week 8 Flashcards
where is the contractile ring
at the metaphase plate
examples of actin and myosin in non-skeletal muscle cells
- cytokinesis, smooth muscle, vesicle transport, cytoplasmic streaming, cell migration
what does the organization of a contractile ring resemble
- sarcomere, just rolled in
wehre to tind sarcomere-like structures
- contractile ring (different because not stable, contraction requires the loss of components)
- adhesion belts (contractile rings formed when you want to compress things)
- ## stress fibers (migrating cells)
difference of actin an dmyosin in non-skeletal muscle cells
- structures are not stable, whereas structure in sarcomere of our muscle is stable.
- things here are constantly being polymerized and depolymerized
how is smooth muscle contraction regulated
- myosin phosphorylation.
- calcium activates a CaM kinase
- kinase activates myosin light chain by phosphorylation, allows for conformational change and contaction
- light chains form a filament resembling a thick filament
- altering conformation of myosin and heavy chain
why can smooth muscle contraction be more persisntent
- ## no T and t, myosin can hold on and bind to actin at same time
is smooth muscle contraction or skeletal muscle contraction faster
- smooth muscle lacks trop and trop
- smooth muscle is more persistent contraction than skeletal muscle
vesicle transport
- formin is localized in the buds, and acts as a plus endnucelating site, actin polymerized at these sites.
(rho gtp also there) - minus end is being pushed away when polyemrizing
- end up with plus end in bud, xo myosin 5 can move in and transport everything
- myosin 5 alwso pulls nucleus into bud by pulling on mictorubule cyctoksletion
how is myosin 5 actiavted
must be activated, only when bound to cargo, can transport many different type sof carho
what organism is used to observe vesicle transport
- budding yeast cell/fisiion also
- formation of a small bud that has a cell wall, must get material in the bud into the daughter cell
what is actin capped by in vesicle transport
formin
what does vesicle transport do
what special interaction takes place in vesicle transport
- positioning of nuclear via Mts
- interaction of actin and microtubules
cytoplasmic streaming functions
- helps in diffusion/gas exchange in plant cells
cytoplasmic streaming process
- cortical actin network track around plant cell transports things
- as things are moved along actin cytoskeleton, causes movement in cytoplasm which makes gas exchange and diffusion more efficient
when is cell migration important
particularly in embryogenesis, and sometimes in adults
when does cell migration happen in adults
- immune response
- in injury, for repairs
- pregnancy
- cancer
focal adhesions
- where cell sticks to substrate
- located on either side of the stress fibres
- actin cytoskeleton linked to transmembrane integral proteins that linkmto EC matrix (links cytoskeleton to eC matrix, so that when cell moves, cytoskeleton contracts
chemotaxis
- there are receptors for the chemoattractant all around cell
- ligand. binds to dreceptor
- triggers cell movement
- actin polymerization in that direction and membrane is pushed forward (involves fillapodia and lomellapodia)
actin in dominant active rho cell
- rho always on which activates forming to make stress fibres
actin in control cell
- fluorescent lining on exterio
actin in dominant active cdc 42
- creates lots of fillapodia
actin in dominant active rac
- ruffling caused by making lots of lamella podia randomly in cel all around
scratch closure assay
- confluent (contact inhibited cells) are scratched, and filled in,
- in inactive forms. of either of the three molecules (arc, cdc 42 or rho), there is no wound closure i.e. no cell migration
what is the order of activation of the three important players in cell mgiration
cdc42, rac, rho
cdc42 functions in cell migration
- activates WASP, then ARP2/3 which causes actin poylermziation and formation of filopodia
- also coordinates actin microtubules and polarity by activating par6
par6
tells us where the rfron of the cell is
- in response to par6, you will have poylermizing icotubles coin
what happens in response to cdc42 activation at the front
- chemoattractant activates receptor, activates cdc42
- wherever cc42 is active is the front
- rac activation leading to arp2/3 acivation = more networking at front
- rho activation leading to myosin 2 activation= polymerize actin budneles with forming and activate myosin so they become stress fibres
- coordinates cell with other city networks (e.g. activates par6 molecule so that everything knows where front of cell is so everything can transport things there)
basic subunit of intermediate filaments
tetramer; the 2 dimers that come together in antiarallele fashion means there is no polarity because teh two sides are teh sme.
characteristics of intermediate cilmanets
- not flobular
- no nucleotide (atp or gtp) needed
- no polaroty
- no known motor proteins
- less dynamic
- involved in cella nd tissue integrity
- assembled onto pre-existing elements
- great tensile strength
- actin and tubulin can be quickly polymerized anddepolymierzine,but not if
Main types of if
- keratins
- design, veimentin
- neurofilaments
- lamins
keratin
- epithelial cells, tissue strength an inteigry
desmin
muscle cells, striated and smooth. provides ontegrity to muscles cells, supports smooth an strained.
