The extracellular space in tissues contains an intricate network composed of two major classes of macromolecules: the glycosaminoglycan-protein assemblages known as proteoglycans and fibrous proteins including collagen as well as elastin, fibronectin and laminin.
Collagen is the most abundant protein in the human body, making up approximately one third of the body's protein content. The structure and synthesis of collagen are important in first semester biochemistry, and, as such, this material needs to get a share of attention for the new MCAT. The transformation of tropocollagen into collagen and the mechanism of hydroxylation of lysine and proline residues are subjects which are especially easy to envision as MCAT passages.
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Conceptual Vocabulary for Connective Tissue Proteins
Connective Tissue Proteins
Collagen is the main structural protein in the extracellular matrix found in the various connective tissues of the body.
Fibrils, not to be confused with fibers or filaments, are structural biological materials tending to have diameters ranging from 10-100 nanometers.
Elastin is a key protein of the extracellular matrix. It is highly elastic and present in connective tissue allowing many tissues in the body to resume their shape after stretching or contracting.
The extracellular matrix is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide structural and biochemical support to surrounding cells.
Elastic fibers are an essential component of the extracellular matrix composed of bundles of proteins (elastin) which are produced by a number of different cell types including fibroblasts, endothelial, smooth muscle, and airway epithelial cells.
A fibroblast is a type of biological cell that synthesizes the extracellular matrix and collagen, produces the structural framework (stroma) for animal tissues, and plays a critical role in wound healing.
Vitamin C (also known as ascorbate) is a vitamin found in various foods and sold as a dietary supplement. It is used to prevent and treat scurvy.
The basement membrane is a thin, pliable sheet-like type of extracellular matrix, that provides cell and tissue support and acts as a platform for complex signalling.
Hydroxyproline is produced by hydroxylation of the amino acid proline by the enzyme prolyl hydroxylase.
Ground substance is an amorphous gel-like substance in the extracellular space that contains all components of the extracellular matrix except for fibrous materials such as collagen and elastin.
Procollagen peptidase is an endopeptidase involved in the processing of collagen. The proteases removes the terminal peptides of the procollagen.
Lysyl oxidase catalyzes the conversion of lysine molecules into highly reactive aldehydes that form cross-links in extracellular matrix proteins.
Fibronectin is a high-molecular weight (~500 kDa) glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins.
One of the three main classification of protein structure (alongside globular and membrane proteins), scleroproteins (also called fibrous proteins) are made up by elongated or fibrous polypeptide chains which form filamentous and sheet like structure.