Carbohydrate Analysis Quiz

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Questions and Answers

In Benedict's test, which color change most accurately indicates the presence of reducing sugars?

  • Blue to green
  • Yellow to orange
  • Red to brown
  • Blue to reddish (correct)

Barfoed’s test is primarily used to differentiate between which types of carbohydrates?

  • Reducing and non-reducing sugars
  • Monosaccharides and disaccharides (correct)
  • Monosaccharides and polysaccharides
  • Aldoses and ketoses

A positive Seliwanoff’s test, indicated by a red color, denotes the presence of which type of carbohydrate?

  • Reducing sugars
  • Ketoses (correct)
  • Aldoses
  • Starch

What is the primary function of Molisch's test in carbohydrate analysis?

<p>To identify carbohydrates from other macromolecules (B)</p> Signup and view all the answers

Which characteristic accurately describes carbohydrates?

<p>They consist of polyhydroxy aldehydes or ketones. (A)</p> Signup and view all the answers

Which of the following accurately describes a characteristic of polysaccharides?

<p>They can contain more than nine monosaccharide units. (B)</p> Signup and view all the answers

What is the main role of D-glucose in the human body?

<p>It serves as a primary energy source. (D)</p> Signup and view all the answers

Which statement correctly differentiates between reducing and non-reducing sugars?

<p>Reducing sugars can act as reducing agents due to the free anomeric carbon. (B)</p> Signup and view all the answers

What defines the classification of carbohydrates based on complexity?

<p>It groups carbohydrates as monosaccharides, disaccharides, oligosaccharides, and polysaccharides. (A)</p> Signup and view all the answers

Which laboratory technique is used for carbohydrate analysis?

<p>Benedict's test (A)</p> Signup and view all the answers

What is the general chemical formula for most carbohydrates?

<p>(CH2O)n (A)</p> Signup and view all the answers

Which of the following describes monosaccharides?

<p>They contain only one sugar unit. (D)</p> Signup and view all the answers

The process of breaking down complex carbohydrates into simpler sugars is known as:

<p>Hydrolysis (B)</p> Signup and view all the answers

Which of the following statements is true regarding reducing sugars?

<p>Lactose is an example of a reducing sugar due to its exposed carbonyl group. (D)</p> Signup and view all the answers

What characterizes polysaccharides in terms of their solubility in water?

<p>Polysaccharides form colloidal solutions in water. (C)</p> Signup and view all the answers

Which test is specifically used to distinguish between monosaccharides and disaccharides?

<p>Barfoed’s Test (B)</p> Signup and view all the answers

What color complex does starch form in the iodine test?

<p>Blue-black (D)</p> Signup and view all the answers

Which of the following carbohydrates cannot be identified using Molisch's Test?

<p>All carbohydrates can be identified using this test. (D)</p> Signup and view all the answers

Why are large polymers of glucose, such as starch, considered non-reducing sugars?

<p>They have no exposed carbonyl groups available for reduction. (B)</p> Signup and view all the answers

What type of sugar does Bial’s Test specifically detect?

<p>Pentose monosaccharides (C)</p> Signup and view all the answers

Which reducing sugar type reacts the fastest?

<p>Reducing monosaccharides (B)</p> Signup and view all the answers

Which statement about Benedict's Test is correct?

<p>It is used to detect the presence of reducing sugars. (C)</p> Signup and view all the answers

Which of the following best describes the reactivity of free anomeric carbons?

<p>They can react with oxidizing agents. (D)</p> Signup and view all the answers

What is produced when pentoses react with Bial's reagent?

<p>A bluish or green product (D)</p> Signup and view all the answers

Seliwanoff's test is primarily used to distinguish between which types of sugars?

<p>Aldoses and ketoses (C)</p> Signup and view all the answers

What color indicates the presence of ketoses in Seliwanoff's test?

<p>Cherry red (C)</p> Signup and view all the answers

Which reagent is a component of Bial's test for detecting pentoses?

<p>Orcinol (A)</p> Signup and view all the answers

In glucose test strips, elevated glucose levels in urine typically suggest what condition?

<p>High blood sugar (C)</p> Signup and view all the answers

What is the main purpose of Benedict's test?

