Academics Andre's Research Biocuriosities Books Graduate School History of Science Hot off the Press Igor's Research Interdisciplinarity Molecule of the Month Open Access Philip's Research Philosophy of Science Physics Physicsworld.com
Backreaction Ceclia's Blog at PHD Comics Cocktail Party Physics Cosmic Variance The Daily Transcript Easternblot Everyday Scientist The Evilutionary Biologist Freelancing Science The Futile Cycle Good Math, Bad Math iMechanica in singulo Incoherently Scattered Ponderings Juniorprof Klara Stefflova Life of a Lab Rat The Loom Metadatta Mixed States Morning Coffee Physics Not Even Wrong Notes from the biomass Notional Slurry OpenScience Project Pharyngula PLoS Blog Ponderings of a fool Recombinants The Sandwalk SciAm Observations ScienceBlogs Scientific Clearing House Shtetl-Optimized Three-toed Sloth Uncertain Principles What's New by Bob Park
Molecular processes occur so fast that is it difficult to imagine a 24-hour clock that works at the molecular level. But surprisingly, different organisms have evolved many different ways of doing this. Animal cells use a complex collection of proteins (with fanciful names like Clock, Cryptochrome, and Period) that are rhythmically synthesized and degraded each day. The 24-hour oscillation of the levels of these proteins is controlled by a series of interconnected feedback loops, where the levels of the proteins precisely regulates their own production. A much simpler system has been discovered in cyanobacteria. It is composed of three proteins, KaiA, KaiB and KaiC, that together form a circadian clock. At the beginning of the cycle, KaiA (at the top, PDB entry 1r8j) stimulates the large KaiC hexamer (center, PDB entry 2gbl ), which then adds phosphate groups to itself. Then, as KaiC fills itself up with phosphates, it binds to KaiB (bottom, PDB entry 1r5p ), which inactivates KaiA and allows the phosphates to be slowly removed. As the number of phosphates drops, KaiB falls off and KaiA can start the cycle again.
See the rest at David Goodsell’s page, here.
Happy holidays! Edge World Question 2008: Things you have changed your mind about?
Biocurious is written by Andre Brown and Philip Johnson, since 2005. Content of the weblog is licensed under a Creative Commons Attribution-Share Alike 3.0 License.
