Chapter 6, Problem 46A

Summary Introduction

To write:

Why humans cannot digest all carbohydrates.

Introduction:

Carbon forms the component of all living organisms. Life on earth is thus said to be carbon-based. The compounds that contain carbon are known as organic compounds. Carbon can form four covalent bonds with other atoms. These covalent bonds allow carbon to bonds to each other, giving rise to a variety of important carbon compounds. The carbon compounds can exist as straight chains, branched or ring structure. Carbon compounds lead to diversity of life on earth.

Explanation of Solution

Carbohydrates are compounds composed of carbon, hydrogen, and oxygen. Carbohydrates are grouped into monosaccharides, disaccharides and polysaccharides. Biologically important carbohydrates are called simple sugars or monosaccharides. Glucose is a monosaccharide that plays a central role in providing energy. Monosaccharides are joined to form disaccharides. Sucrose, present in sugar, and lactose found in milk are disaccharides. Glycogen is a polysaccharide that is found in the liver and skeletal muscles and is stored as an energy form of glucose. Glycogen is broken down into glucose when the body requires energy between meals, or during physical activity. In plants the structural support is provided by a carbohydrate called cellulose. Cellulose is a polymer of linear polysaccharide, with several monosaccharide glucose units. The acetal linkage in cellulose is beta which distinguishes it from starch. This unique variation in acetal bonding results in a substantial difference in human digestibility. Human beings are unable to digest cellulose because there are no sufficient enzymes for breaking down beta-acetal linkages.

Conclusion

Human beings are able to digest most carbohydrates, except for dietary fiber and resistant starches.