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Chemistry of Sugars + Isomers (Importance (In metabolism: Sugars are the…
Chemistry of Sugars + Isomers
Importance
In metabolism: Sugars are the products of photosynthesis and are the source of carbon for most other biological molecules
Energy storage and transport
As components of other biological macromolecules such as DNA,glycoproteins or glycolipids
Structure
Unmodified simple sugars
Three to seven carbon atoms
All but one carbon has a hydroxyl group
remaining carbon has an aldehyde or ketone group. Sugar with an aldehyde are aldoses / ketones are ketoses
Electronegativity: Ability of an atom to attract electrons towards itself in a chemical bond
Bond energies: (to break the bond)
Single covalent 75-560 kJ mol-1
Ionic bonds >650 kJ mol-1 (in vacuum)
Hydrogen bonds 5-30 kJ mol-1
Van der waals interactions 0.4-4kJ mol-1
Sugars dissolve easily in water because of the partial charges on the -OH groups
Isomers
Different molecules with the same atomic composition
Most sugars have optical isomers
Stereoisomers
Molecules that differ only in the spatial arrangement of their atoms. All atoms are liked to the same number of the same types of atom by the same number of bonds
Optical isomers can be denoted as + or - depending on their effect on the angle of plane polarised light
Chiral atoms can also be denoted as R or S on the basis of the atomic weight of the atoms bonded to the carbon
No plane of symmertry
Enantiomer: Have same physical properties, usually have different biological properties
Achiral: A molecule that has a plane of symmetry in any of its possible conformations
Diastereomers
Molecules with more than one Chirality centre