Summary of Reaction Types
Here is a list of the reaction types available to you.
- Aldol Cleavage
- Aldose-Ketose Isomerisation
- Ketose-Aldose Isomerisation
- Dehydration
- Phosphorylation
- Phosphoryl Shift
- Dephosphorylation
- Coupled Oxidation & Phosphorylation
- Oxidation
- Reduction
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Aldol Cleavage
An aldol is an aldehyde or ketone which has a hydroxyl group attached. In the diagram the black atoms are necessary for this reaction. The R groups may be hydrogen or extended carbon skeleton. Monosaccharides are aldols and can be subjected to this reaction. You should note that in the process one hydrogen atom is moved and a new aldehyde group is formed. When a monosaccharide is cleaved in this way the two products are both monosaccharides. The product with the blue R group must be an aldose. The other product, if a triose or larger will be a ketose. The Delta-G for the reaction will be near zero but there is a significant activation energy at physiological conditions which means the reaction requires an enzyme catalyst.
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Aldose-Ketose Isomerisation
An aldose is a monosaccharide with an aldehyde group. Common ketoses have a ketone group at carbon 2. It is possible for a hydrogen atom to be moved from one carbon atom to another and so convert an aldose into a ketose. The Delta-G for the reaction will be near zero but there is a significant activation energy at physiological conditions which means the reaction requires an enzyme catalyst.
Ketose-Aldose Isomerisation
Just the reverse of an aldose-ketose isomerisation. See above.
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Dehydration
Dehydration of an organic molecule is often in the form shown in the equation. An OH group is removed as a hydroxyl ion and a hydrogen attached to an adjacent atom is removed as a hydrogen ion. A double bond is formed as a result. It is not itself a reduction despite the removal of an oxygen atom but could be a prelude to reduction which would be implemented as a hydrogenation of the double bond.
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Phosphorylation
In the simplest form a phosphate group replaces the hydrogen of a hydroxyl group. The Delta-G for phosphorylation of an alcohol with inorganic phosphate is usually very positive and needs to be coupled with another process such as dephosphorylation of ATP.
The usual biochemical shorthand for the phosphate group is a P with a circle around it.
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Phosphoryl Shift
It is possible to remove a phosphate group from one hydroxyl group and put it on another using a single step. In fact it is easier for the enzyme to phosphorylate to a bisphosphate and then dephosphorylate. The net result is a phosphoryl shift. Phosphoryl shift is included here as a seperate reaction type because it can be acheived with a single enzyme.
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Dephosphorylation
In the simplest form a phosphate group is replaced with a hydrogen atom to give a hydroxyl group. The Delta-G for dephosphorylation of an alcohol is usually very negative and can be coupled with another energy requiring process such as phosphorylation of ADP.
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