Cell Bio - Cell adhesion and signalling Flashcards
difference between planktonic and sessile bacteria
planktonic - freely existing in bulk solution
sessile - attached to a surface or within a biofilm
what does the extracellular matrix (ECM) consist of
network of proteins and polysaccharide chains that are manufactured by cells, secreted and modified outside the cell by several different enzymes.
what are the functions of the ECM
mechanical - tensile and compressive strength and elasticity
protection - buffering against extracellular changes and water retention
organisation - control of cell behaviour by binding of growth factors and interactions with cell surfaces
what secretes the matrix macromolecules
fibroblasts
what forms bones and cartilage
bones - osteoblasts
cartilage - chondroblasts
what are the main macromolecular components of the ECM
glycosaminoglycans
fibrous protein
non-collagen glycoprotein
structure of glycosaminoglycans (GAG)
GAGs are unbranched polymers of repeated disaccharide derivatives, including amino sugars, sulfated acetylamino sugars and uronic acids
what are the properties of GAG’s
Acidic and negatively charged
Attract positive ions (eg Na+) which attracts water causing gel formation
Comprise 10% of ECM mass but 90% of volume
GAGs (especially hyaluronan) provide compressive strength
Metabolically cheap bulking agent
what is hyaluronan
GAG
107kDa
spun out of the cell membrane
function of hyaluronan
used to hold together open spaces in the ECM that would otherwise be filled up with cells
structure of a proteoglycan
serine-rich protein decorated with hundreds of O-linked acidic or sulfated GAG’s
what is aggrecan
common proteoglycan in the ECM
Its core protein is decorated with around 100 chondroitin and 30 keratan chains.
what does aggrecan bind to
hyaluronan via adaptor proteins
what is the function of the primary cell wall in plants
flexibility allowing expansion and remodelling
composition of the primary cell wall
cellulose
hemicellulose
pectin
function of the secondary cell wall
rigid providing strength
composition of secondary cell wall
cellulose
hemicellulose
lignin
what accounts for 20% of primary cell wall dry weight
xyloglucan
what is the backbone of xyloglucan composed of
1,4-linked β-D-Glcp residues
what occurs to 1,4-linked β-D-Glcp residues
are substituted at O6 with mono-, di-, or triglycosyl side chains.
where does galacturonic acid occur (Gala)
homogalacturonan (HG)
rhamnogalacturonan (RG)
function of pectin demethylase
demethylates pectin
makes it available for crosslinking via Ca2+ bridges
what is an occluding junction
seals cells together forming an impermeable barrier
anchoring junctions
attaches cells to other cells or the ECM
communicating junctions
allows exchange of chemical/electrical information between cells
function of adheren junctions
important role in determining shape of multicellular structures
forms an indirect link between actin cytoskeletons
what do adhesion belts allow
reshaping of epithelial cells
form vesicles
function of desmosome junctions
indirectly link intermediate cytoskeletons
provides mechanical strength
what are channel-forming junctions
creates a link between the cytoplasm of two cells
what are plasmadesmata
plant equivalent to gap-junctions
structure of gap junctions
each channel is comprised of individual connexin subunits
can be homomeric or heteromeric
assemble into homotypic or heterotypic channels
where are new connexons added
periphery via exocytosis
what does a mutation in connexin 26 lead to
– mutation leads to death of cells in the organ of Corti (electrically active sensory epithelium) Congential deafness
what can mutations in connexins lead to
cateracts and demyelinating disease in peripheral nerves
what is a signal-relaying junction
basically a synapse
difference between cadherins and integrins
cadherins - mediate cell-cell attachment
integrins - mediate cell-matrix attachments
what proteins constitute tight junctions (TJ)
claudin
junctional adhesion molecules (JAM’s)
occludin
ZO
what is claudin
a four-pass transmembrane protein that constitutes TJ strands
what are junctional adhesion molecules (JAM’s)
class of cell–cell adhesion molecules with two Ig repeats that localize to TJs.
what are occludins
four-pass transmembrane protein localized at TJs.
