Question | Answer |
What are the four major components of the extracellular matrix? | collagens, elastin, proteoglycans, and hyaluronans |
What is the structure of collagen? | primary subunits are left handed helices; these associate into right handed triple helices known as tropocollagens, which are bundled together to form collagen fibers |
What is the structure of elastin? | Tropoelastin polypeptides are synthesized in the rough ER and secreted to the extracellular space. Once there, they congretate to a scaffold of fibrillin |
What is the structure of proteoglycan? | glycosaminoglycans (GAGs) bound to a core protein; made of modified disaccharides |
What is the function of collagen? | provides tensile strength by resisting stretching |
What is the function of elastin? | provides tissues with elasticity, the ability to return to their original size and shape |
What is the function of proteoglycan? | help anchor cells to the basal lamina through crosslinking with other components of the ECM (sometimes collagen); sometimes function as regulators (such as heparin) as well |
Why are prolines important in collagen? | They contort the polypeptide backbone and forces it into a left handed helix |
Why are glycines important in collagen? | Their amino acid side chain is simply a hydrogen atom. This allows the helix to form. Larger side groups would cause steric hindrance. |
What is fibrosis? | excess collagen (build up of scar tissue) |
What causes scurvy? | lack of vitamin C which causes a decreased hydroxylation of proline residues |
Ehler's-Danlos Syndrome is a result of what? | underproduction or incomplete processing of different collagens |
Osteogenesis imperfecta (brittle-bone syndrome) is cause by... | a mutation of type I collagen; this interferes with triple helix assembly |
What amino acid crosslinking is seen in elastin? How many are bound together? | lysine; four |
Is elastin a bundle or a mesh network? | mesh network |
What gives elastin the ability to "snap back"? | interspersed hydrophobic and hydrophilic domains |
What condition are homozygous alpha1-AT mutants predisposed to? Why? | emphysema; because the elastin in the alveolar walls is degraded due to inhibition of elastase |
Fibrillin mutations result in... | Marfan's syndrome |
Where are proteoglycans often found? | plasma membrane |
What do proteoglycans sequester? | growth factors |
What are hyaluronans? | glycosaminoglycans (GAGs that are not bound to the core protein as is seen in proteoglycans) that interact with water molecules to form hydration spheres |
What is the function of hyaluronans? | resist compression and serve as lubricants for joints |
What is the function of aggrecans? | resistance of compression |
Where are aggrecans most prevalent? | cartilage |
What are the ECM crosslinking proteins? | lamin and fibernectin |