Exam 2 pt2 Flashcards
starts 7.3 slide 4
endolysosome lysosome and late endosome cycle
- late endosome fuse with lysosome to create endolysosome
- endolysosome digest contents to make lysosome
autophagy steps
- nucleation
- extension to form autophagosome
- fusion of autophagosome and lysosome
- digestion
M6P groups are added in
cis golgi
addition of M6P marker
explain process
- lysosomal hydrolase with signal patch binds recogn site of GlcNAc phosphotransferase
- UDP-GlcNAc binds catalytic site
- transfer of GlcNAc to mannose residue on the hydrolase
- release from phosphotransferase
- GlcNAc removed
- hydrolase with a M6P marker
Sorting signal attached to acid hydrolases destined for lysosomes
M6P
M6P receptor proteins are returned to the trans Golgi network via
retromer-coated transport vesicles
after hydrolase is marked with M6P what happens
explain process
- M6P marker is recognized by receptor that binds it
- clathrin coated vesicle buds off
- fusion with early endosome, cargo and receptor in endosome
- hydrolase cargo unbinds due to the pH being acidic
- lysosomal acid phosphotase removes the phosphate so cargo cannot rebind receptor
- receptor taken back in retromer coated vesicle
M6P receptors bind to M6P groups in pH _ in the _
pH 6.5-6.7 in the trans golgi
M6P receptors release M6P groups at pH _ in the _
pH 6, in the endosomes
M6P receptor protein contains…
a sorting signal recognized by the retromer complex
Lysosomal storage disease
Condition in which defects in lysosomal hydrolases cause an accumulation of undigested substances
Inclusion-cell disease (I-cell disease)
A severe type of lysosomal storage disease in which almost all hydrolases are missing from lysosomes, caused by a defect in GlcNAc phosphotransferase
Hurler’s disease
A type of lysosomal storage disease in which a hydrolase responsible for the breakdown of certain glycosaminoglycans is mutated or deleted
Lysosomal exocytosis
Process in which lysosomes fuse with the plasma membrane and secrete their contents into the extracellular space
Melanosomes
Specialized lysosomes that store pigments for eventual release by exocytosis
types of endocytosis
- pinocytosis
- macropinocytosis
- receptor mediated endocytosis
- phagocytosis
Pinocytosis
The continuous ingestion of plasma membrane and extracellular fluid by clathrin-coated or clathrin-independent vesicle formation
Process also known as pinocytosis
cell drinking
Macropinocytosis
Noncontinuous, clathrin-independent endocytosis triggered by the binding of specific ligands to cell-surface receptors
Receptor mediated endocytosis
Process in which specific, receptor-bound cargo is efficiently and rapidly taken into the cell by clathrin-coated vesicles
Phagocytosis
Process by which large molecules, microorganisms and cells are taken in from the cell exterior for delivery to lysosomes
cell eating
phagocytosis
phagocytic cells
Cells which specialize in the uptake of microorganisms, large particles and dead cells from the extracellular environment
_ regulates the protein composition of plasma membranes
recycling endosomes
Most endocytic vesicles fuse with _ , where _
early endosomes, where their cargo is sorted
The recycling pathway operates…
continuously, compensating for the constant loss of plasma membrane due to nonstop endocytosis.