<p>Identify reducing sugars (A)</p> Signup and view all the answers

What is indicated by a yellow to faint pink color in Seliwanoff's test?

<p>Aldoses reacting slowly (B)</p> Signup and view all the answers

What does Molisch's test specifically detect?

<p>Reducing sugars (D)</p> Signup and view all the answers

Which of the following best describes the reaction times of reducing monosaccharides compared to disaccharides?

<p>Monosaccharides react faster than disaccharides (D)</p> Signup and view all the answers

What is the primary purpose of Seliwanoff's Test?

<p>To distinguish between aldoses and ketoses (C)</p> Signup and view all the answers

Which reagents are used in the Molisch test to detect carbohydrates?

<p>Concentrated sulfuric acid and α-naphthol (B)</p> Signup and view all the answers

What visual indicator is observed in the Molisch test to confirm the presence of carbohydrates?

<p>A purple ring at the interface (B)</p> Signup and view all the answers

Which type of sugar does Benedict's test specifically identify?

<p>Reducing sugars (D)</p> Signup and view all the answers

What is the result of the reaction in Benedict's test when a reducing sugar is present?

<p>Formation of a reddish precipitate (C)</p> Signup and view all the answers

In Barfoed’s test, which sugars are identified based on their reaction speed?

<p>Monosaccharides react quickly, disaccharides react slowly (D)</p> Signup and view all the answers

What does the cupric ion do in Barfoed’s test?

<p>Oxidize reducing sugars to carboxylic acids (C)</p> Signup and view all the answers

Which carbohydrate is specifically identified as a non-reducing sugar in these tests?

<p>Sucrose (A)</p> Signup and view all the answers

What occurs when molisch’s reagent is added to the sample in the Molisch test?

<p>Formation of a colored ring (C)</p> Signup and view all the answers

Why must sulfuric acid be added slowly in the Molisch test?

<p>To allow time for carbohydrates to dehydrate (A)</p> Signup and view all the answers

Flashcards

What are carbohydrates?

Polyhydroxy aldehydes or ketones, commonly with the formula (CH2O)n, used as a source of energy for the body.

Monosaccharide

Simple sugars containing one monosaccharide unit. Examples are glucose and fructose.

Disaccharide

Complex sugars containing two monosaccharide units. Examples are sucrose and lactose.

Oligosaccharide

Complex sugars containing 3-9 monosaccharide units.

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Polysaccharide

Complex sugars containing more than 9 monosaccharide units. Examples are starch and cellulose.

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Hydrolysis

The process of breaking down complex carbohydrates into smaller sugar units.

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Reducing sugar

Sugars that can act as reducing agents. They have a free anomeric carbon that can react.

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Non-reducing sugar

Sugars that do not have a free anomeric carbon and cannot act as reducing agents.

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What is Molisch's test?

A test that uses Molisch's reagent to identify the presence of carbohydrates in a sample.

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What is Seliwanoff's test?

A test that distinguishes between aldoses and ketoses. It detects the presence of ketoses.

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What is Benedict's test?

A test that uses Benedict's reagent to identify reducing sugars, which have a free anomeric carbon that can react.

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What are reducing sugars?

Sugars that have a free anomeric carbon and can act as reducing agents.

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What are non-reducing sugars?

Sugars that do not have a free anomeric carbon and cannot act as reducing agents.

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What is Barfoed's test?

A test that uses Barfoed's reagent to identify the presence of reducing sugars, specifically differentiating between monosaccharides (which react quickly) and disaccharides (which react more slowly).

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What is a monosaccharide?

A carbohydrate with a single sugar unit, such as glucose or fructose.

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What is a disaccharide?

A carbohydrate with two sugar units, such as sucrose or lactose.

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What is hydrolysis?

The process of breaking down complex carbohydrates into smaller sugar units, typically by adding water.

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What is a mutarotation?

The chemical reaction that causes a change in the structure of a sugar molecule, often involving the rearrangement of atoms.

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Do all disaccharides act as reducing sugars?

Disaccharides like lactose have an exposed carbonyl group, making them reducing sugars, while others like sucrose don't have an exposed carbonyl and are non-reducing.

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Why are large polymers of glucose like starch not reducing sugars?

