Final answer:
True statement about amyloid protein structures is that they consist of stacked β sheets. These misfolded structures can aggregate into plaques that are associated with diseases like Alzheimer's, but they are not universally causing neurodegenerative diseases and are not made of helical fibers. (option c)
Step-by-step explanation:
The true statement about amyloid protein structures is: c) They consist of stacked β sheets. Amyloid proteins are misfolded forms of normal proteins, which normally exist in a soluble alpha-helix configuration. However, when they misfold, they form β-pleated sheets that are sticky and can aggregate into plaques, or amyloid structures. These alterations in their structure affect their functionality and can lead to them becoming toxic.
Examples of diseases associated with the accumulation of amyloid plaques include Alzheimer's and Creutzfeldt-Jakob disease. It's important to note that amyloid proteins do not always cause neurodegenerative diseases and they are not necessarily made up of helical protein fibers.
While amyloid plaques have a dense and ordered structure, they are not typically described as weak and brittle but are rather characterized by their stability and resistance to degradation.
Hence, the answer is option c