII-coated transport vesicles bud off from _ , moving membrane and cargo to the _
ER exit sites, to the Golgi apparatus
selective transport from the ER: membrane proteins display _ on their _ which are recognized by _
selective transport from the ER: membrane proteins display exit signals on their cytosolic tails which are recognized by adaptor proteins of the inner COPII coat;
selective transport from the ER: soluble cargo proteins display _ recognized by…
exit signals, non-cytosolic domains of the cargo receptors
Non-selective transport from ER is slower or faster than selective?
slower
Non-selective transport from ER
- ER resident proteins (lacking exit signals) may randomly enter transport vesicles, slowly leaking out of the ER to the Golgi.
secretory proteins will be…
packaged in vesicles without the help of exit signals or cargo receptors
Vesicles leaving the ER…
lose their protein coats, fuse with one another (homotypic fusion) via the interaction of SNAREs, and form vesicular tubular clusters.
COPI-coated transport vesicles immediately _ and transport _
begin to bud off vesicular tubular clusters and transport ‘escaped’ resident proteins and cargo receptors back to the ER.
retrieval (retrograde) transport identifies
resident ER membrane and soluble proteins which display retrieval signals.
The structural integrity of the Golgi is contingent on
matrix proteins called golgins
cis face
vescicles arrive from ER, return to ER or go in golgi
trans face golgi
vescicles leave golgi network
cis Golgi network (CGN)
a collection of fused vesicular tubular clusters arriving from the ER.
Transport through the Golgi may occur by one of two mechanisms:
vesicular transport model (cisternae remain static) or cisternal maturation model (cisternae move)
golgi processing has _ and _ organization which means
- spatial: each cisternae contain specific processing enzymes
- biochemical: enzymes can only act on product of previous enzyme
High-mannose oligosaccharides
Oligosaccharides displaying a variable number of terminal mannose residues, all originating from the precursor oligosaccharide added in the ER
O-linked oligosaccharides
Oligosaccharides containing a variable number of sugar residues linked to serine or threonine residues in the Golgi apparatus
mucins
Proteins heavily glycosylated via O-linked sugars, they bind water in the lumens of organs to produce mucus
goblet cells
Cells which secrete large amounts of mucin proteins into the lumens of the GI and respiratory tracts
Vesicular transport model
Model of transport through the Golgi apparatus in which vesicles transport proteins between static cisternae
Cisternal maturation model
Model of transport through the Golgi apparatus in which cisternae form continuously at the cis face, then migrate through the stack as they mature
The lumens of lysosomes are filled with
acidic hydrolases
acidic hydrolases require
acidic enviroments
pH 4.5 to 5
_ in the lysosomal membrane uses energy of ATP hydrolysis to _ for pH of 4.5-5
vacuolar H+ ATPase, pump H+ ions into the lumen
vacuolar H+ ATPase in the lysosomal membrane uses energy of
to do what
ATP hydrolysis to pump H+ ions into the lumen, maintaining a lumenal of pH of 4.5-5.0 (optimal for the activity of acidic hydrolases)
Lysosomal hydrolases and membrane proteins are synthesized in the _ , pass through the _ and are delivered to _
ER, Golgi apparatus, endosomes
Late endosomes contain…
- material via endocytosis
- hydrolases from golgi