what are ZO proteins
(zonula-occluding) family proteins: TJ- undercoating scaffolding proteins
where are cadherins found and not found
in all animals and choanoflagellates
not present in plants, fungi, archaea or bacteria
name a non-classical cadherin and its function
desmocollin
forms desmosome structures
why is Ca2+ important for cadherin function
binds to the hinge regions of cadherin, prevents flexing
removal of Ca2+ reduces binding affinity at N-terminal
destabilisation leads to proteolytic degradation
function of catenins
form a link between the intracellular cadherin domain and the actin filament
what is the dual role of β-catenin
Intracellular anchor protein at adherens junctions
Transcriptional regulator in Wnt signalling
function of vascular endothelial cadherin (VEC)
required for endothelial survival
required for response to vascular endothelial growth factor (VEGF)
VEGF binds to a receptor tyrosine kinase that requires VE cadherin as a cofactor
structure of integrins
Comprised of 2 non-covalently associated glycoprotein subunits
Short intracellular C-terminal
- Large extracellular N-terminal domain
difference in roles of the extracellular domain and the intracellular domain of integrin
extracellular - binds extracellular matrix proteins or cell
surface ligands of other cells
intracellular - links (usually via Talin) to the actin cytoskeleton
what does allosteric regulation allow for
switching between active and inactive state
describe outside-in activation of integrins
Binding of an extracellular ligand to an integrin results in binding to the cytoskeleton
Transmission of a force via the cytoskeleton
describe inside-out activation of integrins
Intracellular regulatory molecules such as phosphoinositide (PIP2) activate Talin
Causes strong binding of Talin to β integrin chain
In turn this activates the extracellular domain of integrin to bind extracellular ligands
PIP2 can be produced in response to extracellular signals.
Complex crosstalk between different signalling processes
what is heterophilic binding
binding to a different type of molecule
what is a lectin and their function and an example
cell surface carbohydrate binding protein
Mediate transient cell-cell adhesion in the bloodstream
Control binding of white blood cells to the endothelial cells lining the blood vessels
what are the 3 different types of selectins and where are they present
L-selectin - on white blood cells
P-selectin - on platelets and endothelial cells activated by an inflammatory response
E-selectin - on activated endothelial cells
what causes lymphocytes to bind and become trapped
In lymph organs endothelial cells express oligosaccharides recognised by L-selectin on lymphocytes
structure of intracellular adhesion molecules (ICAM)
ICAMs have an extracellular domain characteristic of antibodies
difference between ICAM/VCAM and NCAM in terms of binding
ICAM/VCAM - heterophilic binding to integrins
NCAM - homophilic binding
what charge do neural cell adhesion molecules (NCAM) have and why
negative
high concentration of sialic acid chains
what are the difference between cadherin and NCAM mutations
cadherins - lethal
NCAM - more subtle effects
how does fascicilin3 function
functions in recognition of the tissue by neuronal growth cones
what does fascicilin3 form
homophilic adhesions
what holds the pre/post-synaptic membranes together
cadherins
Ig superfamily
neuroligins
neurexins
where does plant cell adhesion occur
middle lamella - pectin rich domain
what are the different domains of pectin
HGA - homogalacturonan
RGII - rhamnogalacturonan I
RGI - rhamnogalacturonan I
XGA - xylogalacturonan
what can cause loss of plant cell adhesion
Defects in synthesis of plant cell wall polysaccharides
what are the advantages of single cell organisms for models
Fastgrowth in chemically defined media
Relatively cheap culture media
Several molecular tools for manipulation
Extensive knowledge of its genetics and genomics
Extensive knowledge on its transcriptome, proteome, and metabolome
Several strains are considered biosafety level 1 (K12)
what are the disadvantages of using single celled organisms for models
doesn’t have a nucleus/chromatin, not all protein modification mechanisms e.g. glycosylation
features of yeast as model organisms
Rapid growth (1.5 or 2.5 hours)
Non-pathogenic
Efficient transformation by exogenous DNA
Efficient homologous recombination
Simple genetic screens
what are the advantages of organoids over 2D cultures
more physiologically relevant than monolayer culture models.
far more amenable to manipulation of niche components, signalling pathways and genome editing compared to in vivo models.
