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Georgia Lofts

Georgia Lofts

Email: georgialofts@gmail.com

Total Article : 144

About Me:I am a second year student studying BioMedical Science. I am interested in a wide range of topics but particularly like to focus on Biology, Art and Philosophy.

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The extracellular matrix

The extracellular matrix

BIOLOGY REVISION: THE EXTRACELLULAR MATRIX

 

First thing to know… it is very complex! So, let’s break it down a bit to make it a little easier to understand.

 

The extracellular matrix (ECM)

The material that surrounds animal cells

Produces a variety of structures (like bone, tendons, shells of molluscs)

Not just a structural role, it can regulate the behaviour of its resident cells

Abundant in connective tissue (CT) both loose and dense

Spaces around cells are filled with hydrated polysaccharide glycosaminoglycans often linked to proteins to form a proteoglycan gel

 

It influences the survival development, migration, shape, proliferation and function of the cells within it. Molecules of the ECM are produced locally (for example secreted by fibroblasts in loose connective tissues, by osteoblasts and chondroblasts in bone/cartilage respectively).

 

Glycosaminoglycan (GAGs)

Chains are repeated units of negatively charge disaccharides that form linear chains, and that attract cations (sodium) causing large amounts of water to be sucked into the matrix

Most can be linked to proteins to form proteoglycans

All GAGs and proteoglycans are synthesised in, and secreted by, cells in the ECM

 

GAGs and Proteoglycans

Varied nature means that pore sizes in the gel, and charge densities vary. This influences not only turgor(water), but also what cells may pass through the ECM

PGs can bind signalling molecules enhancing or inhibiting their activity to affect nearby cell proliferation slide 11

 

Like the GAGs and proteoglycans, these proteins are secreted by cells in the ECM (the secretory pathway is very active in these cells). Collagens/elastin give strength and resilience, and can be anchored by sticky fibronectin/laminin to the integrins of cells.

 

Fibroblasts in connective tissue

Showing cells (fibroblasts) and ECM proteins

It is mainly collagen fibres that are visible because the hydrated gel of GAGs and proteoglycans has been removed by enzyme and acid treatments in preparation for microscopy

Collagens

The most abundant proteins found in the animal kingdom

there are ~25 distinct alpha chains used in various combinations give 20 types of collagen.

There are 46 different collagen genes dispersed throughout the human genome

the main types in connective tissues are types I, II, III, V and XI – the fibrillar collagens. Each collagen trimer can cross-link to others to form fibrils

Types IX and XII are the fibril-associated collagens

Type IV forms a mesh in basal laminae

are trimeric (B) (3 chains of the same type)

characterised by a stiff triple stranded helical structure with lots of H- bonds between the 3 subunits

each hydrophobic polypeptide (α chain) is ~1,000 amino acids

they are predominantly synthesized by fibroblasts however epithelial cells are sometimes responsible

 

Fibrillar Collagens

 

made in cells as precursors (procollagen) with N- and C-terminal propetides that are not present in the mature extracellular collagen

these proteins undergo numerous modifications from their site of folding in the ER lumen to their deposition in the extracellular matrix

 

image- http://ib.bioninja.com.au/standard-level/topic-1-cell-biology/13-membrane-structure/extracellular-matrix.html                                                                                                                      

 

 

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