Urea acts as a chaotrope when in the presence of folded proteins and enzymes. It's not something you want floating about willy-nilly in your body. The structure of the molecule allows it to sow utter chaos:

/ \
../    \..
H2N      NH2

Those two pairs of electrons hanging out at the tail make the oxygen end of urea extremely electronegative and eager to bond. As it turns out, the hydrogen bonds that stabilize the outer shell of a folded protein are the perfect places to steal atoms from to solve urea's vexing problem. The chaotrope occupies hydrogen bonds, leaving the outer structure of the protein somewhat unstable. Hydrogen bonds are certainly not the only forces that hold together quaternary structure, however. The hydrophobic effect is also important, the desire of nonpolar portions of a protein to be as far away from surrounding water as possible, therefore rolling themselves into a little ball inside the protein.

Without the safety of a stable external structure to protect them, the hydrophobic portions of the molecule are soon assaulted with molecules of water worming their way inside. Once this happens, all bets are off. The protein increasingly loses every anchor point that allows it to maintain its distinctive shape; it denaturizes. What was once an extremely complex and useful association becomes nothing more than a chain of amino acids again.

U"re*a (?), a. [NL. See Urine.] Physiol. Chem.

A very soluble crystalline body which is the chief constituent of the urine in mammals and some other animals. It is also present in small quantity in blood, serous fluids, lymph, the liver, etc.

⇒ It is the main product of the regressive metamorphosis (katabolism) of proteid matter in the body, and is excreted daily to the amount of about 500 grains by a man of average weight. Chemically it is carbamide, CO(NH2)2, and when heated with strong acids or alkalies is decomposed into carbonic acid and ammonia. It unites with acids to form salts, as nitrate of urea, and it can be made synthetically from ammonium cyanate, with which it is isomeric.

Urea ferment, a soluble ferment formed by certain bacteria, which, however, yield the ferment from the body of their cells only after they have been killed by alcohol. It causes urea to take up water and decompose into carbonic acid and ammonia. Many different bacteria possess this property, especially Bacterium ureae and Micrococcus ureae, which are found abundantly in urines undergoing alkaline fermentation.<-- = urease -->


© Webster 1913.

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