Saturday, December 17, 2005

Patchy Structure of Cell Membranes

CELL BIOLOGY: ON THE PATCHY STRUCTURE OF CELL MEMBRANE: Modified: "In the Singer-Nicholson model, molecules are distributed randomly in two dimensions. But it is known from first principles and from experimental observation that non-randomness is the rule.

Regions of biased composition exist in membranes, and the environments of proteins vary, because it is highly improbable that interaction energies will match each other across all protein and lipid species in a membrane. Time-invariant complexes, transient associations and biased distributions could be assumed to be the norm. Evolutionary selection, ever blindly seeking to exploit the natural tendencies of molecules, has seized the opportunity to craft functional associations. It is clear that there are functional protein complexes, separated lipid compositional areas, and regions of functional specialization."
Saturday, December 03, 2005

ABC proteins

Purdue Biologists Clarify How A Cellular 'Spacecraft' Opens Its Airlock: "ABC proteins function like tiny tweezers and are powered by ATP, a chemical that animal cells use for energy. When ATP causes the tweezers to squeeze shut, the membrane proteins open to reveal a small cavity that can hold a nutrient or other substance the cell requires from the outside. Once the nutrient is in place, the cell uses water to break down the ATP, signaling the 'tweezers' to relax, closing the membrane protein gate and capturing the nutrient. Lastly, the membrane protein releases the nutrient into the cell's interior."
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