Xanthoproteic Test Practical Experiment
Summary
TLDRThe video explains the xanthoproteic test, a biochemical method used to detect aromatic amino acids like tyrosine, tryptophan, and phenylalanine in proteins. The test involves treating samples with concentrated nitric acid, which turns yellow upon reaction with aromatic groups. Adding a basic solution like sodium hydroxide or ammonia deepens the color to orange. Proteins like egg albumin and casein show positive reactions due to their aromatic amino acid content. Phenylalanine reacts weakly and only after extended heating. The video demonstrates the test procedure and highlights its results with various samples.
Takeaways
- đ§Ș Xanthoprotic test is a qualitative biochemical test used to detect and differentiate aromatic amino acids such as phenylalanine, tyrosine, and tryptophan.
- đ The test is named after 'xanthoproteic acid,' a yellow substance formed when aromatic amino acids react with concentrated nitric acid.
- đŹ Aromatic amino acids are nitrated by heating with concentrated nitric acid, producing yellow-colored nitro derivatives.
- âïž The yellow xanthoproteic acid turns deep orange when a basic or alkaline solution like ammonia or sodium hydroxide is added.
- 𧫠The xanthoprotic test is used to detect proteins containing aromatic amino acid units.
- đ§Ș Phenylalanine gives a weak positive reaction only after extended heating due to the stability of its phenyl group.
- đ The experiment uses tyrosine, tryptophan, phenylalanine, glutamine (a non-aromatic amino acid), egg albumin, casein, and distilled water as samples.
- âïž After heating with nitric acid, the aromatic amino acids and proteins (like egg albumin and casein) turn yellow, indicating a positive reaction.
- đĄïž After adding alkali, the yellow color turns orange or brownish, confirming the presence of aromatic amino acids.
- đ§Ș Non-aromatic amino acids and the control sample do not show any significant color changes, indicating a negative reaction.
Q & A
What is the purpose of the xanthoproteic test?
-The xanthoproteic test is a qualitative biochemical test used to detect and differentiate aromatic amino acids, such as phenylalanine, tyrosine, and tryptophan, from non-aromatic amino acids. It also helps identify the presence of proteins containing these aromatic amino acid units.
Why is the test named 'xanthoproteic'?
-The test is called 'xanthoproteic' because it leads to the formation of a yellow substance known as xanthoproteic acid, which results from the reaction of aromatic amino acids or proteins with concentrated nitric acid.
What principle does the xanthoproteic test rely on?
-The xanthoproteic test is based on the principle that aromatic groups in amino acids or proteins are nitrated by heating with concentrated nitric acid, producing yellow nitro derivatives known as xanthoproteic acid.
What happens when an alkaline solution is added after nitration in the xanthoproteic test?
-When an alkali, such as sodium hydroxide or ammonium hydroxide, is added, the xanthoproteic acid turns orange due to the formation of a salt of the nitrated compound.
Why does phenylalanine give a weak reaction in the xanthoproteic test?
-Phenylalanine gives a weak positive reaction because the phenyl group is stable and doesnât react easily with nitric acid under normal conditions. A faint yellow color may appear after extended heating.
What changes can be observed after adding concentrated nitric acid to aromatic amino acids?
-After adding concentrated nitric acid and heating, the test tubes containing aromatic amino acids like tyrosine, tryptophan, and proteins with aromatic units such as egg albumin and casein will turn yellow.
What color change occurs after adding an alkaline solution in the xanthoproteic test?
-After adding an alkaline solution, the yellow color from the nitrated aromatic amino acids turns orange or brownish, indicating a positive xanthoproteic reaction.
How can the presence of aromatic amino acids in proteins be confirmed using the xanthoproteic test?
-Proteins such as egg albumin and casein, which contain aromatic amino acids, show a positive xanthoproteic reaction by turning yellow or orange after nitration and the addition of alkali, confirming the presence of aromatic amino acids.
Why is there no color change in the control tube with distilled water?
-The control tube with distilled water does not contain any aromatic amino acids or proteins, so no color change occurs, indicating a negative xanthoproteic reaction.
What are the main reagents used in the xanthoproteic test?