Polysaccharides, like starch, are not reducing sugars because their glucose units are linked together and don't expose a free aldehyde or ketone group for reduction reactions to occur.

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How do monosaccharides and disaccharides dissolve in water?

Monosaccharides and disaccharides can be dissolved in water due to their polar properties. Water, being a polar molecule, readily interacts with their polar groups.

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Why are polysaccharides less soluble in water than monosaccharides and disaccharides?

Polysaccharides are large molecules with high molecular weight, making them less soluble in water. Instead of fully dissolving, they form colloidal solutions, where they are dispersed but not fully dissolved.

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Explain the principle of the iodine test for polysaccharides.

The iodine test uses the property of polyiodide ions to form colored adsorption complexes with starch, dextrin, or glycogen due to the presence of glucose residues. This distinguishes these polysaccharides from monosaccharides and disaccharides.

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What are the color changes observed in the iodine test with starch, dextrin, and glycogen?

The iodine test can distinguish between polysaccharides like starch, dextrin, and glycogen, which turn blue-black, violet, or reddish-brown, respectively, from monosaccharides and disaccharides, which remain colorless.

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What is the purpose of the Molisch's test?

Molisch's test is a general test for the presence of carbohydrates. It uses a specific reagent to detect the presence of carbohydrates in a sample, regardless of their specific type.

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What is the purpose of the Benedict's test?

Benedict's test is used specifically to detect reducing sugars. It relies on the reducing property of these sugars to react with the Benedict's reagent and produce a colored precipitate, indicating their presence.

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How does Barfoed's test distinguish between monosaccharides and disaccharides?

Barfoed's test, another test for reducing sugars, differentiates between monosaccharides and disaccharides based on reaction speed. Monosaccharides react quickly, while disaccharides react more slowly, resulting in a visible difference.

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What color change in Benedict's test indicates reducing sugars?

In Benedict's test, a color change from blue to red indicates the presence of reducing sugars.

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What types of carbohydrates does Barfoed's test differentiate between?

Barfoed's test differentiates between monosaccharides and disaccharides by their reaction speed. Monosaccharides react quickly, leading to a red precipitate, while disaccharides react more slowly.

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What does a red color in Seliwanoff's test indicate?

Seliwanoff's test helps distinguish between aldoses and ketoses. A red color indicates the presence of a ketose.

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What is Molisch's test used for?

Molisch's test identifies the presence of carbohydrates by using Molisch's reagent.

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What is a reducing sugar?

A reducing sugar is a sugar that can act as a reducing agent. It has a free anomeric carbon that can react, leading to a change in the Benedict's reagent.

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What is Bial's test used for?

A chemical test that uses Bial's reagent to differentiate between pentose and hexose monosaccharides. It detects the presence of pentoses, which react to produce a bluish or green product.

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What is Seliwanoff's test used for?

A chemical test that uses Seliwanoff's reagent (resorcinol and HCl) to distinguish between aldoses and ketoses. It detects the presence of ketoses, which react quickly to produce a cherry red product.

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What are glucose test strips used for?

Glucose test strips are used to measure the amount of glucose (sugar) in a person's urine. They are helpful for monitoring glucose levels in individuals with diabetes.

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What is Benedict's test used for?

Benedict's test is a chemical test that utilizes Benedict's reagent to detect the presence of reducing sugars. Reducing sugars react to form a colored precipitate, ranging from green to red.

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How do reducing monosaccharides and disaccharides differ in reaction rates?

Monosaccharide reducing sugars react quickly in tests like Barfoed's test, while disaccharide reducing sugars react much slower.

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What is Barfoed's test used for?

A chemical test that uses Barfoed's reagent to differentiate between monosaccharides and disaccharides. It detects the presence of monosaccharides, which react quickly to produce a red precipitate.

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Study Notes

Course Information

  • Faculty of Medicine
  • Academic Year: 2024-2025
  • Year: 1
  • Module: Human Body Function (HBF) 102
  • Module Code: 102

Carbohydrate Chemistry Lab

  • Lab: Carbohydrates chemistry (Lab 2)
  • Lecturer: Dr. Hanaa B. Atya
  • Department: Biochemistry & Molecular Biology
  • Objectives:
    • Understand the structure, function, and classification of carbohydrates (monosaccharides, disaccharides, polysaccharides).
    • Gain hands-on experience in carbohydrate analysis techniques (e.g., Benedict's test, Barfoed's test).
    • Develop the ability to analyze and interpret experimental data, drawing conclusions about the presence and concentration of carbohydrates in lab results.

