BIOLOGY 2B03 Lecture Notes - Lecture 18: Tight Junction, Cell Adhesion Molecule, Gap Junction
13 Jun 2018
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Cell Adhesion: Cell Adhesion Molecules
Multicellularity
development of multicellular organisms requires reiterated mitotic divisions to produce multiple cells •
during embryogenesis, as number of cells increases, they separate into 1 of 3 germ layers: •
endoderm ◦
ectoderm ◦
mesoderm ◦
cells must establish and maintain connections - otherwise would be soup •
cells from same species able to recognize and associate back together and cells from different species don't •
Embryonic Cell Association
cell specific •
Johannes Holtfreter performed experiment using frog embryo cells - took cells from 2 germ layers during •
development and separated individual cells
when cells mixed together, like ◦
tissue cells recognized/
associated - similar to how
originally were
but how? ◦
requires collection of •
transmembrane proteins that span
cell membrane called cell adhesion
molecules (CAMs)
cells form specialized cell junctions after aggregation that stabilize cell-cell interactions + facilitate •
communication between cells
Types of Junctions - Epithelial Cell
epithelial cells connect along lateral surfaces to form sheets to line body cavities •
many connections hold these cells together •
cells have apical/basal surfaces - basal anchored to extracellular structures •
adhesion complexes called hemidesmosomes connect cells to extracellular ◦
matrix
apical surface organized into microvilli facing interior of intestine •
4 types of adhesion complexes connect lateral surfaces: •
tight junctions ◦
adherents junctions ◦
desmosomes ◦
hemidesmosomes ◦
gap junctions ◦
Tight Junctions
connect adjacent epithelial cells below apical surface - seals off space •
between cells
prevents fluid movement across layer of cells - restricting diffusion of ◦
small molecules and prevents leakage of digestive enzymes
Freeze fracturing: cells frozen in liquid nitrogen and broken apart •
breaks at points of weakness and allows researchers to see network ◦
created by tight junctions
lines on image are linear arrays of tight junction proteins that criss-cross lateral surface of cells •
band between cells prevents diffusion of membrane proteins from apical to basolateral regions of plasma •
membrane - diffusion limited at tight junctions and molecules can't move further
