E6 - COLOR REACTIONS OF AMINO ACIDS AND PROTEINS

Question 1

Complex, high molecular weight biomolecules composed of amino acids joined together by peptide bonds

Answer 1

Proteins

Question 2

How many a-amino acids are normally found in proteins?

Answer 2

Twenty (20)

Question 3

Reactions of proteins may be divided into three (3) categories, what are these?

Answer 3

The (3) three categories are reactions due to:
1. presence of specific chemical groups or linkages
2. acidity or basicity
3. colloidal nature
[Of the proteins]

Question 4

> Indicates the presence of peptide linkages
> Purplish to violet color due to cupric ions and 4 nitrogen ions
> All substances with 2 or more peptide bonds give the test and
> color produced is proportional to the number of peptide bonds present.

Answer 4

Biuret test

Question 5

> Amino acids react with ninhydrin (triketohydrindene hydrate) to yield CO2, NH3 (Ammonia), and aldehyde containing one less carbon than the amino acid
> Blue or purple color for colorimetric determination of amino acids

Answer 5

Ninhydrin test

Question 6

> Positive for proteins and amino acids containing an aromatic side chain
> Yellow

Answer 6

Xanthoproteic test

Question 7

What compound does not respond readily to the Xanthoproteic test?

Answer 7

Phenylalanine

Question 8

Phenylalanine requires what compound as a catalyst because of the absence of an activating group in the ring?

Answer 8

H2SO4 (Sulfuric Acid)

Question 9

> The phenolic group of tyrosine reacts with Millon-Nasse reagent (HgSO4 in H2SO4)
> Old rose or pink to red complex (upon heating)

Answer 9

Millon-Nasse test

Question 10

What is the complex of the phenolic compound in the Millon-Nasse test?

Answer 10

Mercury salt

Question 11

> Pyrrole ring of tryptophan undergoes halogenation with Br2 water in the presence of amyl alcohol
> Pink or lavender color in the alcohol layer

Answer 11

Bromine water test

Question 12

> A type of test that forms a brown-to-black precipitate of lead sulfide

Answer 12

Unoxidized sulfur test

Question 13

> Orange or red color with a-naphthol and sodium hypobromite

Answer 13

Sakaguchi reaction

Question 14

What are the materials needed for this experiment?

Answer 14

1% solution of egg albumin
1% casein
1% gelatin
0.1% solutions of tryptophan
0.1% solutions of ninhydrin
arginine
cysteine
tyrosine
saturated lead acetate
5% CuSO4 (Copper Sulfate)
10% & 20% of NaOH (Sodium Hydroxide)
Millon-Nasse reagent
Bromine water
Hopkins-Cole reagent
n-amyl alcohol
a-naphthol solution
distilled water
litmus paper

Question 15

What are the apparatus needed for this experiment?

Answer 15

Hot plate/stove
Alcohol lamp
600 mL beaker
50mL beaker
test tubes
test tube rack
10mL graduated cylinder
pipets
droppers
litmus paper
wire gauze

Question 16

results to: purplish to violet color

Answer 16

biuret test

Question 17

results to: blue or purple color

Answer 17

ninhydrin test

Question 18

results to: yellow color

Answer 18

xanthoproteic test

Question 19

results to: old rose or pink to red complex (color)

Answer 19

millon-nasse test

Question 20

results to: pink or lavender color

Answer 20

bromine water test

Question 21

results to: brown to black precipitate (of lead sulfide)

Answer 21

unoxidized sulfur test

Question 22

results to: orange and red color

Answer 22

sakaguchi reaction

Question 23

results to: violet or red-purple color

Answer 23

hopkins-cole test