-The main reagents used in the xanthoproteic test are concentrated nitric acid, which nitrates the aromatic amino acids, and sodium hydroxide or ammonium hydroxide, which induces the color change by forming a salt of the nitro compound.
Outlines
đ§Ș Overview of the Xanthoproteic Test
The Xanthoproteic test is a qualitative biochemical test used to detect and differentiate aromatic amino acids containing phenolic or indolic groups, such as phenylalanine, tyrosine, and tryptophan, from non-aromatic amino acids. It is also used to identify proteins with these aromatic amino acid units. The test produces a yellow substance, xanthoprotic acid, which turns deep orange upon adding an alkaline solution. Aromatic amino acids undergo nitration when treated with concentrated nitric acid, yielding nitro derivatives called xanthoprotic acid. Phenylalanine gives a weak reaction due to the stability of its phenyl group, reacting only after extended heating. The video demonstrates both positive and negative reactions using samples of aromatic amino acids, non-aromatic amino acids, and proteins.
đŹ Xanthoproteic Test Procedure
This section describes the procedure for conducting the Xanthoproteic test. Seven labeled test tubes are filled with different samples, including aromatic amino acids (tyrosine, tryptophan, phenylalanine), non-aromatic amino acids (glutamine), proteins (egg albumin, casein), and distilled water (control). One ml of concentrated nitric acid is added to each tube, and the mixture is heated in a boiling water bath. Aromatic amino acids and proteins containing aromatic units turn yellow, indicating a positive result. Upon cooling and adding sodium hydroxide or ammonium hydroxide, the yellow color deepens to orange or brownish in the positive samples. Egg albumin and casein show this reaction, indicating the presence of aromatic amino acids in their structure.
𧏠Negative Reactions and Phenylalanine's Unique Behavior
This part highlights the lack of significant color changes in the control and non-aromatic amino acid samples, which confirms a negative Xanthoproteic reaction. Phenylalanine, despite being aromatic, shows a delayed and weak reaction due to its stable phenyl group. The yellowish color in phenylalanine's test tube only appears after prolonged heating and an increased concentration of nitric acid. This delayed positive result emphasizes the unique reactivity of phenylalanine compared to other aromatic amino acids. The experiment effectively demonstrates both the positive reaction of aromatic amino acids and the slower, weaker response of phenylalanine.
đ„ Conclusion and Additional Resources
The video concludes by summarizing the Xanthoproteic test's role in identifying aromatic amino acids and proteins with these amino acid units. The unique behavior of phenylalanine is revisited, and viewers are encouraged to explore more biochemical tests by clicking on end screen links or checking the video description for additional resources. This wrap-up encourages further learning on related biochemical topics.
Mindmap
Keywords
đĄXanthoprotic test
đĄAromatic amino acids
đĄNitric acid
đĄXanthoprotic acid
đĄAlkaline solution
đĄPhenylalanine
Highlights
Xanthoprotic test is used to detect and differentiate aromatic amino acids containing phenolic or indolic groups such as phenylalanine, tyrosine, and tryptophan.
The test detects proteins with aromatic amino acids in their structure.
The yellow substance formed during the test is called xanthoprotic acid.
Xanthoprotic acid is a non-crystallizable yellow substance derived from proteins and aromatic amino acids upon treatment with concentrated nitric acid.
The yellow nitrated product turns deep orange when a basic solution like ammonia or hydroxide is added.
The test is based on the principle that aromatic groups in amino acids or proteins are nitrated by heating with concentrated nitric acid to form yellow nitro derivatives.
Phenylalanine gives a weak positive reaction due to the stability of its phenyl group, reacting only after extended heating.
The test can differentiate between aromatic amino acids and non-aromatic amino acids based on color changes.
Positive reactions show a color change from yellow to orange, particularly with tyrosine, tryptophan, and proteins like egg albumin and casein.
Casein and egg albumin proteins show a faint yellow color, indicating the presence of aromatic amino acids.
Non-aromatic amino acids do not show significant color changes, indicating a negative xanthoprotic reaction.
Phenylalanine may show a faint yellow color after extended exposure to concentrated nitric acid and alkali.
The experiment demonstrates delayed but positive reactions in phenylalanine due to the stability of its phenyl group.
