Question 1

Which is a reducing sugar with an α-glycosidic linkage?

Accepted Answer

Maltose is a reducing sugar because it has a free anomeric carbon with an α-glycosidic linkage, which can open up and participate in a reducing sugar reaction. Sucrose has a glycosidic linkage between glucose and fructose, but it is not a reducing sugar because both anomeric carbons are involved in the glycosidic linkage. Lactose has a β-glycosidic linkage, which cannot open up to participate in a reducing sugar reaction. Cellobiose has an β-glycosidic linkage and cannot participate in a reducing sugar reaction.

Question 2

Compound X is a reducing sugar which,on hydrolysis,affords two molar equivalents of D-glucose.This hydrolysis is catalyzed by an enzyme specific for glucosides of this type:  What is the identity of X?

Accepted Answer

Maltose is a disaccharide composed of two glucose units joined by an α(1→4) bond. On hydrolysis, maltose yields two molar equivalents of D-glucose. The enzyme specific for glucosides of this type is maltase. Therefore, compound X is most likely maltose. The other options, such as sucrose, lactose, and cellobiose, do not yield two molar equivalents of D-glucose on hydrolysis, and their respective enzymes are not specific for glucosides of this type.

Question 3

Which of the following is the structure of D-galacturonic acid?

Accepted Answer

The answer of Which of the following is the structure...

Question 4

Many carbohydrates exist in equilibrium with cyclic hemiacetals.Those carbohydrates that form a five-membered cyclic hemiacetal are called _____________.

Accepted Answer

The answer of Many carbohydrates exist in equilibrium with cyclic...

Question 5

Which monosaccharide is recovered from the hydrolysis of glycogen?

Accepted Answer

Glycogen is a polysaccharide composed of glucose monomers linked by alpha 1-4 glycosidic bonds with alpha 1-6 glycosidic bond branching every 8-12 glucose units. Hydrolysis of glycogen breaks down these bonds, releasing glucose monomers. Therefore, the monosaccharide recovered from the hydrolysis of glycogen is D-glucose.

Question 6

The simplest carbohydrates (those that cannot be hydrolyzed to simpler carbohydrates)are called ______________.

Accepted Answer

The answer of The simplest carbohydrates (those that cannot be...

Question 7

Consider the structures below.An L-aldohexose,X,is treated with nitric acid to yield an optically inactive aldaric acid.The same L-aldohexose,X,is subjected to a Ruff degradation and the degradation product is oxidized with nitric acid to produce an optically inactive aldaric acid.Which is a possible structure for X?

Accepted Answer

The answer of Consider the structures below.An L-aldohexose,X,is treated with...

Question 8

Cellulose lacks nutritive value for humans because:

Accepted Answer

Humans lack the enzymes that can catalyze the hydrolysis of the glycosidic linkages in cellulose. As a result, the products of its digestion are excreted without utilization, and cellulose lacks nutritive value for humans.

Question 9

A monosaccharide containing six carbon atoms and an aldehyde functionality is called an _____________.

Accepted Answer

The answer of A monosaccharide containing six carbon atoms and...

Question 10

Carbohydrates are synthesized in green plants by _____________.

Accepted Answer

The answer of Carbohydrates are synthesized in green plants by...

Question 11

Which of these is an example of a glucan?

Accepted Answer

Amylose is an example of a glucan, which is a type of polysaccharide made up of glucose units. Glucans can be linear or branched and are found in various forms in nature. Amylose, specifically, is a linear form of glucose polymer found in starch.

Question 12

α-D-Glucose has [α]_D = +112^o,and β-D-glucose has [α]_D = +19^o.If either anomer is dissolved in water and allowed to reach equilibrium,the specific rotation of the solution is + 52^o.What are the percentages of each anomer at equilibrium?

Accepted Answer

The answer of α-D-Glucose has [α]_D = +112^o,and β-D-glucose has...

Question 13

Cellulose differs from chitin in which way?

Accepted Answer

Cellulose contains only D-glucose units while chitin contains only N-acetyl-D-glucosamine units. Option A is incorrect as the glycosidic linkages are different in both. Option C and D are incorrect as cellulose can be hydrolyzed and both cellulose and chitin have a linear structure. Option E is incorrect as chitin chains can be branched.

Question 14

Carbohydrates that hydrolyze to give a large number of molecules of monosaccharides are called _____________.

Accepted Answer

The answer of Carbohydrates that hydrolyze to give a large...

Question 15

The D-glucose unit at the branching point of amylopectin has free hydroxyl groups at which positions?

Accepted Answer

The answer of The D-glucose unit at the branching point...

Question 16

What is the correct description of this disaccharide?

Accepted Answer

The answer of What is the correct description of this...

Question 17

An aldopentose,X,is subjected to a Kiliani-Fischer synthesis to produce two aldohexoses,Y and Z.Both Y and Z,when oxidized with nitric acid,yield optically active aldaric acids.Which structure represents X?

Accepted Answer

The answer of An aldopentose,X,is subjected to a Kiliani-Fischer synthesis...

Question 18

Lactose exists in two forms α and β.Anomer α has [α]_D = +92.6^o,and anomer β has [α]_D = +34^o.What are the percentages of each anomer at equilibrium when the specific rotation of the water solution is + 52^o?

Accepted Answer

The answer of Lactose exists in two forms α and...

Question 19

Which of the following would yield D-glucose and D-mannose when subjected to a Kiliani-Fischer synthesis?

Accepted Answer

The answer of Which of the following would yield D-glucose...

Question 20

Which monosaccharide is recovered from the hydrolysis of starch?

Accepted Answer

Starch is a polysaccharide made up of glucose monomers. When it undergoes hydrolysis, it breaks down into individual glucose molecules. Therefore, the monosaccharide recovered from the hydrolysis of starch is D-glucose.

Quiz 22: Carbohydrates