Regarding proteoglycans, false is:
Correct Answer: They hold less amount of water
Description: GAGs are generally associated with a small amount of protein forming proteoglycans which contain > 95% carbohydrate. Whereas, glycoproteins contain primarily protein & a small amount of carbohydrate.
All the GAGs, except hyaluronic acid, form proteoglycans. It is also the only GAG which is not sulfated and also found in bacteria.
Proteoglycan monomer resembles a bottle brush as it consists of a core protein to which linear GAG chains are covalently attached. Each chain may be composed of > 100 monosaccharide chains, remain separated from each other because of charge repulsion.
The GAGs present in the proteoglycans are polyanions and hence bind polycations and cations such as Na+ and K+. This latter ability attracts water by osmotic pressure into the extracellularmatrix and contributes to its turgor. GAGs also gel at relatively low concentrations.
Because of the long extended nature of the polysaccharide chains of GAGs and their ability to gel, the proteoglycans can act as sieves, restricting the passage of large macromolecules into the ECM but allowing relatively free diffusion of small molecules.
Again, because of their extended structures and the huge macromolecular aggregates they often form, they occupy a large volume of the matrix relative to proteins.
proteoglycan=GAGs + Protein (≤ 5%) = + proteins
Key Concept:
The GAGs present in the proteoglycans are polyanions and hence bind polycations and cations such as Na+ and K+. This latter ability attracts water by osmotic pressure into the extracellularmatrix and contributes to its turgor. Thus, they hold more amount of water.
Category:
Biochemistry
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