Endosomes _ as they mature into late endosomes
begin to acidify their lumens
Membrane proteins destined for degradation are internalized in _ to form _
intralumenal vescicles to form multicesicular bodies
most cells _ within small pinocytotic vesicles
continuously ingest bits of plasma membrane and EC fluid
non clatherin pinocytosis is done by
caveolae
caveolae
Plasma membrane pinocytic invaginations lacking clathrin coats
some viruses use _ to infect _
use caveolae to infect endosomes, to the ER then the cytosol
macropinocytosis process
- activation of signalling receptor
- plasma membrane protrusion from actin rearrangement
- ruffle (protrusion) collapses
- vacuole closure
- this makes macropinosome (vesicle)
7.4 pg 8
receptor mediated endocytosis is better for _ than pinocytosis
uptake of specific molecules
cholestrol transport is an example of
receptor mediated endocytosis
LDL
Lipoprotein particles used to transport cholesterol in the blood
_ binds LDL to LDLR
apolipoprotein B
when cholestrol is required…
process
- LDLr is made
- LDLR binds to calthrin coated pits
- LDLR and LDL vesicles go to endosome
- LDLR are recycled back
- LDL is broken down
defects in cholestrol uptake leads to
atherosclerotic plaques
3 possible fates of endocytosed receptors
- recycled
- transcytosis (moved)
- receptor down regulation (degraded)
receptor down regulation
def
Pathway used to destroy specific receptor by delivering them to lysosomes, resulting in reduced sensitivity to specific signaling molecules
in transcytosis,
molecules are transported from one cell domain across the cell into another domain
Macropinosomes acidify and fuse with_ , where _
late endosomes or endolysosomes, where cargo is degraded;
When recycling occurs, recycling transport vesicles…
bud from early endosomes and either return directly to the original plasma membrane domain, or make a stop at recycling endosomes
In the process of receptor down-regulation…
ubiquitin-tagged receptors are incorporated into the intralumenal vesicles of multivesicular bodies by the sequential binding of cytosolic ESCRT (Endosome Sorting Complex Required for Transport) complexes
phagocytosis can be carried out by
phagocytes like macrophages and neutrophils
Phagocytosis is triggered when…
when receptor molecules on the surface of phagocytic cells recognize
* antibodies
* complement components
* certain oligosaccharides on the surface of bacteria.
* phosphatidylserine on the surface of cells undergoing apoptosis
after receptor binding in phagocytosis…
Receptor binding induces the phagocyte to extend pseudopods which engulf the particle and fuse at their tips to form a phagosome.
_ shapes pseudopods
Localized actin polymerization
the _ regions of antibodies are recognized by _ receptors on the surface of _
Fc, macrophages and neutrophils
local actin polymerization that shapes pseudopods in phagocytosis is activated by
PI3 Kinase
constitutive secretory pathway
- default pathway
- proteins immediately and continuosly delivered to cell surface
- no signal needed
Exocytosis may be _ or _
constitutive (i.e. continuous) or regulated (i.e. in response to a stimulus)
Proteins destined for the cell exterior will follow the constitutive pathway unless they
- contain retrieval signals for return to the ER
- are resident Golgi proteins
- are tagged for delivery to endosomes/lysosomes
- are involved in the regulated secretory pathway
signals which direct secretory proteins to aggregate are
not well defined and may be diverse
clatherin molecules are not present on _ secretory vescicles
mature, budded off
Secretory vesicles are formed in the _ in response to _
trans Golgi network in response to the aggregation of secretory proteins.
Secretory vesicles are formed in the _ in response to _
trans Golgi network in response to the aggregation of secretory proteins.
Immature secretory vesicles are initially formed by
Golgi membrane loosely wrapping around the protein aggregates
In mature secretory vesicles, the lumenal pH
drops due to the action of V-type ATPases
The high concentration in secretory vesicles enables
rapid release of large quantities of protein
Some secretory proteins are synthesized in the ER as
2 things and which
- inactive precursors (which must subsequently be cleaved for activation)
- as polyproteins (which must be cleaved to release individual peptides).
Polyprotein
Protein containing multiple copies of the same or several different signaling peptides; it must be cleaved to release the individual molecules
synaptic vesicle fusion process
- docking (vesicle approaches)
- priming 1 (vesicle partially assembles SNAP or SNARE)
- priming 2 (complexin binds)
- fusion pore opening (when Ca up, synaptogabin activated and replaces complexin)
- fusion complete
most synaptic vesicles after release
do not go back to the endosome, they are directly recycled as vesicle transporters and refilled immediately
to not add to the membrane
an equal amount of exocytosis and endocytosis needs to occur
examples when regulated exocytosis enlarges membrane
cytokinesis, phagocytosis, plasma membrane repair
Epithelial cells have two distinct membrane domains…
the apical domain (faces internal lumen or outside environment) and basolateral domain (covers the remaining cell surface)
Two processes are used to maintain distinct membrane domains:
(1) Membrane components are randomly delivered to a membrane domain, and then specific components are retained and/or removed from each domain; and
(2) Directed delivery of membrane components to appropriate membrane domain
Mutations in any of the ESCRT proteins will prevent
the incorporation & destruction of receptors, causing them to be returned to the plasma membrane.
