Qualitative Tests for Proteins

Summary

This video script details a series of qualitative tests to explore the properties of amino acids and proteins using casein, albumin, and gelatin. It covers the Biuret test for peptide bonds, the Ninhydrin test for alpha-amino groups, the Xanthoproteic test for tyrosine and tryptophan, the Biuret test for tyrosine, the Sakaguchi test for arginine, the Hopkins-Cole test for tryptophan, and the Lead acetate test for cysteine. Each test is described with its procedure and expected color changes, offering a comprehensive guide to protein analysis.

Takeaways

• 🧪 The experiment involves observing properties of amino acids and proteins using qualitative tests.
• 🔍 Three types of proteins are used: casein, albumin, and gelatin.
• 🔬 The first test is the Biuret test, which detects the presence of peptide bonds in proteins.
• 💧 The procedure involves adding sodium hydroxide and copper sulfate to each protein sample and observing the color change.
• 🔥 The second test is the Ninhydrin test, used to detect alpha-amino groups in proteins or free amino acids, producing a blue or purple color upon heating.
• 🌡️ The Xanthoproteic test identifies the presence of tyrosine and tryptophan by nitration, causing a color change when reacted with concentrated nitric acid at high temperature.
• 🍅 The Millon's test is specific for tyrosine, giving a red color or precipitate in the presence of this amino acid.
• 🚰 The Sakaguchi test detects arginine or arginine residues, resulting in a red-colored complex.
• 🌈 The Hopkins-Cole test is for tryptophan, indicated by a violet color between two layers when a positive test occurs.
• 💎 The lead acetate test, also known as the sulfur reaction test, is used to detect cysteine, with a black or gray precipitate indicating a positive result.

Q & A

What is the purpose of the qualitative tests in the script?

The purpose of the qualitative tests is to observe and detect specific properties of amino acids and proteins, such as the presence of peptide bonds, alpha amino groups, and certain amino acids like tyrosine, tryptophan, arginine, and cysteine.

What are the three proteins used in the experiment mentioned in the script?

The three proteins used in the experiment are casein, albumin, and gelatin.

What is the Buret test and what does it detect?

The Buret test is a general qualitative test used to detect the presence of peptide bonds that connect amino acids to form proteins.

What chemicals are used in the Buret test and what is the procedure?

In the Buret test, 1 ml of 10% sodium hydroxide solution is added to each protein sample, mixed, and then one to three drops of 0.01 M copper sulfate are added until a definite color is produced.

What is the Ninhydrin test and what does it indicate?

The Ninhydrin test is a qualitative test used to detect the presence of alpha amino groups of proteins or free amino acids, which gives a blue or purple colored complex.

How is the Ninhydrin test performed according to the script?

The Ninhydrin test involves adding 5 drops of 0.1% ninhydrin solution to each protein sample and then heating the samples in a boiling water bath for 10 minutes. The color produced is then noted.

What is the Xanthoproteic test and what does it detect?

The Xanthoproteic test is used to detect the presence of the amino acids tyrosine and tryptophan. When these amino acids react with concentrated nitric acid at high temperature, a color change occurs.

How does the color change in the Xanthoproteic test indicate the presence of tyrosine and tryptophan?

The benzene ring in tyrosine and tryptophan becomes nitrated when reacting with concentrated nitric acid, causing a color change that indicates the presence of these amino acids.

What is the Biuret test and what color does it produce when tyrosine is present?

The Biuret test is for tyrosine and proteins containing tyrosine, which will give a red color or precipitate when present.

What is the Sakaguchi test and what does it detect?

The Sakaguchi test is for the presence of arginine or arginine residues, which gives a red colored complex.

What is the Hopkins-Cole test and what does it indicate?

The Hopkins-Cole test is used to detect the presence of tryptophan in proteins. A violet color between two layers indicates a positive test.

What is the Sulfur reaction or Lead acetate test and what does it indicate?

The Sulfur reaction or Lead acetate test is for the presence of cysteine or proteins containing this amino acid. A black or gray precipitate indicates a positive test.