Carbohydrate Introduction

  • Carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones.
  • Most carbohydrates in the human body have the formula (CH₂O)ₙ.
  • Simple sugars end with an aldehyde or ketone group.

Carbohydrate Classification

  • Complexity:
    • Simple carbohydrates (one unit): Monosaccharides
    • Complex carbohydrates (more than one unit):
      • Disaccharides
      • Oligosaccharides
      • Polysaccharides
  • Size:
    • Tetroses (4 carbons)
    • Pentoses (5 carbons)
    • Hexoses (6 carbons)
    • Heptoses (7 carbons)
  • C=O Function:
    • Aldoses (aldehyde group)
    • Ketoses (ketone group)
  • Reactivity:
    • Reducing sugars (oxidized by Tollens' reagent, Benedict's reagent or Fehling's reagents)
    • Non-reducing sugars (not oxidized by those reagents)

A - Classification based on Complexity

  • Simple sugars (one unit): Monosaccharides.
  • Complex sugars (more than one):
    • Disaccharides (two monosaccharide units)
    • Oligosaccharides (3-9 monosaccharide units)
    • Polysaccharides (more than 9 monosaccharide units)
  • Complex carbohydrates can be broken down into smaller units through hydrolysis.

B - Classification based on Reactivity

  • Reducing sugars: The anomeric carbon's oxygen is not attached to any other structure. They can act as reducing agents.
  • Non-reducing sugars: The anomeric carbon's oxygen is attached to another structure. They cannot act as reducing agents.

Solubility of Sugars

  • Monosaccharides and disaccharides are freely dissolved in water due to its polarity
  • Polysaccharides are not freely dissolved in water because their high molecular weight forms colloidal solutions.

Iodine Test

  • The test distinguishes mono- and disaccharides from certain polysaccharides (starch, dextrin, glycogen).
  • Polyiodide ions form colored adsorption complexes with glucose residues of polysaccharides.
  • Monosaccharides, disaccharides, and unbranched polysaccharides are colorless in presence of iodine.

Chemical Properties

  • Molisch's Test: To identify carbohydrates from other macromolecules (lipids, proteins).
  • Benedict's Test: To detect reducing sugars.
  • Barfoed's Test: To distinguish between monosaccharides and disaccharides (based on reaction time), detecting reducing sugars.
  • Bial's Test: To distinguish between pentoses and hexoses (detecting pentoses).
  • Seliwanoff's Test: To differentiate between aldoses and ketoses (detecting ketoses).

Experiment 1: Molisch's Test

  • Objective: Identify carbohydrates from other macromolecules (lipids, proteins).
  • Principle: Acid dehydrates the sugar and reacts with alpha-naphthol to produce a purple product.

Experiment 2: Benedict's Test

  • Objective: Distinguish between reducing and non-reducing sugars.
  • Principle: Cu²⁺ in alkaline medium oxidizes reducing sugars (leading to color change).

Experiment 3: Barfoed's Test

  • Objective: Distinguish between monosaccharides and disaccharides (in terms of reaction time)
  • Principle: Cu²⁺ in slightly acidic medium reacts with reducing sugars and forms cuprous oxide

Experiment 4: Bial's Test

  • Objective: Differentiate between pentoses and hexoses.
  • Principle: Bial's reagent dehydrates pentoses to form furfural, which reacts further to produce a bluish or green product.

Experiment 5: Seliwanoff's Test

  • Objective: Distinguish between aldoses and ketoses.
  • Principle: Ketohexoses react faster with Seliwanoffs reagent to form cherry red products while aldoses to form yellow/pink products.

Glucose Test Strips

  • Measure glucose (sugar) in a person's urine.
  • Monitor glucose levels in people with diabetes.

Practical Work

  • Two biological samples will be provided (A & B).
  • Test for the presence of glucose using the tests.

Interactive Questions

  • Questions related to monosaccharides, disaccharides, carbohydrates, and the different tests.

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