The experiment helps distinguish between aromatic and non-aromatic amino acids through visible color changes.
The yellow to orange color change in casein and egg albumin shows that these proteins contain aromatic amino acids.
Transcripts
xanthoprotic test is a qualitative
biochemical test to detect and
differentiate aromatic amino acids
containing phenolic or indolic groups
such as phenylalanine tyrosine and
tryptophan from other non-aromatic amino
acids
it is also used to detect the presence
of proteins containing such aromatic
amino acid units in their structure
the test is named xanthoprotege due to
the formation of a yellow substance
called xanthoprotic acid
during the test
xanthoprotic acid is a
non-crystallizable yellow substance
derived from proteins and aromatic amino
acids upon the treatment with
concentrated nitric acid this yellow
nitrated product then turns deep orange
with the addition of a basic or alkaline
solution such as ammonia or a hydroxide
the xanthoprotea test is a based on the
principle that aromatic groups in the
amino acids or proteins are nitrated by
heating with concentrated nitric acid to
yield yellow colored nitro derivatives
called xanthoprotic acid
upon the addition of an alkali however
the xanthoproteate acid turns orange due
to the formation of a salt of this nitro
compound
the aromatic amino acid phenylalanine
gives a weak positive reaction only
after an extended period of heating
because the phenyl group in
phenylalanine is quite stable and
doesn't react with nitric acid under
normal conditions
in this video we'll demonstrate positive
and negative xanthoprotein tests using
samples of aromatic amino acid
non-aromatic amino acid and a protein
with aromatic amino acid units to
perform this test we'll need the
following
test samples consisting of one percent
solutions each of tyrosine tryptophan
phenylalanine glutamine or any other
non-aromatic amino acid
egg albumin
casein or any other protein containing
aromatic amino acids and distilled water
is controlled sample
concentrated nitric acid 40 sodium
hydroxide or ammonium hydroxide solution
seven clean dry identical test tubes
nine graduated droppers or pipettes of
one or two ml capacities test tube stand
test tube holder
to begin the test take the seven
appropriately labeled test tubes in the
test tube stand using seven different
droppers or pipettes add one ml each of
the five test samples including the
distilled water the tube containing the
distilled water will serve as the
negative control for this experiment
now using a separate dropper or pipette
add one ml each of concentrated nitric
acid to all the seven tubes mix the
tubes well by gently swirling them
the tube containing the protein solution
such as egg albumin might develop a
white or cloudy precipitate due to the
denaturation of the protein by the acid
place the tubes in boiling water bath
for about 30 seconds to a minute observe
the change in color if any in the seven
tubes you'll notice that the tube
containing the aromatic amino acids
tyrosine tryptophan and the tube
containing the egg albumin and casein
immediately turns yellow after the
addition of the nitric acid and heating
in the water bath
remove the tubes and cool them under
running tap water or by immersing them
in ice cold water
now add 1 or 2 ml each of 40 sodium
hydroxide or ammonium hydroxide solution
to the tubes mix well and observe for
color change if any in the tubes
again the tubes containing the tyrosine
tryptophan
the egg albumin and casein will turn
yellow
to orange or brownish in color the tube
containing the casein solution also
shows a very faint yellowish color this
implies that egg albumin as well as
casein are two such proteins that
contain some amount of aromatic amino
acids in their structure
both colors are considered positive
xanthoprotic reaction
the rest of the tubes including the
control tube do not show any significant
color changes throughout the test
whether yellow or orange this is a
negative xanthoprotique reaction in the
case of the test tube containing
phenylalanine if the concentration of
the sample is increased and kept in the
water bath and allowed to react with the
nitric acid for a prolonged period of
time it might show a faint yellowish
color on addition of the alkali solution
this experiment using different test
samples clearly demonstrates the
positive
reaction shown by aromatic amino acids
and proteins containing aromatic amino
acid units it also demonstrates the
delayed but positive reaction shown by
phenylalanine which has a very stable
phenyl group as previously explained at
the start of this video
this is all about the xanthoprotein test
for aromatic amino acids make sure to
watch my other biochemical test videos
as well by clicking on the end screen
card shown on the screen right now or
the various links given in the
description below thanks for watching
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