MIDTERM: COLOR REACTIONS

Question 1

what are the 3 reactions of proteins

Answer 1

colloidal nature of proteins
acidity and basicity of protein
presence of specific chemical groups

Question 2

this test is given by free amino acids, small peptides, and protein will react

Answer 2

ninhydrin reaction

Question 3

ninhydrin reacts with amino acids to form hydrindantin and then it further forms __ by reacting with ammonia and another ninhydrin

Answer 3

ruhemann’s purple

Question 4

in alkaline medium copper from CuSO4 will form a coordination complex with the peptide bond ; compounds that contain two or more peptide bonds will react with Cu2+ in a basic solution

Answer 4

biuret test

Question 5

what is the positive indication of ninhydrin reaction

Answer 5

purple color or blue-purple color

Question 6

what is the positive indication of biuret test

Answer 6

violet pink complex

Question 7

aromatic amino acids such as phenylalanine, tyrosine, and tryptophan respond to this test

Answer 7

xanthoproteic test

Question 8

in xanthoproteic test, what gives a weak positive reaction

Answer 8

phenylalanine

Question 9

what is the positive indication of xanthoproteic test

Answer 9

orange-yellow color

Question 10

In the presence of concentrated nitric acid, the aromatic phenyl ring is nitrated to give __ colored nitro derivatives.

Answer 10

yellow

Question 11

At alkaline pH, the color changes to __ due to the ionization of the phenolic group.

Answer 11

orange

Question 12

Specific to phenolic group of tyrosine. The hydroxy benzene group of tyrosine reacts with Millon’s reagent

Answer 12

millon-nasse test

Question 13

what is a positive indication of the millon-nasse test

Answer 13

red color or old rose

Question 14

The test indicates presence of indole group containing amino acid.

Answer 14

hopkins-cole reaction

Question 15

what is a positive indication of the hopkins-cole reaction

Answer 15

violet colored ring

Question 16

Test for presence of free Tryptophan

Answer 16

bromine water test

Question 17

what is a positive indication of the bromine water test

Answer 17

pinkish lavender or violet color in the alcohol layer

Question 18

This test is specific for the detection of Tyrosine or Histidine.

Answer 18

pauly reaction

Question 19

The reagent used for this test contains__ dissolved in hydrochloric acid.

Answer 19

sulphanilic acid

Question 20

Sulphanilic acid upon diazotization in the presence of sodium nitrite and hydrochloric acid results in the formation a

Answer 20

diazonium salt

Question 21

what is a positive indication of the pauly reaction

Answer 21

red colored chromogen (azo dye)

Question 22

When a protein solution is boiled with an alkali, the sulfur of cysteine and cystine splits to form sodium sulfide.

Answer 22

lead acetate reaction

Question 23

in lead acetate reaction, test is not answered by __ because the sulphur is involved in a ___ linkage.

Answer 23

methionine ; thioether

Question 24

what is a positive indication of the lead acetate reaction

Answer 24

black lead sulfide

Question 25

Under alkaline condition, α naphthol (1 hydroxy naphthalene) reacts with a mono substituted guanidine compound like arginine

Answer 25

sakaguchi reaction

Question 26

what is a positive indication of a sakaguchi reaction

Answer 26

red color

Question 27

what are the different tests and reaction under color reactions of proteins and amino acids

Answer 27

ninhydrin reaction
biuret test
xanthoproteic test
millon-nasse test
hopkins-cole reaction
bromine water test
pauly reaction
lead acetate reaction
sakaguchi reaction

Question 28

a blank test will always give a __ result

Answer 28

negative