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 \(\beta-1,4\) -glycosidic bonds c. contains both \(\alpha-1,4\) - and \(\alpha-1,6\) -glycosidic bonds d. produces maltose during digestion

Short answer

a. Glycogen. b. Cellulose. c. Glycogen. d. Starch.

Step-by-step solution

Identify the polysaccharide for part (a)

The storage form of carbohydrates in animals is known as glycogen.

Identify the polysaccharide for part (b)

The polysaccharide that contains only \(\beta-1,4\) -glycosidic bonds is cellulose.

Identify the polysaccharide for part (c)

The polysaccharide that contains both \(\beta-1,4\) - and \(\beta-1,6\) -glycosidic bonds is glycogen.

Identify the polysaccharide for part (d)

The polysaccharide that produces maltose during digestion is starch.

Key concepts

Glycogen

Glycogen is the primary storage form of carbohydrates in animals.
It is similar to starch in plants, but it is more extensively branched. Glycogen is composed of glucose units linked together mainly by \(\alpha-1,4\)-glycosidic bonds, with branches formed by \(\alpha-1,6\)-glycosidic bonds.
This structure allows for quick release of glucose when energy is needed, which is crucial for maintaining blood sugar levels in animals. Glycogen is primarily stored in the liver and muscles.
In the liver, it helps to regulate blood glucose levels, while in muscles, it serves as an immediate energy source during physical activity.

Cellulose

Cellulose is a polysaccharide found predominantly in the cell walls of plants. It provides structural support to the plant cell. Unlike glycogen and starch, which are used for energy storage, cellulose is used for building and maintaining the structure of the plant.
Cellulose is composed of glucose units linked by \(\beta-1,4\)-glycosidic bonds. These bonds create long, straight chains that can hydrogen bond with each other, forming rigid structures.
Humans cannot digest cellulose due to the absence of the enzyme cellulase needed to break the \(\beta-1,4\) bonds, so it passes through the human digestive system as fiber, aiding in digestion.

Alpha and Beta Glycosidic Bonds

Glycosidic bonds are crucial in forming polysaccharides. There are two main types: alpha and beta.
An \(\alpha\)-glycosidic bond forms when the anomeric carbon of the glucose molecule is in the \(\alpha\) configuration. For instance, in starch and glycogen, glucose molecules are linked by \(\alpha-1,4\)-glycosidic bonds, and branching occurs via \(\alpha-1,6\) bonds. These bonds result in helical structures, making them easy to break down by enzymes for energy release.
On the other hand, a \(\beta\)-glycosidic bond forms when the anomeric carbon is in the \(\beta\) configuration. Cellulose is made up of glucose molecules linked by \(\beta-1,4\)-glycosidic bonds, creating straight chains. These are more difficult to break down, which is why humans can’t digest cellulose.

Starch

Starch is the primary storage form of carbohydrates in plants. It is a mixture of two polysaccharides: amylose and amylopectin.
Amylose is a helical polymer made of glucose units linked by \(\alpha-1,4\)-glycosidic bonds. Amylopectin, similar to glycogen but less branched, contains both \(\alpha-1,4\)- and \(\alpha-1,6\)-glycosidic bonds.
During digestion, enzymes break starch down primarily into maltose and glucose, which are then further broken down to provide energy. The structure of starch makes it an efficient storage molecule, and its helical chains are easily accessible to enzymes. This is why starch is a significant part of the human diet.