Question

Which of the following is digestible by humans and is made up of only one type of monosaccharide? (A) Lactose (B) Sucrose (C) Maltose (D) Cellobiose

Short answer

The correct answer is (C) Maltose.

Step-by-step solution

Understand the Question

Identify which substance is digestible by humans and consists solely of one type of monosaccharide.

Review the Options

Look at each option: (A) Lactose, (B) Sucrose, (C) Maltose, and (D) Cellobiose. Determine the composition of each.

Analyze Option A (Lactose)

Lactose is a disaccharide made up of glucose and galactose. It consists of two different types of monosaccharides.

Analyze Option B (Sucrose)

Sucrose is a disaccharide composed of glucose and fructose. It consists of two different types of monosaccharides.

Analyze Option C (Maltose)

Maltose is a disaccharide composed of two glucose molecules. It is made up of only one type of monosaccharide (glucose).

Analyze Option D (Cellobiose)

Cellobiose is a disaccharide composed of two glucose molecules linked differently from maltose, but still made up of one type of monosaccharide (glucose).

Determine Digestibility by Humans

Maltose is digestible by humans due to the enzyme maltase. Cellobiose is not digestible by humans as the enzyme to break it down is not present.

Choose the Correct Answer

Based on composition and digestibility, the correct answer is (C) Maltose.

Key concepts

Digestible Carbohydrates

Digestible carbohydrates are an essential part of our diet. They are carbohydrates that our body can break down and use for energy. These include sugars and starches, which can be converted into glucose, the primary energy source for our cells.
Understanding which carbohydrates are digestible is crucial for MCAT biochemistry questions. For instance:

• Starches from foods like potatoes and rice are digestible.
• Disaccharides like sucrose and lactose are broken down by specific enzymes into monosaccharides.
• Fiber, unlike other carbohydrates, is generally not digestible.

For humans, enzymes like amylase and maltase are critical for digesting carbohydrates. This enzymatic activity breaks down complex carbohydrates into simpler sugars that can be absorbed into the bloodstream.

Disaccharides

Disaccharides are carbohydrates made up of two monosaccharide molecules bonded together. They play a significant role in our diet and metabolism. Common disaccharides include:

• Lactose: Found in milk, composed of glucose and galactose.
• Sucrose: Common table sugar, made up of glucose and fructose.
• Maltose: Formed by two glucose units.

The structure of disaccharides affects their digestibility. Enzymes like lactase, sucrase, and maltase are necessary to break them down into their respective monosaccharides for absorption. For example, maltase acts on maltose, splitting it into two glucose molecules that can be readily absorbed. In people lacking specific enzymes, such as those with lactose intolerance, the respective disaccharides cannot be digested properly.

Monosaccharides

Monosaccharides are the simplest form of carbohydrates and are the building blocks of disaccharides and polysaccharides. They include:

• Glucose: The primary energy source for cells.
• Fructose: Found in fruits and used for energy.
• Galactose: Part of lactose in milk.

Monosaccharides are directly absorbed into the bloodstream during digestion. Because they do not need further breakdown, they provide a quick source of energy. In the context of MCAT questions, knowing the specific structures and sources of these sugars helps in identifying how they interact in metabolic pathways and how they are utilized by the body.

Enzyme Activity

Enzyme activity is crucial for the digestion and metabolism of carbohydrates. Enzymes are proteins that catalyze biochemical reactions, usually increasing the reaction rate. In carbohydrate digestion:

• Amylase: Breaks down starch into smaller sugars.
• Maltase: Converts maltose into two glucose molecules.
• Lactase: Breaks down lactose into glucose and galactose.

Each enzyme is specific to a particular substrate. For instance, maltase specifically acts on maltose and not on other disaccharides. This specificity ensures efficient digestion and absorption of nutrients. Enzyme deficiencies can lead to digestive issues, such as lactose intolerance, where lacking lactase enzyme causes difficulty digesting lactose. Understanding enzyme activity is fundamental in biochemistry and helps explain metabolic processes and digestion intricacies for MCAT examinations.