The M6P receptor not binding to the clathrin vesicles would result in
the vesicle not being able to bud off the plasma membrane
This would mean that lysosomal hydrolases would fail to reach the endosomes.
If the Sar1 protein is unable to bind to GTP then
it cannot insert itself into the cytoplasmic leaflet of the ER membrane. The binding of Sar1 and GTP recruits COPII adaptor proteins and regulates COPII-coated vesicular transport, so if the binding can’t occur then COPII coated vesicular transport from the ER would likely be reduced.
T or F: Once a secretory vesicle is properly positioned beneath the plasma membrane, it will immediately fuse with the membrane and release its contents to the cell exterior.
false, it will wait for more signal
Adenylyl cyclase
ATP to cAMP
A-kinase anchoring proteins (AKAPs)
Proteins which bind the regulatory subunits of PKA to plasma membranes, nuclear envelope, mitochondrial outer membranes and microtubules
Arrestins
Family of proteins which bind to phosphorylated GPCRs and participate in their desensitization by one of two mechanisms; (1) preventing the receptors from interacting with a G protein, or (2) serving as adaptor proteins to couple the receptors to clathrin-dependent endocytosis machinery
Autocrine signalling
signaling cell same as target cell
CaM-K is activated by and mediates
activated by calmodulin and mediates effects of increased cytosolic Ca2+
calmodulin activates and is activated by
proteins, activated by rise in cytosolic Ca
contact dependent signaling
Signaling process involving the interaction between membrane-bound signal molecules on the surface of one cell and receptor proteins on the surface of another cell
Creb binding protein (CRB) activated by and activates
activated by CREB protein, binds to CRE and increases transcription
_ activates CREB which activates _
PKA activates CREB which activates CBP -> CRE -> transcription
cAMP phosphodiesterase
cAMP -> 5’ AMP
CRE
Short sequences, found in many cAMP-regulated genes, which are bound by the regulatory CREB-CBP complex
guanylyl cylase
GTP -> cGMP
PKA activated by _ and does _
cAMP-activated enzyme which phosphorylates serines and threonines on target proteins
desensitization
A decrease in a cell’s response to a stimulus due to prolonged exposure to the stimulus
Effector protein
Protein which, when activated in an intracellular signaling pathway, implements changes in the cell’s behavior.
effector protein examples
- gene regulator proteins
ion channels
metabolic pathway things
endocrine signalling
hormone
GTPase-activating proteins (GAPs)
Proteins which regulate GTP-binding proteins by increasing the rate of GTP hydrolysis
GEFs
promotes exchange of GTP for GDP, activate GTP binding proteins
inhibitory g protein inhibits
adenylyl cyclase and decreases cAMP
IP3 activated by and activates
relased from PIP2 which cleaved, opens ER Ca channels which increase Ca in cytosol
IP3 - R
open in response to IP3, increase cytosolic Ca
JAK-STAT signaling pathway
Signaling pathway activated by cytokines and some hormones, it provides one of the most direct routes from cell-surface receptors to gene regulation. In this pathway, cytosolic tyrosine kinases (JAKs) phosphorylate gene regulatory proteins (STATs)
Kinase cascade
A signaling pathway in which a protein kinase is activated by phosphorylation, and in turn phosphorylates the next protein kinase in the sequence
MAP kinase signaling module
An intracellular signaling pathway composed of three protein kinases acting in sequence (MAP kinase, MAP kinase kinase, and MAP kinase kinase kinase)
NO synthase
Enzyme which catalyzes the deamination of arginine to produce nitric oxide (NO)
Pleckstrin homology (PH) domains
Protein domain used by intracellular signaling proteins to bind PIP3
Phosphoinositide 3-kinase (PI 3-kinase)
A kinase that phosphorylates inositol phospholipids at the 3 position of the inositol ring
Phosphoinositide phosphatase
Enzyme which dephosphorylate PIP3
_ activates PLC that _
Gq activates PLC which then cleaves PIP2 into IP3 and DAG
Phosphotyrosine-binding (PTB) domains
domains on intracellular signaling proteins which recognize and bind to phosphorylated tyrosines
PKC is activated by
Ca+, DAG and phosphatidylserine
phosphotase
removes phosphate from AA of a protein
Ras
A small, membrane-bound monomeric GTPase often required for the stimulation of cell proliferation or differentiation
REceptor down regulation
Adaptation/desensitization to a stimulus which results from the receptor being endocytosed and destroyed in lysosomes.
