Quiralidad
Las moléculas como los aminoácidos son quirales, lo que significa que existen como isómeros ópticos de cada otro. Una molécula "quiral" (desde el Griego: χειρ, cheir[1], χειρός, cheiros, una mano) es una que no se puede superponer sobre su imagen especular. Así como las manos izquierda y derecha son imágenes especulares y no las mismas, las moléculas quirales tienen las mismas cosas unidas en la misma orden, pero de sentido opuesto una de la otra.
Las dos formas isoméricas de los (enantiómeros) de los aminoácidos son conocidas como las formas D y L.[2] Enantiomeric molecules are physically and chemically indistinguishable by most of the techniques available and only when probed asymmetrically, for instance, by plane-polarized light can they be distinguished.[1] Although most amino acids (except for glycine, which is non-chiral) can exist in both L and D forms, life on Earth is made of only L-form amino acids.[3] The L form is found in proteins. The D form is found in only some proteins that are formed by exotic sea dwelling organisms. No one knows why this is the case, but it offers strong evidence that life was designed rather than the result of random chemical evolution.
Like amino acids, ribose and deoxyribose sugars come in two chiralities but living things include only 'right-handed' sugars in its DNA or RNA.[2]
Discovery
In 1848, Louis Pasteur working as a chemist with a solution of synthetic ammonium tartrate tetrahydrate contaminated it with a mold and the solution became more optically active as the time passed.[4] For the first time anyone had demonstrated chiral molecules.
Formula Mass
The formula mass of any compound (ionic or molecular) is equal to the sum of the atomic masses of its constituent elements. If the compound is molecular, then the terms molecular mass or molar mass may properly describe this quantity.
Véase también
Referencias
- ↑ 1,0 1,1 Voet, Donald; Voet, Judith V (2011). Biochemistry (4ª edición). River Street, Hoboken, NJ: John Wiley & Sons. p. 74. ISBN 978-0470-57095-1.
- ↑ 2,0 2,1 Dembski, William A (2008). The Design of Life: Discovering Signs of Inteligence in Biological Systems. Dallas: The Foundation for Thought and Ethics. p. 227-228. ISBN 978-0-9800213-0-1.
- ↑ Plantilla:Citar livro
- ↑ Plantilla:Cite book
Enlaces externos
- Origin of life: the chirality problem by Jonathan Sarfati. TJ 12(3):263–266. December 1998
- Evolution Hopes You Don't Know Chemistry: The Problem with Chirality by Charles McCombs, Ph.D.
