Biological Molecules

Which statement correctly describes the difference between α-glucose and β-glucose?

• They have different molecular formulas

• They differ in the position of the –OH group on carbon 1

• They differ in the position of the –OH group on carbon 4

• α-glucose is a monosaccharide while β-glucose is a disaccharide

Answer explanation

α-glucose and β-glucose differ in the orientation of the –OH group on carbon 1. In α-glucose, the –OH is below the plane, while in β-glucose, it is above. They have the same molecular formula, and both are monosaccharides.

In cellulose, β-glucose molecules are linked by:

• α-1,4 glycosidic bonds

• β-1,4 glycosidic bonds with alternating inversion of monomers

• β-1,6 glycosidic bonds

• α-1,6 glycosidic bonds

Answer explanation

In cellulose, β-glucose molecules are linked by β-1,4 glycosidic bonds, which involve alternating orientations of the glucose monomers, creating a linear structure that is crucial for its strength and stability.

Which carbohydrate is most highly branched?

• Amylose

• Amylopectin

• Glycogen

• Cellulose

Answer explanation

Glycogen is the most highly branched carbohydrate, with numerous branching points that allow for rapid mobilization of glucose. In contrast, amylose is unbranched, and amylopectin has fewer branches than glycogen.

The reaction that forms a glycosidic bond between two monosaccharides is:

• Hydrolysis, releasing a water molecule

• Condensation, releasing a water molecule

• Hydrolysis, requiring a water molecule

• Condensation, requiring a water molecule

Answer explanation

The formation of a glycosidic bond between two monosaccharides occurs through a condensation reaction, which releases a water molecule as a byproduct. This is the correct choice.

Which statement best explains why cellulose is suitable for providing structural support in plant cell walls?

• It has coiled chains for compact storage

• It has cross-linked hydrogen bonds between straight chains of β-glucose

• It contains α-1,6 branches for rapid hydrolysis

• It dissolves easily in water for quick transport

Answer explanation

Cellulose's structural support in plant cell walls is due to cross-linked hydrogen bonds between straight chains of β-glucose, providing rigidity and strength, unlike the other options which do not contribute to structural integrity.

Amylose differs from amylopectin in that amylose:

• Contains only α-1,4 glycosidic bonds and forms a helix

• Contains α-1,4 and α-1,6 glycosidic bonds and is branched

• Contains β-1,4 glycosidic bonds and is unbranched

• Contains β-1,6 glycosidic bonds and forms sheets

Answer explanation

Amylose is a linear polymer of glucose that contains only α-1,4 glycosidic bonds, allowing it to form a helical structure. In contrast, amylopectin has both α-1,4 and α-1,6 bonds, making it branched.

Which carbohydrate would be most rapidly hydrolysed to glucose in animals?

• Amylose

• Amylopectin

• Glycogen

• Cellulose

Answer explanation

Glycogen is the primary storage form of glucose in animals and is rapidly hydrolyzed by enzymes like glycogen phosphorylase, making it the quickest source of glucose compared to amylose, amylopectin, and cellulose.

The breakdown of a disaccharide into two monosaccharides involves:

• A condensation reaction and the release of water

• A hydrolysis reaction and the release of water

• A hydrolysis reaction and the use of water

• A condensation reaction and the use of water

Answer explanation

The breakdown of a disaccharide into two monosaccharides is a hydrolysis reaction, which involves the use of water to cleave the glycosidic bond, resulting in the formation of two monosaccharides.

The main storage carbohydrate in animals is:

• Amylose

• Amylopectin

• Glycogen

• Cellulose

Answer explanation

The main storage carbohydrate in animals is glycogen, which is a polysaccharide that serves as a form of energy storage. Amylose and amylopectin are plant starches, while cellulose is a structural component in plant cell walls.

Which feature is common to both glycogen and amylopectin?

• Both have β-1,4 glycosidic bonds

• Both have α-1,4 and α-1,6 glycosidic bonds

• Both form unbranched helical chains

• Both are found only in plants

Answer explanation

Glycogen and amylopectin both contain α-1,4 and α-1,6 glycosidic bonds, which are crucial for their structure and function. This allows them to form branched polysaccharides, unlike the other options listed.