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Questions and Answers
What is the purpose of dividing the mixture into two parts in the Xanthoproteic Test?
What is the purpose of dividing the mixture into two parts in the Xanthoproteic Test?
- To accurately measure the pH of the solution.
- To remove any precipitate that may have formed during heating.
- To ensure complete cooling before adding ammonia.
- To have a reference for comparing the color change after adding ammonia. (correct)
What is the role of concentrated sulfuric acid ($H_2SO_4$) in the Aldehyde Test for Tryptophan?
What is the role of concentrated sulfuric acid ($H_2SO_4$) in the Aldehyde Test for Tryptophan?
- It provides an acidic environment necessary for the formation of the violet color.
- It helps to dissolve the formaldehyde completely in the protein solution.
- It neutralizes any excess formaldehyde, preventing unwanted side reactions.
- It acts as a catalyst to speed up the reaction between formaldehyde and tryptophan. (correct)
In the Sakaguchi Test for Arginine, what is the purpose of adding bromine water?
In the Sakaguchi Test for Arginine, what is the purpose of adding bromine water?
- To dissolve the naphthol in the protein solution.
- To act as a catalyst for the reaction between naphthol and arginine.
- To neutralize the sodium hydroxide, ensuring the reaction proceeds at a controlled pH.
- To oxidize arginine, leading to the formation of a colored product. (correct)
What is the function of lead acetate ($Na_2S$) in the Test for Sulfur?
What is the function of lead acetate ($Na_2S$) in the Test for Sulfur?
A student performs the Xanthoproteic Test but forgets to add strong ammonia after cooling. What would be the likely outcome?
A student performs the Xanthoproteic Test but forgets to add strong ammonia after cooling. What would be the likely outcome?
In Millon's Reaction, what does the formation of a red or pink color indicate?
In Millon's Reaction, what does the formation of a red or pink color indicate?
Why is it important to add sodium hydroxide before bromine water in the Sakaguchi test?
Why is it important to add sodium hydroxide before bromine water in the Sakaguchi test?
What is the purpose of boiling the protein solution with NaOH in the test for Sulfur?
What is the purpose of boiling the protein solution with NaOH in the test for Sulfur?
A protein solution does not produce a purple color after undergoing the Ninhydrin test. What is the most likely explanation for this?
A protein solution does not produce a purple color after undergoing the Ninhydrin test. What is the most likely explanation for this?
In the Test for Tyrosine with Phenol Reagent, what is the role of sodium carbonate?
In the Test for Tyrosine with Phenol Reagent, what is the role of sodium carbonate?
Flashcards
Ninhydrin Test
Ninhydrin Test
Detects amino acids and proteins. Purple color indicates a positive result.
Xanthoproteic Test
Xanthoproteic Test
Detects tyrosine, tryptophan, and phenylalanine. Yellow to orange color indicates a positive result.
Millon's Reaction Test
Millon's Reaction Test
Detects tyrosine. Red or pink color indicates a positive result.
Aldehyde Test for Tryptophan
Aldehyde Test for Tryptophan
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Sakaguchi Test for Arginine
Sakaguchi Test for Arginine
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Test for Sulphur
Test for Sulphur
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Test for Tyrosine with Phenol Reagent
Test for Tyrosine with Phenol Reagent
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Study Notes
- Various tests are used to identify specific amino acids or proteins based on characteristic reactions
Ninhydrin Test
- Add 0.5cm³ of 0.1% ninhydrin to 2cm³ of test solution.
- Heat in boiling water for 10-15 minutes.
- A positive result is indicated by development of a purple color.
Xanthoproteic Test
- Heat 1cm³ of protein solution with 2cm³ of concentrated nitric acid until the mixture boils vigorously.
- Observe for a light yellow color to develop.
- Cool thoroughly and divide the solution into two parts.
- To one part, carefully add strong ammonia until the mixture turns alkaline.
- Note any intensification of yellow color.
- Use the other half as a control for comparison.
Millon's Reaction Test for Tyrosine
- Add 2-3 drops of Millon's reagent to 3cm³ of the protein solution and heat.
- A positive result is indicated by the formation of a red or pink color.
Aldehyde Test for Tryptophan
- To 2cm³ of protein solution, add 1 drop of dilute formaldehyde (1/500) followed by 2cm³ of very pure concentrated H₂SO₄.
- A positive test is indicated by development of a violet color at the junction of the two layers.
Sakaguchi Test for Arginine
- To 3cm³ of the protein solution, add a drop or two of naphthol in alcohol, 1cm³ of 5% sodium hydroxide, and 2-3cm³ of bromine water all at once.
- A positive result is indicated by the development of a pink color.
Test for Sulfur (Cysteine and Cystine)
- Boil 1cm³ of protein solution with 1cm³ of 20% NaOH for at least 3 minutes.
- Cysteine and cystine sulfur is split off and forms Naâ‚‚S.
- Add 0.5cm³ of lead acetate solution.
- A positive result is indicated by appearance of a black, or at least brown, color.
Test for Tyrosine with Phenol Reagent
- Folin-Ciocalteu reagent (phenol reagent) reacts with phenols in alkaline medium, resulting in an intense blue color.
- To 1cm³ of the protein solution add 1cm³ or 10% sodium carbonate.
- The test identifies proteins containing tyrosine
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