10 topics with brief reviews: definitions, key facts, and class questions.
The extracellular matrix is not just an inert tissue "glue", but a complex, dynamic system. In this section, we examine its key molecular components: structural proteins (collagen and elastin), as well as adhesive glycoproteins (fibronectin and laminin) responsible for cell-environment interactions.
Carbohydrate components hold a special place—glycosaminoglycans (primarily hyaluronic acid) and proteoglycans—which provide tissue turgor and resilience. The matrix is constantly remodeled: matrix metalloproteinases are responsible for its cleavage and turnover. Impairments in the biosynthesis of structural proteins lead to severe pathologies. A classic example we examine in detail is scurvy, caused by a defect in collagen hydroxylation due to vitamin C deficiency.
Colloquia and examinations focus heavily on the intracellular and extracellular stages of collagen assembly, the differences in its amino acid composition compared to elastin, and the structural principles of proteoglycans. Without this foundational knowledge, understanding the pathogenesis of connective tissue diseases in senior years is impossible.
Why does vitamin C deficiency impair collagen synthesis?
Ascorbic acid is required as a cofactor for prolyl hydroxylase. It maintains iron in its active ferrous ($Fe^{2+}$) state, without which the formation of hydroxyproline and a stable triple helix is impossible.
Why do blood vessels rupture in scurvy?
Vitamin C deficiency impairs hydroxyproline synthesis, hydrogen bonds fail to form, and collagen becomes unstable and denatures. This makes the vascular wall extremely fragile.
What are the main causes of low collagenase activity in healthy tissues?
The enzyme is synthesized as an inactive procollagenase, is strictly controlled by specific TIMP inhibitors, and is secreted exclusively in specific locations (compartmentalization) only when needed.
Due to the hydrophobic effect. In the stretched state, non-polar amino acids contact water, which is energetically unfavorable (entropy decreases). Upon load release, they tend to "hide" back into the coil.
Due to the hydrophobic effect. In the stretched state, abundant non-polar amino acids contact water, which is energetically unfavorable (entropy decreases). Upon load release, they tend to "hide" back inside the disordered globule.
Why do glycosaminoglycans carry a negative charge?
The negative charge is provided by the presence of hexuronic acid residues (glucuronic or iduronic) in their structure, as well as sulfate groups in most representatives.
Why is hyaluronic acid classified as a glycosaminoglycan rather than a proteoglycan?
Because its molecule consists exclusively of carbohydrate polymer chains and lacks a protein core, which is an obligatory component of proteoglycans.
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