Plasma membrane and signaling Flashcards
what are some extracellular signals the plasma membrane responds to? what do extracellular signal need?
-plasma membrane respond to many extracellular signals
–> growth factors and anti growth factors
–> signals that change cell activity (hormones, neurotransmitters)
extracellular signals need a receptor expressed to respond to the signal (hormone)
what 3 domains do most receptors have?
- hydrophobic domains: that extend through the lipid bilayer (i.e. alpha helix)
- extracellular domain: that binds the the message (i.e. hormones)
- intracellular domain: that amplifies signal
what do most signals involve?
most signals involve binding of chemical (signal) to a high-affinity protein receptor on the cell membrane –> a signal that’s propagated into the cytosol
water soluble hormone signalling pathway
- water soluble hormones are membrane insoluble. they bind to membrane receptors
- the binding activates G protein
- the activated G protein activates adenylyl cyclase
- adenylyl cyclase catalyses the conversion of ATP to cAMP, the secondary messenger in this pathway
- cAMP activates protein kinases
- protein kinases phosphorylate proteins in the cytoplasm. this activated these proteins, allowing them to alter cell activity.
what do membrane proteins do?
link cell membrane to cytoskeleton or to extracellular structure (ECM, other cells) and junctions
cell-cell junctions vs. cell-matrix junctions
cell-cell junctions: (from most apical to basal)
tight junctions
adherens junctions
desmosomes
gap junctions
cell-matrix junctions:
hemidesmosomes
actin-linked cell matrix junctions
cytoskeleton
microtubules
microfilaments
intermediate filaments
extracellular structures
tight junctions
desmosomes
hemidesmosomes
adherens junctions
tight junctions
-seperate apical from basal
-selective and “leak proof” or less selection
-regulates movement across membranes and other epithelial cells
anchoring junction- desmosomes
-intracellular component: plaque formed of molecules that are associated with cadherins
–> intermediate filaments (cytoskeleton) bind plaques
-extracellular component: cadherins on 1 cell interact with cadherins on neighbouring cells
-structural integrity for a wide range of cells and tissues
anchoring junction- hemidesmosomes
-similar to desmosomes, but extracellular components involves integrin proteins
–> plaque still binds to intermediate filaments
-the integrin commonly binds the basement membrane/ basolateral
-how epithelial cells stay anchored to basements membrane and underlying connective tissue
what protein and cytoskeleton component are part of desmosomes?
cadherins and intermediate filament
what protein and cytoskeleton component are part of hemidesmosomes?
intern and intermediate filament
anchoring junction- adherens junction
-have plaque to connect to:
–> another cell: cadherins
–>basement membrane: integrins
-connect with microfilaments formed from actin (cytoskeleton)
what protein and cytoskeleton component are part of adherens junctions?
cadherins (connect to other cell)
integrins (connect to basement membrane)
-microfilaments
functions of the cytoskeleton
-cellular movement: move through space (i.e. fibroblast) or perform work and change shape (i.e. muscle cell)
-organize cell components/organelles: mitosis, meiosis, shuttle organelles and residues
-cell structure: strength (skin), shape (absorptive surfaces)
-communication: intracellular signals to regulate growth
microtubules function and molecule
-traffic organelles and cell division
-organization of overall cell structure
-cell movement
–>tubulin
microfilaments function and molecule
-cell movement
-structural organization of plasma membrane
–> actin
intermediate filaments function and molecules
-overall structural integrity of the cell
–> keratins and desmin
3 characteristics of cytoskeleton
- dynamic: filament subunits (monomers, heterodimers) build themselves into polymer strands –> once monomers reach critical [ ] and interact with nucleating factors –> polymer forms
- tightly regulated: filament assembly and disassembly –> intracellular signals
-govern structure and formation of polymers - generate force: proteins interact with strands of cytoskeleton;
-move cell or organelles along the axis of the strands
-generate power or motion in cells through contraction
microfilaments- actin
-monomer: G actin
-polymer: F actin
-nucleating factors stimulate formation of F-actin:
–> formin: linear arrangements
–> ARP 2/3 complex: mesh like nets
-when F-actin is formed, it spontaneously degrades
-each G-actin has ATP bound
-over time G-actin hydrolyzes ATP to ADP, which makes it more likely that it will “fall off” the F actin strand
-F-actin stability depends on a number of factors:
–>[ ] of G-actin
–>”caps” that can be applied to F-actin that prevent disassembly (tropomodulin- capping protein)
–>proteins that increase or decrease rate G-actin hydrolyzes ATP
–>nucleating factors or inhibitory factors that modify the formation of F-actin (i.e. formin, ARP2/3)
-mucsle cell: stable, parallel actin fibres, generate force, strong anchor
-fibroblast: “crawl” to deposit collagen/ ECM; meshes, fibres, filopodium
-use myosin as motor
microtubules
-protein monomer= tubulin
-alpha and beta= form dimers
-alpha beta dimers organize into helical tube
-positive end= alpha
-negative end = beta
–> polarity
-beta monomers hydrolyze a nucleotide triphosphate –> cleave GTP to GDP and Pi
-after GTP cleaved, dimer “falls off” microtubule= dynamic instabilty
-microtubule organizing centre (MTOC):
-made of 2 centrioles that form the centrosomes
-centrioles made of microtubules –> tubulin triplet (9x3)
-microtubules radiate off MTOC –> cellular scaffoling
-put cell structures at specific spots
-determine cell polarity (i.e. lumen vs basement membrane)
-cellular movement: rotate and move in whip like fashion
–> cilia: sperm cells
–> flagella: respiratory mucosa
-cell divide; MTOC splits and pulls chromosomes to new daughter cells
-singalling: the primary cilium; senses important stimuli in extracellular environment to help with cell localization or function
-use kinesins and dynes and motors
microfilaments, microtubules and cellular motors (which proteins do they use)
what do molecule motors use for energy?
-f-actin and microtubules form a network of dynamic filaments that “molecular motors” can move along (i.e. train tracks)
-f-actin: myosin protein- “walk” along microfilaments= cell contract
-microtubules: dynein and kinesin proteins walk along microtubules and cause “whipping” of cilia and flagella
-dyneiens and kinesins move in opposite directions along microtubules
–> molecular motors use ATP to move
intermediate filaments
-stability
-long proteins with alpha helix confirmation that coils round other monomers to form dimers coil (“coiled-coil”)
-more stable than actin and tubulin –> dont hydrolyze GTAP or ATP so dont dissociate easily
i.e. lamina, keratins, vimetins (desmin), neurofilaments
alpha helical monomer –> coiled-coil dimer –> staggered tetramer of 2 coiled-coil dimers –> lateral association of 8 tetramers
