Cell Interactions 1: The ECM Flashcards
what do multicell organisms make contact with? (2)
other cells or ECM
basal lamina
fibroblast & epithelial cells together make the basal lamina or basement membrane
compressed ECM, resilient to epithelial cells
what tissue is almost entirely composed fo ECM material?
connective tissue
what function does the ECM serve when it is a thin layer?
holds cells close together
what function does the ECM serve when it is a thick layer?
cushions or protects
how many specialized cell types do vertebrates have?
100+
what type of ECM do plants, fungi & bacteria have?
a tough ECM, called ‘walls’
what is the role of the ECM in anthropods? & what is the main component?
chitin is the main component
forms exoskeleton
what are the most abundant polymers on earth?
chitin
cellulose
what is the ECM composed of ?
primarily water
PROs
carbs
what are the main macromolecules in the ECMs of animals?
Glycosaminoglycan (GAGs): polysaccharide with an amino grp
PROs –> collagen, elastin, fibronectin & laminin
Proteoglycans: PROs with GAGs covalently bonded
where does the ECM come from?
cells secrete it & secrete surplus for other cells
what type of ECM do fibroblasts have?
connective tissue ECM
what type of ECM do osteoblast cells have?
bone-forming ECM (calcified ECM)
what type of ECM do chondroblast cells have?
cartilage forming ECM
when is the ECM calcified?
bones & teeth
cell wall of bacteria
shells of molluscs
ECM function
Mechanical support
Biochemical barrier
Water soluble materials pass, lipid soluble materials cannot pass & macromolecules move slowly
A medium for:
Extracellular communication with CAMs
Positioning of cells in tissues through adhesions
Repositioning of cells in migration during cell development or wound repair (cells push along ECM)
Tensile strength for tendons
Compressive strength for cartilage
Hydraulic protection
Elasticity in the walls of blood vessels
Calcified for: bones/teeth, cell wall of bacteria & shells of molluscs
Chitinized to form the exoskeleton
why are glycocalyx interactions not considered glycoPROs?
not covalently linked
glycocalyx
carbs attached to the PM PROs & lipids
what is the function of the glycocalyx?
Cell-cell interactions (carbs)
Cell substrate interactions (receptors) Mechanical protection Binding regulatory factors
where is the basal lamina found?
epithelial layers & connective tissues
around muscle & fat cells
under epithelial tissues
Under endothelial lining of blood vessels
functions of the basal lamina (basement membrane)
mechanical support for attached cells (prevents bursting)
generating signals
separating adjacent tissues
acting as a barrier to some macromolecules
establishes polarity (organelles orientate properly)
glycosaminoglycans
unbranched polymers of repeated modified disaccharides
Amino & sulfate grps are added --> negative charge
what is the role of the amino or sulfate grps on glycosaminoglycans?
Attract ions (Na+) which attracts water causing the molecule to puff up into a gel
Account of 10% of the ECM, but puffing up enables them to take up 90% of the ECM volume which provides the compressive strength
what effect does the proteoglycan bound to GAG have?
increasing volume & water drawing capacity
Proteoglycan
PRO backbone covered with an extensive network of carbs
GAGs attach to the backbone
Sulfate grp still draws water in, creating a gel & provides cushioning
what molecules attract water to provide cushioning?
GAGs & proteoglycans
what part of the GAG & proteoglycan structure is sulfated?
carb
where are proteoglycans the most abundant?
in cartilage
Describe the ECM of bone
rich in collagen & proteoglycans bu hardened with calcium phosphate
collagen represents what percent of PRO in humans
25%
what is the most abundant material of the ECM?
collagen
what cell produces collagen?
fibroblasts
how many diff types of collagen are there?
20
collagen
fibrous PRO constituent of skin, cartilage, bone & other connective tissue
function of collagen
Scaffolding PRO, cells have receptors that attach to it
Controls cell shape & differentiation
Remodeled to help broken bones regenerate, wounds heal & directs blood vessels to grow in healing areas
Fibrils shorten & lengthen to create tracks that cells can move on to go where they need to
what does hydroxylating proline & lysine do?
enables electrostatic interactions
structure of collagen
Trimer PRO, made of 3 alpha chains that intertwine to form a triple helix
Proline & lysine get hydroxylated
Fibrils come together for increased strength
Crosslinked at hydroxylated residues
what is required for hydroxylating proline & lysine in collagen?
vit C
scurvy
occurs when diet is deficient in vit C vit C is required for hydroxylating for collagen fibrils to crosslink. Capillaries aren’t held in place & bleed out resulting in bruising
what are the probs that arise from collagen?
Scurvy – occurs when diet is deficient in vit C vit C is required for hydroxylating for collagen fibrils to crosslink. Capillaries aren’t held in place & bleed out resulting in bruising
Increase cross-linking = decreased elasticity occurs with age –> wrinkles
Mutation in type I collagen results in osteogenesis imperfecta – too much crosslinking results in thin, fragile bones which are brittle & break easily
Mutations in other collagen genes results in hyper-flexible joints & extensible skin b/w there isn’t enough hydroxylation
how does collagen differ in tissues?
type of collagen & the arrangement of collagen
how is collagen arranged in tendons?
parallel, in line with the direction of the tensions exerted
how is collagen arranged in the eye’s cornea?
perpendicular to other layers, gives strength while allowing light to pass
fibronectin
multifunctional PRO in ECM
Link cells to ECM
fibronectin structure
Dimer - 2 arms with diff domains that can bind to components of the ECM & receptors
what is fibronectin’s role in embryogenesis?
guides movement of cells
works with collagen
neural crest cells move out to form the nervous sys - follow tracks of fibronectin that other cells have laid out as a guide
primordial germ cells migrate to site of gonads
what does integrin require to bind to the actin network?
adaptor PROs
integrin
integral membrane PRO
integrin structure
heterodimer, 2 polypeptides (alpha & beta chains)
Cytosolic domains: bind to adaptor PROs that link integrins to elements of the cytoskeleton (ex: actin network) Extracellular domains: bind ligands in the ECM (ex: fibronectin, collagen etc.)
when do we see anchorage dependence of a cell lost?
cancerous cells
what is the function of integrins?
When integrins bind to ECM ligands, the structure of the cytoplasmic domain changes causing a signal cascade indicating to the cell to anchor
Anchorage dependence is required for survival in vertebrates, lost in cancer cells Cells use this signal to regulate normal activities (cancer cells divide without this signal)
focal adhesion
how a cell attaches to ECM PROs
Region of PM where there is a focal adhesion is rich in integrins Integrins anchor to actin microfilaments (with adaptor PROs) When adaptor PROs bind to integrin FAK is activated FAK signals to the cell to change shape, move or change in cell cycle
