Q. 13.50 - An Introduction to General, Organic, and Biological Chemistry

Question

Give the name of one or more polysaccharides that matches each of the following descriptions:

a. the storage form of carbohydrates in animals

b. contains only $\beta (1\to 4)$-glycosidic bonds

c. contains both $alpha(1\to 4)$ - and $alpha(1\to 6)$-glycosidic bonds

d. produces maltose during digestion

Step-by-Step Solution

Answer

Part a) Glycogen is form of a glucose storage type in animals.

Part b) Cellulose contains only $\beta (1 \to 4)$ glycosidic bonds.

Part c) $\alpha (1 \to 4)$ and $\alpha (1 \to 6)$ glycosidic linkages are found in both amylopectin and glycogen.  

Part d) Amylose and amylopectin produce maltose during digestion. 

Step 1: Introduction about Polysaccharides (Part a)

• Polysaccharides are carbohydrates that include $10$or more monosaccharides.
• The glycosidic bond is the most important bond in polysaccharide structural stability. 
• These polysaccharides create more than $10$monosaccharide units after complete hydrolysis.

Step 2: Explanation (Part a)

• Glycogen is form of a glucose storage type in animals. 
• Glycogen a glucose polymer with a unique structure. 
• Branches with $a(1 \to 6)$-glycosidic links occur every $10$ to $15$ glucose units, though.
• It is a polysaccharide that is more branched than amylopectin.

Step 3: Explanation (Part b)

• In plants, cellulose is a primary structural carbohydrate. 
• The $beta(1 \to 4)$-glycosidic bond connects lengthy unbranched glucose units in cellulose.
• The enzyme $d$-amylase hydrolyzes $alpha(1 \to 4)$-glycosidic bonds in humans, but not $beta(1 \to 4)$-glycosidic bonds. 
• This is the reason that cellulose could not be digested by humans.

Step 4: Explanation (Part c)

• $\alpha (1 \to 4)$ and $\alpha (1 \to 6)$ glycosidic linkages are found in both amylopectin and glycogen. 
• $alpha-D$-glucose units are connected by $alpha(1 \to 4)$-glycosidic linkages in amylopectin and glycogen. amylopectin, and every $25$ to $30$ glucose units in glycogen.

Step 5: Explanation (Part d)

• Acid hydrolysis or amylase action of amylose and amylopectin produces smaller sugars known as dextrins. 
• These dextrins are further hydrolyzed by amylase to maltose. 
• Therefore, amylose and amylopectin produce maltose during digestion.