Proteasomes are very large protein complexes inside all eukaryotes and
archaea, as well as in some bacteria. In eukaryotes, they are located
in the nucleus and the cytoplasm. The main function of the proteasome
is to degrade unneeded or damaged proteins by proteolysis, a chemical
reaction that breaks peptide bonds. Enzymes that carry out such
reactions are called proteases. Proteasomes are part of a major
mechanism by which cells regulate the concentration of particular
proteins and degrade misfolded proteins. Proteins are tagged for
degradation with a considerably small protein called ubiquitin. The
tagging reaction is catalyzed by enzymes called ubiquitin ligases. Once
a protein is tagged with a single ubiquitin molecule, this is a signal
to other ligases to attach additional ubiquitin molecules. The result
is a polyubiquitin chain that is bound by the proteasome, allowing it
to degrade the tagged protein. The proteasomal degradation pathway is
essential for many cellular processes, including the cell cycle, the
regulation of gene expression, and responses to oxidative stress. The
importance of proteolytic degradation inside cells and the role of
ubiquitin in proteolytic pathways was acknowledged in the award of the
2004 Nobel Prize in Chemistry to Aaron Ciechanover, Avram Hershko and
Irwin Rose.
Read the rest of this article:
<http://en.wikipedia.org/wiki/Proteasome>
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Today's selected anniversaries:
1867:
The Manchester Martyrs were hanged in Manchester, England, for their
rescue of two Irish nationalists, who played important roles in the
failed Fenian Rising, from jail.
<http://en.wikipedia.org/wiki/Manchester_Martyrs>
1963:
The first episode of Doctor Who was broadcast on BBC television with
William Hartnell in the title role, starting a programme that
eventually became the world's longest-running science fiction on
television.
<http://en.wikipedia.org/wiki/Doctor_Who>
1971:
The People's Republic of China was given China's permanent seat on the
United Nations Security Council.
<http://en.wikipedia.org/wiki/China_and_the_United_Nations>
2007:
MS Explorer became the first cruise ship to sink in the Antarctic
Ocean.
<http://en.wikipedia.org/wiki/MS_Explorer>
2009:
At least 57 people, including 34 journalists, were killed in the
Maguindanao massacre in the Philippines.
<http://en.wikipedia.org/wiki/Maguindanao_massacre>
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Wiktionary's word of the day:
gestalt (n):
A collection of entities that creates a unified concept, configuration,
or pattern which is greater than the sum of its parts
<http://en.wiktionary.org/wiki/gestalt>
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Wikiquote quote of the day:
Old wood to burn! Old wine to drink! Old friends to trust! Old authors
to read!
--Alfonso X of Castile
<http://en.wikiquote.org/wiki/Alfonso_X_of_Castile>