Diferencia entre revisiones de «Quiralidad»
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Molecules like amino acids are '''chiral''', meaning they exist as optical [[isomers]] of each other. A "chiral" molecule (from the {{Greek Name|χειρ|cheir}}<ref name=bio>{{cite book|author=Voet, Donald; Voet, Judith V|title=Biochemistry|edition=4th|publisher=John Wiley & Sons|page=74|location=River Street, Hoboken, NJ|year=2011|isbn=978-0470-57095-1}}</ref>, {{Greek Name2|χειρός|cheiros}}, a hand) is one that can not be superimposed on its mirror image. Just as left and right hands are mirror images and not the same, chiral molecules have the same things attached in the same order, but opposite of each other. | Molecules like amino acids are '''chiral''', meaning they exist as optical [[isomers]] of each other. A "chiral" molecule (from the {{Greek Name|χειρ|cheir}}<ref name=bio>{{cite book|author=Voet, Donald; Voet, Judith V|title=Biochemistry|edition=4th|publisher=John Wiley & Sons|page=74|location=River Street, Hoboken, NJ|year=2011|isbn=978-0470-57095-1}}</ref>, {{Greek Name2|χειρός|cheiros}}, a hand) is one that can not be superimposed on its mirror image. Just as left and right hands are mirror images and not the same, chiral molecules have the same things attached in the same order, but opposite of each other. | ||
| − | The two isomeric forms ([[enantiomer|enantiomers]]) of [[amino acids]] are known as the D and L forms. 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.<ref name=bio /> 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.<ref>{{citar livro|autor=Sarfati, Jonathan|autorlink=Jonathan Sarfati|título=[[By Design]]|editora=Creation Book Publishers|ano=2008|local=Australia|página=175|isbn=978-0-949906-72-4}}</ref> 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 [[Abiogenesis|chemical evolution]]. | + | The two isomeric forms ([[enantiomer|enantiomers]]) of [[amino acids]] are known as the D and L forms.<ref name=bydesign>{{cita libro|autor=Dembski, William A|enlaceautor=William Dembski|título=The Design of Life: Discovering Signs of Inteligence in Biological Systems|editorial=The Foundation for Thought and Ethics|ubicación=Dallas|año=2008|página=227-228|isbn=978-0-9800213-0-1}}</ref> 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.<ref name=bio /> 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.<ref>{{citar livro|autor=Sarfati, Jonathan|autorlink=Jonathan Sarfati|título=[[By Design]]|editora=Creation Book Publishers|ano=2008|local=Australia|página=175|isbn=978-0-949906-72-4}}</ref> 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 [[Abiogenesis|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.<ref name=bydesign /> | ||
==Discovery== | ==Discovery== | ||
Revisión del 11:30 1 nov 2013
Molecules like amino acids are chiral, meaning they exist as optical isomers of each other. A "chiral" molecule (from the Plantilla:Greek Name[1], Plantilla:Greek Name2, a hand) is one that can not be superimposed on its mirror image. Just as left and right hands are mirror images and not the same, chiral molecules have the same things attached in the same order, but opposite of each other.
The two isomeric forms (enantiomers) of amino acids are known as the D and L forms.[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.
See Also
References
Related references
- 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.
- ↑ 1,0 1,1 Plantilla:Cite book
- ↑ 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
