Extracellular matrix, cell adhesion and cell junctions
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Course
Biomedical Science 1st Year Cell Biology #1
Institution
Kings College London (KCL)
What is the extracellular matrix and what are its components? Explanation of tight junctions and gap junctions. What are hemidesmosomes and desmosomes and how cells interact with each other?
Extracellular matrix, cell adhesion and cell
junctions:
Introduction:
Cells are organized into tissues. In some tissues, such as bone or tendon, extracellular
matrix is plentiful and mechanically all-important; in others, such as
muscle or epidermis, extracellular matrix is scanty, and the cytoskeletons
of the cells themselves carry the mechanical load. Simplified drawing of a cross section through part
of the wall of the intestine of a mammal.This long, tubelike organ is constructed from epithelial
tissues, connective tissues, and muscle tissues. Each tissue is an organized assembly of cells, held
together by cell–cell adhesions, extracellular matrix, or both.
Cell junction complexes allow cells to adhere with each other or with extracellular matrices.
Collagen is a protein found in all animals, and it comes in many varieties. Mammals have about 20 different collagen genes,
coding for the variant forms of collagen required in different tissues. Collagens are the chief proteins in bone, tendon, and
skin, and they constitute 25% of the total protein mass in a mammal—more than any other type of protein.
Some types of collagen molecules in turn assemble into ordered polymers called collagen fibrils, which are thin cables 10–
300 nm in diameter and many micrometers long; these can pack together into still thicker collagen fibers. Other types of
, collagen molecules decorate the surface of collagen fibrils and link the fibrils to one another and to other components in the
extracellular matrix.
The connective-tissue cells that manufacture and inhabit the extracellular matrix go by various names according to the tissue:
in skin, tendon, and many other connective tissues, they are called fibroblasts, in bone, they are called osteoblasts. They
make both the collagen and the other macromolecules of the matrix.
the cells can secrete collagen molecules in a precursor form, called procollagen, with additional peptide extensions at each
end that obstruct premature assembly into collagen fibrils. Extracellular enzymes—called procollagen proteinases—cut off
these terminal extensions to allow assembly only after the molecules have emerged into the extracellular space.
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