Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

2. Cell Chemistry & Cell Components

Carbohydrates

Anatomy & Physiology

2. Cell Chemistry & Cell Components

Carbohydrates

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2:12 minutes

Problem 6

Textbook Question

Although cellulose and starch are identical in terms of stored chemical energy, our ability to harvest the energy from these two polysaccharides differs considerably. What is responsible for this difference?

Verified step by step guidance

Understand the structure of cellulose and starch: Both are polysaccharides composed of glucose units, but they differ in the type of glycosidic bonds that link the glucose molecules.

Identify the type of glycosidic bonds: Starch is composed of α(1→4) and α(1→6) glycosidic bonds, while cellulose is composed of β(1→4) glycosidic bonds.

Consider the enzyme specificity: Human digestive enzymes, such as amylase, can break down α-glycosidic bonds in starch but cannot break down β-glycosidic bonds in cellulose.

Analyze the structural implications: The β(1→4) bonds in cellulose result in a linear, fibrous structure that is resistant to enzymatic digestion, whereas the α(1→4) bonds in starch create a helical structure that is more accessible to enzymes.

Conclude the reason for the difference: The inability of human enzymes to digest cellulose is due to the presence of β-glycosidic bonds, which are not recognized by these enzymes, unlike the α-glycosidic bonds in starch.

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Key Concepts

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

Polysaccharide Structure

Cellulose and starch are both polysaccharides made up of glucose units, but their structural configurations differ significantly. Starch consists of amylose and amylopectin, which are branched and can be easily broken down by enzymes. In contrast, cellulose has a linear structure with β-1,4-glycosidic bonds, making it resistant to enzymatic degradation in humans and many animals.

Enzymatic Breakdown

The ability to harvest energy from polysaccharides relies on specific enzymes that can break down their glycosidic bonds. Humans possess enzymes like amylase that can effectively hydrolyze starch, releasing glucose for energy. However, we lack the necessary enzymes, such as cellulase, to break down cellulose, which is why we cannot utilize its energy despite its abundance in plant materials.

Digestibility and Energy Harvesting

Digestibility refers to how well a substance can be broken down and absorbed by an organism. Starch is digestible and provides a readily available energy source, while cellulose is largely indigestible for humans. This difference in digestibility is crucial for understanding why we can efficiently harvest energy from starch but not from cellulose, despite their similar energy content.