DISACCHARIDES Flashcards
What do disaccharides yield on hydrolysis with dilute acids or enzymes?
Two molecules of either the same or different monosaccharides.
How are two monosaccharides in a disaccharide joined together?
By an oxide linkage formed by the loss of a water molecule.
What is the linkage between two monosaccharide units through an oxygen atom called?
Glycosidic linkage.
What are non-reducing disaccharides?
Disaccharides in which the reducing groups (aldehydic or ketonic) are bonded, such as sucrose.
What are reducing disaccharides?
Disaccharides in which the aldehydic or ketonic functional groups are free, such as maltose and lactose.
What monosaccharides are produced when sucrose is hydrolyzed?
An equimolar mixture of D-(+)-glucose and D-(-)-fructose.
How are glucose and fructose linked in sucrose?
By a glycosidic linkage between C1 of α-D-glucose and C2 of β-D-fructose.
Why is sucrose a non-reducing sugar?
Because the reducing groups of glucose and fructose are involved in glycosidic bond formation.
Is sucrose dextrorotatory or laevorotatory?
Sucrose is dextrorotatory.
What happens to optical rotation when sucrose is hydrolyzed?
It gives dextrorotatory glucose and laevorotatory fructose.
Why is the hydrolyzed mixture of sucrose laevorotatory?
Because the laevorotation of fructose (-92.4°) is greater than the dextrorotation of glucose (+52.5°).
What is the term for the change in optical rotation after sucrose hydrolysis?
It is called ‘invert sugar’ because the rotation changes from dextro (+) to laevo (-).
What monosaccharides make up maltose?
Two α-D-glucose units.
How are the glucose units in maltose linked?
By a glycosidic bond between C1 of one glucose and C4 of another glucose.
Why is maltose a reducing sugar?
Because the free aldehyde group can be produced at C1 of the second glucose in solution.
What is lactose commonly known as, and where is it found?
Lactose is commonly known as milk sugar and is found in milk.
What monosaccharides make up lactose?
β-D-galactose and β-D-glucose.
How are the monosaccharides in lactose linked?
By a glycosidic bond between C1 of galactose and C4 of glucose.
Why is lactose a reducing sugar?
Because a free aldehyde group can be produced at C1 of the glucose unit.
