Protein Identification Tests

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Questions and Answers

What is the first step in the Biuret test procedure?

Fill the test tube with water

Shake the mixture well

Combine 1 ml sample with 1 ml 10% NaOH (correct)

Add a few drops of diluted CuSO4

What indicates a true coagulum in the Isoelectric Point (IEP) test?

No precipitate forms

A colored residue is formed

The opaque mass dissolves in water

The opaque mass does not dissolve (correct)

In the Fehling test, what color indicates that the reagent is ready for the sample?

Bright red

Colorless

Yellow

Dark clear blue (correct)

What is used to neutralize excess acid after hydrolysis in the Fehling after hydrolysis test?

Dilute NaOH (B) Signup and view all the answers

During the Heat coagulation test, how should the sample be prepared in the test tube?

Fill 3/4 with sample (D) Signup and view all the answers

What is the main function of the diluted CuSO4 in the Biuret using very diluted CuSO4 test?

To change the color of the solution (C) Signup and view all the answers

What is the total heating time in the Fehling test before adding the sample?

2-5 minutes (D) Signup and view all the answers

What is the purpose of adding lead acetate in the Sulfur test?

To react with sulfur and form a precipitate (B) Signup and view all the answers

What conclusion can be drawn if no violet color is observed in the Biuret test, but a violet ring appears in the Molisch’s test?

The sample is likely a carbohydrate. (C) Signup and view all the answers

What is indicated by a positive Biuret test after performing fusion with sodium hypobromide?

Presence of proteins. (B) Signup and view all the answers

If a sample turns blue when tested with red litmus paper, what does this suggest about the sample?

The sample is alkaline. (C) Signup and view all the answers

What color result is expected from the iodine test when starch is present?

Blue color. (A) Signup and view all the answers

What is the probable substance present if a red ppt is observed in Fehling’s test?

Reducing sugar. (B) Signup and view all the answers

If a sample exhibits no reddish-brown color in a ketose test, what does this suggest about the sample?

The sample is a monosaccharide. (A) Signup and view all the answers

In the scheme for identification of carbohydrates, what is associated with a violet color during the iodine test?

Dextrin. (D) Signup and view all the answers

What condition is indicated by no opaque mass in a heat coagulation test?

Non-protein nitrogen (NPN). (C) Signup and view all the answers

If a sample shows a positive result in both the Biuret test and Fehling’s test, which conclusion can be drawn?

The sample contains both proteins and reducing sugars. (A) Signup and view all the answers

Study Notes

Unknown Identification Scheme

Biuret Test: Violet color indicates protein; no violet color indicates carbohydrate or non-protein nitrogen (NPN).
Heat Coagulation Test: Opaque mass insoluble in dilute acetic acid indicates protein; no opaque mass indicates no protein.
Molisch's Test: Violet ring indicates carbohydrate; no violet ring indicates no carbohydrate.
Red Litmus Paper: Remains red indicates neutral protein; turns blue indicates alkaline protein.
Albumin Test: Red litmus paper remains red; turns blue when reacting with alkaline solutions.

Additional Tests

Sulfur Test: Used to differentiate proteins, with m-protein showing yellowish-brown color and casein showing a pale yellow color.
Peptone, Gelatin, and Casein Tests: Specific tests used to identify these different protein types. Peptone shows a pink color using a very dilute copper sulfate solution in half saturation. Gelatin reacts with a violet color under the same conditions.
Carbohydrate Tests: Uses iodine test to determine if a substance is dextrin or starch (blue color). Fehling's test determines reducing sugars by producing a red precipitate; sucrose gives no red precipitate. There are also specific tests (ketose test) to identify certain types of sugars.

Non-Protein Nitrogen (NPN) Tests

No violet color with Biuret Test & No violet ring with Molisch's test: Indicates NPN.
Red Litmus Paper: Remains red indicates NPN; turns blue indicates a specific NPN.
Further Tests: For NPN, different tests may be performed to further identify the specific NPN.

Chemical Reaction Procedures

Includes procedures for Molisch's test, Biuret test, iodine test, Fehling test, ketose test, and others. These procedures describe specific sample measurements (e.g., quantities of reagents, incubating times) and steps necessary to complete the specific test. This section also has procedures for heating/boiling, shaking, and adding reagents step-by-step.

Coagulation at Isoelectric Point (IEP)

Procedure: Using samples and acetic acid stepwise for precipitate formation (IEP). The procedure involves heating the precipitate to determine if it is a true or false coagulum (solubility).

Biuret test using diluted CuSO4

Procedure: Using diluted copper sulfate solution with a sample, followed by sodium hydroxide to identify specific substances through color changes.

Follin's Test

Procedure: Procedure for using Follin's reagent with a sample to detect various substances.

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Description

This quiz covers various tests used to identify proteins and carbohydrates, including the Biuret Test, Heat Coagulation Test, and others. Each test is designed to reveal specific characteristics of proteins, aiding in their differentiation. Test your knowledge on these biochemical identification methods.