Chaperones are used for-
Correct Answer: Protein folding
Description: Ans. is 'a' i.e., Protein folding* Chaperones are proteins which help in folding or unfolding of proteins* Molecular chaperones prevent aggregation and promote refolding after stress and hence promote cell survival. This so-called stress response is ubiquitous and conserved across all organisms. Hence Chaperones are otherwise known as heat shock proteins (HSP)* Chaperones are synthesized in response to heat and other stress conditions like , exposure to heavy metals, UV radiation, oxidative stress, nutrient deficiencies, dehydration, osmotic pressures and viral infections. Hence, they are otherwise called as stress proteins* Heat shock proteins are evolutionarily conserved, abundant and ubiquitous proteins in all cells and play similar roles in organisms from bacteria to humans. They are amongst the most highly expressed and can account for 1-2 % of the total protein in unstressed cells, and this can increase up to 4-6 % after heat shock* Some chaperone systems work as foldases: they support the folding of proteins in an ATP-dependent manner (for example, the GroEL/GroES or the DnaK / DnaJ / GrpE system). Other chaperones work as holdases: they bind folding intermediates to prevent their aggregation, for example DnaJ or Hsp33* The human heat shock proteins have been renamed to the following: HSPH (former name HSP110), HSPC (HSP90), HSPA (HSP70), HSPD/E (HSP60/HSP10) and CCT (TRiC), DNAJ (HSP40), and HSPB (small HSP or sHSP)* Despite the fact that heat shock proteins differ in their size, structures and activity, they all bind non-native proteins (some bind native proteins as well); and some exert their functions co-translationally by interacting with nascent polypeptides, while others act post-translationally by providing an environment that enhances folding.* Most heat shock proteins are ATP-dependent and require ATP to control binding and dissociation of substrate polypeptides, while some use an ATP-independent mechanism.* Thus,# Chaperones are otherwise called as heat shock proteins. But not all heat shock proteins are chaperones. Heat shock proteins also perform some function other than protein folding.# Chaperones are not always ATP dependent.# Chaperones do not always bind to specific segments of polypeptide chain, some just provide the environment for protein folding.# Chaperones act as either foldases or holdases.
Category:
Biochemistry
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