Outlines

00:00

🧪 Amino Acid and Protein Qualitative Tests

This paragraph introduces a series of qualitative tests to observe the properties of amino acids and proteins. The experiment utilizes three proteins: casein, albumin, and gelatin. The first test mentioned is the Buret test, which detects peptide bonds connecting amino acids in proteins. The procedure involves adding sodium hydroxide solution to the protein samples and then copper sulfate to produce a color change. The second test is the Ninhydrin test, which detects alpha-amino groups in proteins or free amino acids, resulting in a blue or purple color. This test requires heating the protein samples with ninhydrin solution in a boiling water bath. The third test is the Xanthoproteic test, used for detecting tyrosine and tryptophan amino acids, which react with concentrated nitric acid to change color. The procedure includes adding nitric acid, heating, and then neutralizing with sodium hydroxide. The paragraph concludes with the mention of Milan's test, which also detects tyrosine and results in a red color or precipitate.

05:02

🌡️ Additional Qualitative Tests for Proteins

This paragraph continues the discussion on qualitative tests for proteins, focusing on specific amino acids. Milan's test is described in more detail, involving the addition of fresh melon's reagent and heating in a boiling water bath, with the results observed after cooling. The Sahaguchi test is introduced for detecting arginine, where a red complex is formed upon the addition of sodium hydroxide, alpha-naphthol, and bromine water. The Hopkins-Cole test is mentioned for detecting tryptophan, where a violet color between two layers indicates a positive result. This test involves adding Hopkins-Cole reagent and concentrated sulfuric acid to the protein suspensions. Lastly, the Sulfur Reaction or Lead Acetate test is described for detecting cysteine, where a black or gray precipitate indicates a positive test. The procedure includes adding sodium hydroxide solution and lead acetate crystals, followed by heating and cooling.

Keywords

💡Amino Acids

Amino acids are the building blocks of proteins, each with a unique side chain that determines its properties. They are essential for various biological functions, including the structure, function, and regulation of the body's tissues and enzymes. In the video, amino acids are the focus of the qualitative tests to understand the properties of proteins, such as through the formation of peptide bonds.

💡Proteins

Proteins are large, complex molecules that play many critical roles in the body, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules from one location to another. The video script describes an experiment observing the properties of proteins, such as casein, albumin, and gelatin, through various qualitative tests.

💡Qualitative Test

A qualitative test is a type of analytical procedure used to provide information about the presence or absence of a particular substance or property within a sample. In the context of the video, several qualitative tests are conducted to detect specific properties of proteins, such as the presence of peptide bonds or amino groups.

💡Peptide Bonds

Peptide bonds are covalent chemical bonds that link amino acids together in a protein chain. They are formed through a dehydration synthesis reaction between the amino group of one amino acid and the carboxyl group of another. The script describes a test to detect these bonds, which is crucial for understanding the structure of proteins.

💡Sodium Hydroxide

Sodium hydroxide, also known as lye or caustic soda, is a strong base used in various industries. In the script, it is used in the Buret test to interact with protein samples, facilitating the detection of peptide bonds through a color change reaction with copper sulfate.

💡Copper Sulfate

Copper sulfate is a chemical compound that can act as a reagent in certain chemical tests. In the video, it is used in conjunction with sodium hydroxide to identify the presence of peptide bonds in protein samples, as it produces a distinct color when it reacts with them.

💡Ninhydrin Test

The ninhydrin test is a specific qualitative test used to detect the presence of alpha-amino groups in proteins or free amino acids, resulting in a blue or purple color complex. The script outlines this procedure, emphasizing its use in identifying protein samples.

💡Tyrosine

Tyrosine is an amino acid with a four-letter code TYR and is one of the 20 standard amino acids. It contains a phenol side chain and is important for the function of several proteins. The script mentions a test for tyrosine, indicating its presence by a color change when proteins react with concentrated nitric acid.

💡Tryptophan

Tryptophan is an essential amino acid that plays a significant role in many biological functions, including the production of serotonin, a neurotransmitter. The script describes a test to detect tryptophan in proteins, which involves a reaction with Hopkins reagent, resulting in a violet color between two layers.

💡Arginine

Arginine is a semi-essential amino acid that is important for伤口 healing, immune function, and the urea cycle. The script describes the Sakaguchi test, which is used to detect the presence of arginine or arginine residues in proteins, indicated by a red-colored complex.

💡Cysteine

Cysteine is an amino acid that contains sulfur and is known for its antioxidant properties. It plays a role in the structure of proteins by forming disulfide bonds. The script mentions a test for cysteine, where the presence of this amino acid in proteins is indicated by a black or gray precipitate after a reaction with lead acetate.

💡Lead Acetate

Lead acetate is a chemical compound that can be used as a test reagent for the presence of certain substances. In the context of the video, it is used in the sulfur reaction or lead acetate test to identify proteins containing cysteine, as it forms a precipitate upon reaction.

