Which one of the following statements is not true regarding (+) Lactos...
(+) lactose is a reducing sugar and it exhibit mutarotation
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Which one of the following statements is not true regarding (+) Lactos...
Lactose is a disaccharide sugar composed of two monosaccharides, namely D(+) glucose and D(+) galactose. It is commonly found in milk and dairy products. Let's analyze each statement to determine which one is not true:
a) Lactose, C12H22O11 contains 8-OH groups:
Lactose is composed of two monosaccharides, and each monosaccharide has several hydroxyl groups (-OH). Glucose has four hydroxyl groups, while galactose has six hydroxyl groups. Therefore, lactose, which is a combination of glucose and galactose, will have a total of ten hydroxyl groups. Hence, statement a) is true.
b) On hydrolysis, Lactose gives an equal amount of D(+) glucose and D(+) galactose:
Hydrolysis is the process of breaking a bond by adding water. When lactose undergoes hydrolysis, the bond between glucose and galactose is broken, resulting in the formation of one molecule of D(+) glucose and one molecule of D(+) galactose. Therefore, statement b) is true.
c) Lactose is a β-glycoside formed by the union of a molecule of D(+) glucose and a molecule of D(+) galactose:
Lactose is indeed a β-glycoside. It is formed by the linkage of the hydroxyl group on carbon-1 of glucose with the hydroxyl group on carbon-4 of galactose. Hence, statement c) is true.
d) Lactose is a reducing sugar and does not exhibit mutarotation:
This statement is not true. Lactose is a reducing sugar because it has a free anomeric carbon (carbon-1 of glucose) that can undergo oxidation. It can reduce certain reagents such as Benedict's solution or Fehling's solution. Additionally, lactose exhibits mutarotation, which is the spontaneous interconversion between α and β anomers in an aqueous solution. This occurs because the hemiacetal or hemiketal ring structure of the sugar can open and close, resulting in the formation of a new equilibrium mixture of α and β forms. Therefore, statement d) is false.
In conclusion, the correct answer is option D because lactose is a reducing sugar and exhibits mutarotation.
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