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Ch. 2 The Chemistry of Life
Amerman - Human Anatomy & Physiology 2nd Edition
Amerman2nd EditionHuman Anatomy & PhysiologyISBN: 9780136873822Not the one you use?Change textbook
All textbooksAmerman 2nd EditionCh. 2 The Chemistry of LifeProblem L3.1
Chapter 2, Problem L3.1

The polysaccharide cellulose is not digestible by humans, as we lack the enzyme cellulase, which is required to break it down. Certain dietary supplements contain the enzyme cellulase and claim that being able to break down cellulose will help a person lose weight. But what do you think would happen if we could digest the cellulose we ate?

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Understand the role of cellulose in the human diet: Cellulose is a polysaccharide made of glucose molecules linked by β-1,4-glycosidic bonds. Humans lack the enzyme cellulase, which is required to break these bonds, so cellulose passes through the digestive system as fiber, aiding in digestion and promoting gut health.
Consider the function of cellulase: If humans could digest cellulose using cellulase, the β-1,4-glycosidic bonds in cellulose would be broken down into glucose molecules, which could then be absorbed into the bloodstream and used as an energy source.
Analyze the potential impact on calorie intake: Since glucose is a source of calories, digesting cellulose would increase the caloric content of foods that contain cellulose. This could lead to an increase in energy intake rather than weight loss, unless the individual adjusts their overall diet to account for the additional calories.
Evaluate the claim of weight loss: The claim that digesting cellulose would help with weight loss is likely misleading. Instead of acting as a non-digestible fiber that aids in satiety and bowel health, cellulose would contribute to caloric intake, potentially leading to weight gain if not balanced with energy expenditure.
Reflect on the importance of fiber: Fiber, including cellulose, plays a critical role in maintaining digestive health, regulating blood sugar levels, and promoting a feeling of fullness. Digesting cellulose might reduce these benefits, which could negatively impact overall health.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cellulose

Cellulose is a complex carbohydrate or polysaccharide that forms the structural component of the cell walls in green plants, algae, and some fungi. It is composed of long chains of glucose molecules linked by β-1,4-glycosidic bonds, making it resistant to digestion by humans due to the absence of the enzyme cellulase. While cellulose is not digestible, it serves as dietary fiber, promoting digestive health.
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Enzymatic Digestion

Enzymatic digestion refers to the biochemical process where enzymes break down complex molecules into simpler ones, facilitating nutrient absorption. In the case of cellulose, the enzyme cellulase is necessary to hydrolyze the β-glycosidic bonds, allowing the body to utilize the glucose units. Without this enzyme, cellulose passes through the digestive system largely intact, contributing to fiber intake rather than energy.
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Impact on Weight Loss

The claim that digesting cellulose could aid in weight loss hinges on the idea that breaking down this polysaccharide would provide additional calories. However, if humans could digest cellulose, it might lead to increased caloric intake without a corresponding increase in satiety, potentially resulting in weight gain rather than loss. Additionally, the role of fiber in promoting fullness and regulating appetite would be compromised.
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Related Practice
Textbook Question

The drug methotrexate is used to treat several different types of cancer and diseases of the immune system. It works by inhibiting an enzyme in the cell necessary for folic acid synthesis. Without folic acid, the cell cannot make nucleotides. What, specifically, does an enzyme do in the cell? Why would inhibiting this enzyme disrupt folic acid synthesis? What effect would a disruption in folic acid synthesis have on the cell as a whole? (Hint: Think about the role that folic acid plays in the cell.) (Connects to Chapter 2)

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Textbook Question

Considering that water is a main component of the juices in the stomach and intestines, explain why digestion of lipids is more complicated than digestion of carbohydrates and proteins.

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Textbook Question

Explain how buffer systems in the body work if the pH of body fluids increases. Is this an example of a negative or a positive feedback loop? Explain.

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Textbook Question

Many drugs and poisons exert their effects by blocking one or more enzymes. How could blocking an enzyme lead to the death of a cell?

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Textbook Question

Which of the following statements correctly describes a solution?

a. In a solution the solute is chemically dissolved by the solvent.

b. Solutions involve large particles suspended in another component.

c. The particles in a solution will settle out if left to sit.

d. The amount of solute in a solution is expressed as the solution's concentration.

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