Question 1

How does starch digestion begin when food enters the mouth?

Accepted Answer

Salivary amylase enzymes break down starch into smaller polymers as soon as food enters the mouth. This initial breakdown is crucial because amylase enzymes cannot function in the stomach's acidic environment. The partially digested starch then travels to the small intestine, where pancreatic amylases continue breaking it down into disaccharides like maltose and dextrin.

Question 2

What enzymes convert disaccharides into monosaccharides in the small intestine?

Accepted Answer

Brush-border cells of the small intestine secrete specific enzymes that metabolize disaccharides into monosaccharides. Beta-galactosidase breaks lactose into glucose and galactose, while sucrase hydrolyzes sucrose into glucose and fructose. These monosaccharides are then transported across the intestinal epithelium into the bloodstream for absorption by body cells.

Question 3

What happens to glucose once it enters a cell?

Accepted Answer

Once inside a cell, glucose enters glycolytic pathways where it is metabolized into pyruvate. This process is coupled with the production of energy molecules ATP and NADH. The role of reduced coenzymes NADH and FADH in energy production makes this process essential for cellular energy generation.

Question 4

How are galactose and fructose metabolized after absorption?

Accepted Answer

Galactose and fructose are converted to glucose-6-phosphate after absorption into body cells. Once converted, they enter glycolysis alongside glucose. This conversion allows these monosaccharides to participate in the same energy-producing metabolic pathways as glucose, ensuring efficient energy extraction from all dietary carbohydrates.

Question 5

Why can't humans digest cellulose despite consuming it?

Accepted Answer

Humans lack cellulase, the enzyme required to digest cellulose found in plant cell walls. Although cellulose cannot be broken down for energy, it provides dietary fiber that adds bulk to food and aids digestion by helping partially digested food move smoothly through the intestines.

Question 6

What causes type 2 diabetes and how does it develop?

Accepted Answer

Type 2 diabetes develops when cells become resistant to insulin effects. In response, the pancreas increases insulin secretion, but beta cells eventually become exhausted. Lifestyle factors such as poor diet, inactivity, and obesity greatly increase risk. In many cases, moderate weight loss, regular physical activity, and healthy diet can reverse the condition.

Question 7

What is the normal blood glucose range and what indicates poor metabolism?

Accepted Answer

Normal blood glucose levels range from 70-99 mg/dL. Any deviation from this range signals poor carbohydrate metabolism and a weak regulatory system. Dysfunction in insulin production, secretion, or target cell responsiveness can lead to diabetes mellitus, a condition affecting millions of adults and children in the United States.

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