- sarcomere organization, integrity
vimentin
- mesenchymal cells (life (migratin cells0
- e.g. rirboblast
- provides integrity to migrant celsll
- sarcoma organization, integrity
neurofilametns
providee structure to axon
- found in neurons
- has that staggered non conitoujs structure
- axon organization
lamina
- found in nucleus
- involved in nuclear structure and organization
- support to ncuelcues
- provide structure to nuclear memernsae
- nucelar structure and organizzato
plectin cross-links wjat
IF vimentin and micotbubles
intermediate filament associated proteins like plectin
- help link IF to other things in membrane (for e.g. other cyto components)
in wha t form must Rac Rho and cdc42 be in for cell migration (these are th Rho proteins)
- proteins must be in gtp form to be active and involved in actin polyermization
stress fibres in cell migration
- associated with cell adhesion are long actin fibres
- interact with myosin and other regulator moecuels
- are contraitle
- bundles of actin
- sarcomere-like organization
- stress fibres contain focal ahdesions
what are the types of cell adhesion
- tight junctions, gap junctions, cell-cell adhesions, cell-eCM adhesions
epithelial cells will be the focus, describe the characteristics
- they form the barrier, skin, intestine lungs
- help regulate what is transported across them
- have polarity because they have an apical and basal surface
apical surface of epithelial cells
outer surface, e..g gut lumen facing the food in our intestine
basal surface
- facing the EC matrix/connectiec tissue in the eC matrix, and basal lamina
that makes up the EC matrix
- the basal lamina, and the connective tissue
basal lamina
- a sheet of proteins
how does adhesion in epithelial cells happen
- desmosomes and IF
- hemidesmosomes that link the cells to the EC matrix
gap junctions
- allow communicaiton and passage via small molecules
- channel regulated by calcium
- allow the passage of ions so epithelial cells usually haec the same concentration of ions which is important for transport across epithelial cells
what are gap junctions composed of
- 6 connexins from a connexon
- each gap junction is essentially 2 connexons, so 12 connexins total
- there are different types of connexin proteins classified by their molecular weight
what happens when there is cell damage
- this leads to high levels of calcium inside the cell cytoplasm
- inner sides of connexins are not usually exposed to calcium
- this causes the gap junctions to close
tight junctions
- membranes form adjacent cells form barrier
- rows of occludin, claudin, and JAM proteins in each cell, apical surfaces of the membranes must be bound together by the three proteins
- we want membranes of cells to be tightly bound to avoid formation of tight junctions
are gap and tight junctions strong
- not really, have important functions but not really involved in strength
cell adhesion
- homophobic interactions an heterophilic interactions
- homophile
homophilic interactions
- cadherins
- IG superfamily
** are on the same molecules, proteins present on once cell are present on antother cell to get the adhesion
terophilic interactions
- integrins
- selectins
- cell-cell or cell-eco
- adhesion between diff molecules
- one is bound to PM and the other is bound to EC matrix?
Ig superfamily
- mediates calcium independent homophilic cell adhesion
- NCAM, ICAM
- some homology to immunglobins not in function
- homophilic
- both cells need NCAM for ex
- transmembrane
cadherins
- over 40 types
- homophilic
- single transmembrane domain
- cytosolic C terminal tail that is associated with cytoskeleton
- transmembrane
- ## EC domain of the protein on one cell interacts with that of another cell
are cadherin binding or ig superfamily calcium depencent
- only chagrin is acA DEPENDENT
- NEED CA TO BIND TO EACH OTHER
types of cadhersns (remember that tu must have two of teh same in order for cells to bind together)
- E cadherin (epidermal tissues)
- N cadherin (nervous tissues)
what happens when cadherins interact with the cytoskeleton inside the cell
- they can create adherent junctions
- when these line up with each other, can form a circumferential belt that can be contractile
how do most cell adhesion structure slink to the cytoskeleton
-n in a way that that allows cell signalling
- cells now if they are linked to each other or not
- adhesions can signal to cell nucleus if things are broken
cytoplasc domain can link to the cytoskeleton
what happens when cell adhesion is broken
- signalling cascades
what structures can form when cadherins link to actin cytoskeleton
- can form contractile circumferential belt or adherens junctins
what structures form when cadherins link to IF such as kertain
- desmosomes
adapter proteins
allow cadherins to link to teh cytoskeleton, for both actin and IF
- will signal to nucleus when cells pull apart for example, signal of adhesions e.g. beta catenin
desmosomes
link the intermediate cytoskeleton with cahderins
what cell surface do contractile rings act on
the apical surface e.g for contraction
what are gap junctions good for in the cell
- communicaiton
ECM proteins examples
- proteoglycans
- collagens
-laminin
-fibronectin
functions of eC matrix
- anchoring and surrounding cells to mtainin cell archietecutre
- control cell functions such as cell polarity, survival proliferation differentitaotn, fate etc
- inhibit or facilitate cell mifraitn
- bind to nd act as a reservoir of growth factors e.g. setting up concentration gradients of the factors, acting as co-receptor for the factors etc
- activation of cell surface signalling receptors
proteoglycans
- hydrophilic, fourd in joints, hydration and residency (e..g lens in eye)
- absorb water
collagens
- structural fuctions
laminin
adhesion, migration
fibronectin
- migration, adhesino
integrins
-heterodimeric transmembrane protein (alpha and beta subunit)
- heterophilic interactions with EC matrix componenta
- have different combinations of alpha and beta subunits
- bind to core RGD amino acids but require nearby synergy regions for specificity
alpha1beta1
collagen
alpha5beta1
fibrongctin
alpha6beta1
laminin
intern interaction with actin
- stress fiber, forms focal adhesion at fibronectin resulting in stress fibre
integrin interaction with iF like keratin
- hemidesmosome formation, non migratory cells,
- keratin with lamina integral protein
inactive integrin
- cannot bind tot he ligand (RGD sequence), cannot bin to EC matrix
when would intern be activated
e.g. in cell migration when needing to form focal adhesion, integral protein would interact with RGD sequence of fribonectin??
how can cell sense when the intern is bound to substrate
- through signalling cascades
selectins
- homophobic adhesion molecule
- binds oligo
- involved in extravastion
