Fibers and Junctions are a group of
related cellular components.  They
are each made of specific proteins
that interact to form a structure.
In the case of Junctions these
proteins cross between the membranes
of adjacent cells.   Not all cells
have all types of junctions. 
Unicellular organisms have none and
cells that remain singular such as
blood cells are also lacking
junctions.  As we will see other cell
types have those which are needed for
the functioning of that tissue. 

Fibers within the cell are caused by
the assembly of specific proteins. 
One unusual feature of this protein
interaction appears to be that under
different conditions the same protein
, for example tubulin, can form
several types of interactions leading
to the formation of several types of
organelles.