The glyceraldehyde is a aldotriose whose formula is C 3 H 6 O 3 . It has two optical isomers, since it has an asymmetric carbon. Its importance is due to the fact that it is the first monosaccharide obtained in photosynthesis, during the dark phase (Calvin cycle)
Summary
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- 1 Glyceraldehyde triphosphate
- 2 Physical properties
- 3 Fischer projection
- 4 Nomenclature
- 5 External links
- 6 Sources
Glyceraldehyde triphosphate
The net result of the first phase of the glycolytic pathway is the conversion of one glucose molecule into two glyceraldehyde-triphosphate molecules; The second phase begins with the oxidation of glyceraldehyde-triphosphate in what, from the energy point of view, is one of the most important stages of the glycolytic pathway, since it conserves the oxidation energy of the aldehyde group of glyceraldehyde-triphosphate in its 1,3-bisphosphoglycerate product. The oxidation of glyceraldehyde-triphosphate drives both the reduction of the NAD + coenzyme and the subsequent phosphorylation of ADP.
Physical properties
- Density 1,455 kg / m3; 1,455 g / cm3
- Molar mass 90.08 g / mol
- Melting point 145 K (-128.15 ° C)
- Boiling point 140-150 K (-283.15 ° C)
Glyceraldehyde (2,3-dihydroxy-1-propanal) has an asymmetric carbon since it has the four dintint substituents, which gives rise to two stereoisomers of the molecule. The R isomer, also called D, and the S isomer, also called L.
The reality is that both enantiomers are molecules with different physicochemical properties and while L-glyceraldehyde deflects the plane of polarized light to the left (-), D-glyceraldehyde deflects the plane of polarized light to the right, ( +).
Fischer projection
In these representations for tetrahedral systems, the substituents that point outward from the image plane (toward the viewer) are in the horizontal positions, while those that point inward (opposite the viewer) are in the vertical positions. Also, the most rusty position is placed on top of the horizontal projection.
Fischer projection
Sugars with 4, 5, 6, and 7 carbon atoms are called tetroses, pentoses, hexoses, and heptoses, respectively. A molecule with n asymmetric centers and no plane of symmetry can have 2n stereisomeric forms. In these sugars that have more than one asymmetric center, the D or L nomenclature refers to the absolute configuration of the last carbon atom, according to the nomenclature used for glyceraldehyde. The following figure gives the names and Fischer projections of the tetroses, pentoses, and hexoses generated from D-glyceraldehyde. In red the asymmetric carbon that gives the monosaccharide its name is marked D, in a conformation identical to that of glyceraldehyde, and in green the C1 aldehyde is indicated. The numbering of the different carbons is in blue.
Nomenclature
The most frequent case of absence of plane of symmetry is due to the fact that some tetrahedral carbon is attached to four different radicals. This carbon is called asymmetric carbon. To represent the asymmetric carbons in a plane, several conventional projection representations have been devised. The most widely used is Fischer’s. According to this convention, the molecule is projected onto the plane of the paper with the following conditions:
1º.- The carbon chain is placed vertically, with the valences that make it up towards the back of the plane.
2º.- The chain is oriented with the most oxidized part up and the smallest part down.
3º.- Valences that do not make up the carbon chain are horizontal and directed towards the front of the plane
When this convention is applied, the D-isomer is the one that has the functional group to the right of the viewer and the L-isomer is the one that has it to the left: in sugars, the OH- 1 group of the penultimate carbon (as it is the asymmetric carbon furthest from the aldehyde or ketone group) in amino acids is considered a functional group to the amino group (NH 2 ) of the second carbon (carbon a)
The DL nomenclature does not indicate whether the compound is clockwise or left-handed. In the case of glyceraldehyde, the D-isomer is dextrorotatory, and is indicated by the (+) sign, but this does not always have to be the case.
The DL nomenclature is unambiguous to designate the configuration of isomers with a single asymmetric carbon. However, when there are several centers of asymmetry in a molecule, it is more convenient to use the system proposed by Cahn, Ingold and Prelog.
