Cell adhesion 2

what are the two things that help cells attach to the ECM

fibronecin and the integrin dimer

what type of dimer do integrins function as

heterodimers

what do integrin dimers do

they transmit function across the plasma membrane and are anchored to the cytoskeleton

what is fibronectin

a molecular bridge between integrins and the ECM

what binding sites does fibronectin have

a binding site for the ECM and a binding site for cells

what are the two subunits of integrin

alpha and beta

where does integrin sit

inside the cell membrane

how can integrin change from inactive to an active form

through a conformational change

how is the conformational change of integrins regulated

by signals from both inside and outside the cell

what does integrin binding to the cytoskeleton cause

a rapid change to the extracellular parts

what does the activation and inactivation of integrin allow

cells to move through tissue

what is a simple explanation of how integrins coordinate cell movement

binding is formed at the front while binding at the back is broken, allowing the cell to move

what is GFP (green fluorescent protein)

used as a reporter to visualise gene expression, protein localisation, and live cell dynamics, often fused genetically to another protein to track it inside living cells or organisms

what is WT1 (Wilms Tumour 1)

in imaging, usually an antibody against WT1 used as an immunostaining marker, it is used for kidney development, mesothelial cells and certain cancers, it is detected by immunofluorescence or immunohistochemistry

can WT1 be used on live cells

no, it can only be used on dead cells

what is DAPI

a chemical dye, a fluorescent DNA stain that binds strongly to A-T-rich regions in the minor groove of DNA and emits blue fluorescence, it is used for nuclear staining and is a common reference marker

is DAPI used in live cells

not usually, but it can be used to stain live cells with compromised membranes

what are GAGs (glycosaminoglycans)

repeating disaccharides, they are negatively charged so they keep a high cation in ECM, draw in water, and create swelling pressure, chains of GAGs are linked to a core protein to form proteoglycans

what is tension in collagen fibres balanced by

GAG swelling pressure

what is the ECM composition of dense connective tissues such as tendon and bone

they have less GAG and more collagen, with calcium phosphate crystals in bone

what is the ECM composition of vitreous humour

almost entirely GAG and little collagen

what does the hydrophilic nature of GAGs result in

they adopt extended conformations relative to their mass and therefore act as space fillers in connective tissue

what are some other, less common functions of proteoglycans

binding growth factors and controlling migration of cells through the ECM

what is an epithelium

a sheet of cells joined together side by side

what do epithelia cover

external surfaces and they line all internal cavities

what are the four main forms of epithelia

columnar, squamous, cuboidal, stratified

what are columnar epithelia used for

secretion, eg in the intestine

what are squamous epithelia used for

filtration, eg lining of the lung

what are cuboidal epithelia used for

secretion and absorption, eg lining of the kidney tubules

what are stratified epithelia used for

protection, eg epidermis of skin

what is the basal lamina

the mat like structure on which the sheet of epithelial cells sits, it is a thin and tough sheet of ECM

what does the basal lamina separate the epithelial cells from

the network of collagen fibres in the underlying connective tissue

what is ECM mostly composed of

type IV collagen and laminin

what supplies the collagen in ECM

underlying stromal cells

what supplies laminin in the ECM

the overlying epithelial cells

what does laminin provide in terms of integrin

provides adhesive sites for integrins located in the basal membrane of epithelial cells, it fulfils a linking role similar to that of fibronectin in connective tissue

what are the two faces of epithelial sheets

apical and basal

the apical epithelial sheet is

free and exposed to air or bodily fluids

the basal epithelial sheet is

attached to a sheet of connective tissue called the basal lamina

what is the function of tight junctions

helps the two epithelial cells to connect to each other, forming a barrier so substances in the lumen cannot move freely to the other side of the epithelial sheet

what proteins seal interacting cells in tight junctions

occludin and claudin

how do tight junctions help keep apical and basal domains of cells separate

by blocking the diffusion of membrane proteins

what is an example of a process that is possible due to the presence of tight junctions

transport of glucose against its concentration gradient in from the gut lumen and then down its concentration gradient out into the bloodstream