Highlights

Observing properties of amino acids and proteins through qualitative tests.

Using three proteins: casein, albumin, and gelatin.

Buret test to detect peptide bonds connecting amino acids.

Procedure involves adding sodium hydroxide solution and copper sulfate.

Ninhydrin test for detecting alpha amino groups in proteins.

Ninhydrin test results in a blue or purple colored complex.

Sensor protic test for tyrosine and tryptophan amino acids.

Benzene ring nitration in tyrosine and tryptophan changes color.

Milan's test for tyrosine with a red color or precipitate.

Sahaguchi test for arginine residue with a red colored complex.

Hopkins coal test for tryptophan indicating a violet color.

Sulfur reaction or lead acetate test for cysteine.

Black or gray precipitate in the sulfur reaction indicates cysteine.

Detailed procedure for each test including reagents and conditions.

Qualitative tests provide insights into the composition and structure of proteins.

Color changes in tests are indicative of specific amino acids.

Experimental setup and procedure are crucial for accurate results.

Observations and results are key to understanding protein properties.

Transcripts

for today's activity

we will be observing some of the

properties of amino acids and proteins

through a qualitative test

and for this experiment we will be using

three proteins

casein albumin and gelatin

our first qualitative test is buret test

a general test used to detect the

presence of peptide bonds

which connect amino acids forming

proteins

and the procedures for this experiment

is as follows

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now that we have our setup ready we can

now start the test

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we start off by adding 1 ml of 10

percent sodium hydroxide solution

into each of the protein sample and then

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mix

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then add one to three drops of 0.01

molars of copper sulfate

or until a definite color is produced

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do

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our second qualitative test is called

ninhydrin test

and the procedures for this experiment

are as follows

ninhydrin test is a qualitative test

used to detect the presence of alpha

amino groups of proteins

or free amino acids giving a blue or

purple colored

complex first we will be adding 5

drops of 0.1 percent nin hydrogen

solution

to each of our protein samples and then

we will heat this in boiling water bath

for 10

minutes after that take note of the

color that will be produced

this is the result and the color

produced after the solutions are taken

out of the water bath

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sensor protic test is a test used to

detect the presence of the amino acids

tyrosine and tryptophan when proteins

containing this two amino acids react

with concentrated nitric acid at high

temperature

the benzene ring in tyrosine and

tryptophan becomes nitrated

causing a change in color

in this test one ml of concentrated

nitric acid

is added to each protein sample and then

it will be placed in a water bath for

30 seconds after it has cooled down

saturated sodium hydroxide solution

was slowly added drop by drop until the

solutions are alkaline

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and these are the results after the

addition of saturated sodium hydroxide

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milan's test is a test for tyrosine and

proteins containing tyrosine

which will give a red color or

precipitate when present

here we will add five drops of fresh

melons reagent

into each of the protein solutions and

then they will be heated in a boiling

water bath for five minutes

after the solutions were cooled down

this are the results

next is the sahaguchi test it is a test

for the presence of

arginine or arginine residue giving a

red colored complex

for this test 1 ml of 10 percent sodium

hydroxide

and 1 ml of 0.02 alpha naphthol

were added to each of the protein

solution

and then we waited for 3 minutes before

adding 2 to 4 ml of bromine water

upon the addition of bromine water a

change in color

in the solution will be observed

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so

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hopkins coal is a test used to detect

the presence of tryptophan in the

protein

a violet color in between two layers

indicate a positive test

in here we will be adding 2ml of hopkins

coal reagent to each of the protein

suspensions

and then while the test tube is inclined

about one ml of concentrated sulfuric

acid

will be added slowly and then it will be

allowed to stand for about one to two

minutes

and note the color formed in between the

two layers

a positive test is indicated by the

formation of a violet

ring in between two layers but for this

test

take note of the colour of the ring that

was produced

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for our last test we have the sulfur

reaction or the lead acetate test

this is a test for the presence of

cysteine or proteins containing these

amino acids

a black or gray precipitate indicates a

positive test

this test about 5 ml of 5 percent sodium

hydroxide solution was added to each

protein suspension

and then a few crystals of lead 2

acetate was also added

it was then heated in boiling water for

5 to 10 minutes with occasional mixing

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after the solutions were taken out of

the water bath and allowed to cool down

this are the results

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do

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you