Lesson 6 : Proteins Flashcards
Proteins (_____________) are that are _____________ made up of ________________ arranged in a _______________.
Polypeptides
biochemical compounds
amino acids
linear chain
The amino acids in a polymer are joined together by the _____________ between the ____________ and the amino group of ___________________.
peptide bonds
carboxyl group
adjoining amino acids
Structures of Proteins
Primary
Secondary
Tertiary
Quaternary
What are Amino Acids
the monomer units of proteins, are molecules containing an amino group, a carboxyl group and a side chain.
Amino acids can be differentiated by their ___________________.
variations in their side chains
In amino acids, the carboxyl group is _______________ charged, and the amino group is _____________ charged. Amino acids are classified based on their charges. At a particular pH, amino acids have ____________ charge. This pH is known as the _______________. When amino acids have no overall charge, they are known as _______________.
negatively
positively
no overall
isoelectric point
zwitterions
Amino acids are vital to human existence. They serve as ____________________ and as ____________________.
building blocks of proteins
intermediates in metabolism
Purpose of Qualitative Tests for Proteins
Biuret Test
Ninhydrin Test
Xanthoproteic Test
Millon’s Test
Sakaguchi Test
Hopkins-Cole Test
Lead Acetate Test
Biuret Test : identifies the presence of proteins and peptide bonds
Ninhydrin Test : used to check whether a given analyte contains amines or a-amino acids.
Xanthoproteic Test : determine the amount of protein soluble in a solution, using Nitric acid.
Millon’s Test : presence of phenol-containing protein
Sakaguchi Test : detect presence of arginine or a guanidinium compound in proteins
Hopkins-Cole Test : indole ring containing amino acid in proteins; tryptophan-containing proteins
Lead Acetate Test : used to detect sulfur-containing amino acids (cystine or cysteine)
Biurets Test Procedure
- Add 1 mL of 10% NaOH to 3 ml of each of the protein suspensions (albumin, casein, gelatin - in 3 separate test tubes), and mix.
- Add a drop of 0.01 M of CuSO4, to each and mix if no definite color develops, add another drop or two of the CuSO4 solution.
Ninhydrin Test Procedure
- Add 5 drops of 0.1% Ninhydrin solution to 2 mL each of the 3 protein suspensions.
- Heat in boiling water for 10 minutes. Observe and record the results.
Xanthoproteic Test Procedure
- Slowly add 1 mL of concentrated HNO3 to 3 mL of each of the protein suspensions.
- Place in water bath for about 30 seconds and place each test tube in a rack to cool the solutions.
- Add slowly, drop by drop, saturated NaOH to each test tube until the solutions are alkaline (or basic)
Millon’s Test Procedure
- Add 5 drops of fresh Millon’s reagent to 3 mL of each protein suspension.
- