Answered: 4. Classify proteins according to…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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COLOR REACTIONS OF PROTEINS Introduction: Protein is a polymer where its repeating unit are amino acids linked together by peptide linkage. There are 20 different amino acids classified according to their R groups or side chains. Side chains maybe acidic, basic, aliphatic straight chain, aliphatic branched chain, aromatic, OH containing, Sulfur containing, amide. The difference in their side chains determines their reaction to the different test for proteins and may identify the specific amino acids present in it. Proteins maybe classified according to their nutritional value. It may be complete, partially complete or incomplete protein depending on the presence or absence of essential amino acids. Objectives: At the end of the activity, the student can: 1. Identify specific amino acids based on their chemical group present. 2. Identify which sample is complete or incomplete protein. Reagents: 1 ml 10% NaOH, 3 drops 1% CuSO4, 10 drops 0.1% ninhydrin solution, 5 drops conc. HNO3, 5 drops millon’s reagent, 2 ml conc. H2SO4, 2 ml Hopkin’s-Cole reagent, 1 ml sulfanilic acid, 1 ml 0.5% NaNO2, 10% Na2CO3, 1 ml conc. NaOH, 10 drops 1% lead acetate, 15 drops bromine water, 1 ml n-amyl alcohol, 1 ml 20% NaOH, 10 drops alpha naphthol, conc. NH4OH, 10 ml 2% albumin, blue and red litmus paper, 10 ml 2% gelatin Materials: 10 Test tubes (20 ml), test tube rack, test tube brush, test tube holder, beaker, tripod,alcohol lamp, wire gauze, 10 ml graduated cylinder, dropper BRING: 2 marbles Procedure: Biuret Test – place 2 ml of albumin in a test tube. Add 1 ml of 10% NaOH, and then add drop by drop 1% CuSO4. Mix thoroughly after each addition. Note the color produced. Ninhydrin Test – to 2 ml of albumin, add 10 drops of 0.1% ninhydrin solution (freshly prepared). Cover with marble and heat in a boiling water bath for 1-2 minutes. Allow to cool and note the color produced. Xanthoproteic Test – to 2 ml of albumin, add 5 drops of conc. HNO3. Heat and note the color produced. Cool the solution and add excess conc. NH4OH until color changes to orange Millon’s Test – to 1 ml albumin, add 5 drops of millon’s reagent and boil in a water bath for a few minutes. Note color change. Hopkin’s-Cole Test – to 2 ml of albumin, add 1 ml Hopkin’s-cole reagent and mix. Incline the tube and slowly and carefully add 1 ml conc. H2SO4. Note the color of the ring produced. Lead Acetate Test – to 2 ml of albumin, add 1 ml conc. NaOHand10 drops of lead acetate and heat in boiling water for 10 minutes. Cool. Note the color produced. Pauly Test – mix 1 ml cold sulfanilic acid with 1 ml of 0.5% NaNO2. Cool in ice with constant shaking for 3 minutes. Add 2 ml of albumin and make it alkaline by placing red litmus paper then add 10% sodium carbonate until the red litmus paper changes to blue. Note color formed. Bromine Water – mix 1 ml of albumin with 10 drops of freshly prepared bromine water. Shake with 1 ml n-amyl alcohol and observe the color of the alcohol layer. Sakaguchi Test – mix 1 ml of 20% NaOH with 2 ml of albumin and add 10 drops of alpha naphthol. Mix thoroughly and add 5 drops of freshly prepared bromine water. Note color formed. ***REPEAT PROCEDURES 1-9 USING GELATIN INSTEAD OF ALBUMIN