Podcast
Questions and Answers
Which of the following sugars is considered a non-reducing sugar?
Which of the following sugars is considered a non-reducing sugar?
All monosaccharides are reducing sugars.
All monosaccharides are reducing sugars.
True
What color change occurs when iodine is added to a starch solution?
What color change occurs when iodine is added to a starch solution?
Blue-black
Reducing sugars can reduce soluble blue copper sulphate to insoluble red-brown _____.
Reducing sugars can reduce soluble blue copper sulphate to insoluble red-brown _____.
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Match the following tests with their purpose:
Match the following tests with their purpose:
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What is the expected result of adding Benedict's reagent to a non-reducing sugar solution?
What is the expected result of adding Benedict's reagent to a non-reducing sugar solution?
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Starch is classified as a monosaccharide.
Starch is classified as a monosaccharide.
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What type of carbohydrate does Barfoed's test differentiate?
What type of carbohydrate does Barfoed's test differentiate?
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Study Notes
Carbohydrate Scheme
- Carbohydrates are a subject of medical biochemistry and molecular biology at Menoufia University.
- Learning outcomes include classifying carbohydrates, differentiating between sugar types, and performing chemical tests to identify sugars.
Physical Properties of Carbohydrates
- Volume is a random sample.
- Taste is sweet (except starch).
- Aspect is clear (except starch which is turbid).
- Odour is odourless.
- Reaction is neutral.
- Colour is colourless (except starch which is greyish white).
Carbohydrate Classification
- Carbohydrates are classified into simple sugars and complex carbohydrates.
- Simple sugars are further classified into monosaccharides and disaccharides.
- Complex carbohydrates are classified as polysaccharides.
Molisch's Test
- Used to detect any carbohydrate.
- Procedure: Add 2ml of 0.5% sugar solution in a test tube, add 2 drops of α-naphthol and mix. Add 2ml of concentrated sulfuric acid.
- Results: A violet ring will form between the layers.
Principle of Molisch's Test
- In the presence of concentrated sulfuric acid, sugars dehydrate forming furfural (in pentoses) or hydroxymethylfurfural (in hexoses).
- These compounds condense with α-naphthol to produce colored condensation products.
Iodine Test
- Used to differentiate between simple sugars (monosaccharides and disaccharides) and polysaccharides (e.g., starch).
- Procedure: Add a few drops of iodine solution to 2ml of carbohydrate solution.
- Results: Simple sugars show no colour change (yellow), while polysaccharides (starch) turn blue-black.
Fehling and Benedict Test
- Used to differentiate between reducing and non-reducing sugars.
- All monosaccharides and disaccharides are reducing sugars, except sucrose.
- Polysaccharides are non-reducing.
Fehling/Benedict Procedure
- Procedure: Add 1ml of carbohydrate solution to 5ml of Benedict's reagent and heat.
- Results: Non-reducing sugars produce no red precipitate. Reducing sugars produce a red precipitate.
Principle of Fehling/Benedict Test
- Reducing sugars reduce the soluble blue copper sulfate in the Fehling/Benedict reagent to insoluble red-brown copper oxide.
Barfoed's Test
- Used to differentiate between monosaccharides and disaccharides.
- Procedure: Add 1ml of sugar solution to 3ml of Barfoed's reagent and heat in a boiling water bath for 5 minutes.
- Results: Monosaccharides produce a red precipitate faster than disaccharides.
Principle of Barfoed's Test
- Barfoed's reagent is a solution of cupric acetate in dilute acetic acid.
- In an acidic medium, Barfoed's reagent reacts with monosaccharides faster than disaccharides, generating cuprous oxide.
Ketose and Seliwanoff's Tests
- Used to distinguish between ketoses (e.g., fructose) and aldoses (e.g., glucose).
- Principle: Detect the presence of a ketone group.
Seliwanoff's Test Procedure
- Procedure: Add 1ml of carbohydrate solution to 3ml of Seliwanoff's reagent, then boil in a water bath.
- Results: Ketoses (fructose/sucrose) give a cherry-red colour, while aldoses (glucose) show no colour change.
Ketose Test Procedure
- Procedure: Add 2ml of carbohydrate solution to 2ml of concentrated HCl and boil.
- Results: Ketoses (fructose/sucrose) produce a deep red colour, while aldoses (glucose) show no colour change.
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Description
This quiz covers the classification, physical properties, and chemical tests for carbohydrates, essential topics in medical biochemistry at Menoufia University. You will learn about simple and complex carbohydrates, their characteristics, and procedures like Molisch's test for detection. Test your knowledge on this fundamental subject!
