What does the small amount of molecules with a free aldehyde mean in reactions
Easily oxidised
In too far
In the absence of H+ acetals are…
Stable
Because -OR is a poor leaving group
Reaction of D-glucose and methanol to make acetal formation - what is produced
- substitution reaction is reversible
- nucleophille can attach from either side of carbocation intermediate
- both a and b glycosides (acetals) are formed
a and b glycosides are…
Acetals
The pure glycosides dissolved in H20 in absence of strong acid are:
- stable
- no open chain form possible
- no reaction with Ag+
- NON REDUCING SUGARS
OH group used is glycoside formation can also be from
- another sugar
- larger carbohydrates contain glucose or other sugar units links together by glycosidic bonds
How can glycoside hydrolysis be acheived (glycoside hydrolysis)
- enzymatically
- H30+
Maltose is
A diasscaride with two glucoses linked together
Gylcosidic linkage in maltose is…
The glycosidic bond from c-1 (anomeric carbon) is pointing down while the CH2OH is up, thus an a-1,4-glycosidic linkage
Is maltose a reducing sugar?
- RH sugar contains a hemiacetal
- this is an equilibrium with the open chain aldehyde form of the right hand sugar
- thus maltose is a REDUCING sugar
- reducing sugar will work with tollens
What is cellobiose
- two glucose units linked though the same positions with a B-linkage (equatorial bond) produces a flatter structure
What is sucrose made up of and what forms
- made up of D-glucose and D-fructose linked together
- the D-glucose is in a phyranose form
- the D-fructose is in a furanose form
- non reducing - no hemiactely
Amylose - what kinds of bonds
- component of starch, polysaccharide of glucose units
- 4000 units joined together by a-1,4 glycosidic bonds in maltose
Structure of amylose and what happens in digestion
- helical 3D structure
- in digestion, a-amylose hydrolysed by enzyme (a-amylase) —-> glucose
Cellulose (polysaccride) type of bonds
- polymer of glucose with B-1,4 glycosidic bonds
Wood = 50% cellulose
Cotton = 100% cellulose
Geometry of cellulose B-1,4 glycosidic bonds
- geometry of these linkages leads to straight molecular rods established by a network of hydrogen bonds - useful for structural material
Digestion of cellulose
- mammals without a rumen cannot digest cellulose
- digestive enzymes have reactive sites which are the right shape for a-1,4’-glycosidic linkages
- B-1,4’-glycosidic links do not fit - CANNOT DIGEST CELLULOSE
Carbohydrates and molecular recognisiton
- large scope for variability
- many combinations that can give unique patterns on cell surfaces
Monosaccharides can differ in: - number of carbons
Strerochemistly
Functional groups
Ring sizes - furanose and pyranose
Orientation of groups - a and b
