Final answer:
The unfolded protein response is activated by an accumulation of unfolded or misfolded proteins in the ER, often due to increased protein synthesis, genetic mutations, or environmental stress like heat shock. Heat shock proteins are crucial for refolding misfolded proteins, as they are released from complexes and transcription of their genes is increased to cope with stress. The ubiquitination and proteasome systems also play a role by degrading irreversibly damaged proteins.
Step-by-step explanation:
The unfolded protein response (UPR) is activated when there is an accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). This response helps in maintaining cellular function by dealing with the stress of misfolded proteins. Heat shock proteins (HSPs) play a crucial role in this process by helping to refold misfolded proteins. In response to increased temperature, a situation that can cause proteins to unfold improperly, HSPs are released from the NR/HSP complex and transcription of HSP genes is increased.
There are several reasons why the unfolded protein response might occur:
- Increased protein synthesis that overwhelms the folding capacity of the ER.
- Genetic mutations that produce proteins that are prone to misfolding.
- Environmental stresses such as heat shock, oxidative stress, or heavy metals that can directly damage proteins or disrupt their folding.
While addressing heat shock, the cell increases the activity of proteins like HSPs because they assist in refolding misfolded proteins that can accumulate due to the stress. This process involves ubiquitination and proteasome-mediated degradation, which help remove irreversibly damaged proteins and prevent cellular toxicity.