cell-cell junctions (L24)

what are the 4 types of cell junctions

tight junctions

cell-cell anchoring junctions (adherens + desmosomes)

channel forming junctions (gap junctions)

cell-matric anchoring junctions (actin-linked cell-matric adhesion + hemidesmosomes)

what are the 2 actin linked junctions

adherens + focal adhesion

what are the features of adherens junctions

strong linked between actin cytoskeletons with cadherins

Ca2+ dependent

homophillic interaction

how does the adhesion belt affect morphogenesis

organised tightning along adhesion belts in selected regions of the cell sheet causes invagination of the epithelial sheet, epithelial tube can pinch off from overlying sheet of cells

what are the differences between hemidesmosomes and desmosomes

desmosomes attach cells-cells while hemidesmosomes attach cells-basal lamina

desmosomes involve cadherins + intermediate filaments (keratin filaments) while hemidesmosomes involve integrins + intermediate filaments

what causes pemphigus

autoimmune skin blistering

immune system attacks desmoglein which holds keratinocytes together in the epidermis

what is the role of tight junctions

to prevent fluid, ion, and membrane flow/ regulate paracellular flow

what is the structure of a tight junction

sealing strands of occludin + claudin proteins

zona occludens proteins bind claudins, occludins, + actin

(one type of occludin is conserved + found in all tight junctions while there are 20 types of claudins which make differnt tight junctions)

what are gap junctions

100-500nm long

close (not as close at tight junctions) apposition of membranes -gap of 2-4nm,

allows regulated + direct cell-cell communication

form 1.5nm diameter pores

allow movement of water, inorganic ions, sugars, AAs, ATP, cAM, IP3

what is the structure of a gap junction

made of connexins- channels composed of 6 subunits

two connexons in register form an open channel between adjacent cells

how are gap junctions regulated

Ca2+ is toxic so localisation needs to be regulated:

dopamine closes gap junctions + kills neuron, preventing damage to surrounding cells/neurones