REceptor ser/threonine kinase
Enzyme-coupled receptors with a serine/threonine kinase cytosolic domain; ligands for these receptors include members of the transforming growth factor b (TGFb)-
Receptor tyrosine kinase (RTK)
Enzyme-coupled receptors with cytosolic tyrosine kinase domains
Receptor-activated Smads (R-Smads)
Latent gene regulatory proteins that are phosphorylated and activated by receptor serine/threonine kinases in response to TGFb binding
Regulator of G protein signaling (RGS)
Alpha-subunit-specific GTPase-activating proteins (GAPs) which inactivate G proteins by increasing the rate of GTP hydrolysis
Scaffold proteins
Proteins which bind to groups of interacting intracellular signaling molecules and organize them into signaling complexes
SH2 domains
Highly conserved phosphotyrosine-binding domains found on intracellular signaling proteins. Proteins with these domains can bind to activated RTKs and any other intracellular proteins that have transiently phosphorylated tyrosines
SH3 domains
Highly conserved proline-rich binding domains found on intracellular signaling proteins
Transforming growth factor-b (TGFb) superfamily
Structurally related, dimeric, extracellular signal proteins which act as hormones or local mediator to regulate many developmental processes, promote tissue repair and regulate immune responses. These signal molecules act by binding to receptor serine/threonine kinases
Tyrosine phosphatases
Highly specific enzymes which dephosphorylate tyrosine residues, making sure that tyrosine phosphorylation signals are short-lived and the level of tyrosine phosphorylation is low in resting cells
Tyrosine-kinase-associated receptors
Enzyme-coupled receptors (e.g. cytokine receptors) which have no enzymatic activity of their own, but instead associate with cytoplasmic tyrosine kinases (e.g. JAKS) to relay a signal
cell surface receptor signal molecules are
hydrophillic
intracellular receptor signal molecules are
hydrophobic
synaptic signaling is fast or slow
fast
endocrine sig fast or slow
slow
synaptic signalling or endocrine have higher affinity
synaptic
synaptic signalling can use
the same signalling for many targets
endocrine requires _ signal molecues
unique
rapid responses involve
proteins already in target cell
slow responses involve
changes in gene expression or synthesis of new proteins
cell respond to signals in
predtermined ways
signal transduction
extracell signals into intracell
intracellular signaling proteins relay signals by
- generating small intracellular mediators
- activating next signaling in the pathway
kinase
removes a phosphate
GTP -> GDP does what
turn off trimeric g protein
GAP increase
rate of GTP hydrolysis, turning off
signalling complexes are more
efficient bc they are close together
hyperbolic cell response
smooth and graded to concentration of moleculel
sigmoidal response to signal
highest change in response at medium concentrations of signal
bistable system
positive feedback so strong that system stays on even after signal is gone
short delay negative feedback mean
initial response to signal is strong but goes down
long delay in negative feedback means
response will oscillate between high and low
G proteins are attached to and composed of
- cytosolic leaf of plasma membrane
- 3 units: alpha beta and gamma
- alpha unite is a GTPase and binds GTP/GDP
GPCR when bound acts as a
GEF and promote GDP -> GTP
binding of GTP causes
alpha unit confor change, G protein released from GPCR, alpha unit seperate from beta-gamma complex
what inactivates the g protein
RGS, which binds alpha subunite and acts as a GAP, promoting hydrolysis
binding of cAMP to PKA
physical
binding of cAMP to regulatory subunit of complex PKA results in disassociation of the 2 catalytic subunits
gene transcription alter pathway
GPCR → Gs → adynyl cyclase → cAMP cytosol → PKA → CREB protein → CBP → CREB+CBP bind to CRE → transcription
Gq →
whole pathway
Gq → PLC → cleaves PIP2 into DAG and IP3
DAG → PKC
IP3 → gated Ca channels on ER → Ca cytosol → PKC
mechanisms of keeping Ca low in resting cells
- cytosol: Na/Ca exchanger, Ca pump
- ER: Ca pump into
- mitoch: Ca into with pump
