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A cell must continuously sort useful materials from its
waste products and then remove or recycle the waste. One
way a cell does this is to first put tiny tags on proteins that
are no longer needed. These tags, which are small
polypeptide chains 76 amino acids long, are called
ubiquitin.
Ubiquitin tags direct proteins to compartments of the cell
called proteasomes. Within each proteasome, ubiquitin-
tagged proteins are deconstructed into their component
amino acids. These pieces can be repurposed to build new
proteins.
Sometimes organs stop processing waste effectively,
allowing the waste to pile up and contributing to many
diseases. Alzheimer's disease, for example, includes piles
of waste proteins in the brain called tangles, while
Parkinson's disease involves the accumulation of recyclable
material into Lewy bodies. Mallory bodies are piles of waste
proteins common in liver disease. These piles, known
generically as inclusions, can be identified under the
microscope because they are covered in tiny ubiquitin tags.
A problem in the breakdown of ubiquitin-tagged proteins
may be one cause of soinocerebellar ataxia tvoe 1. In this
Why do individuals with spinocerebellar ataxia experience loss of
muscle control, even though the ataxin-1 protein builds up only in
the brain and spinal cord?
OA. Inclusions can build up in all body systems and can cause
debilitating effects.
OB. Genetic mutations in the ataxin-1 protein cause muscular
proteins to change shape.
OC. When the ubiquitin tagging system does not work
effectively, cellular waste can build up in the muscles.
OD. The neurons affected by the ataxin-1 protein buildup are
in a region of the brain that manages muscle control.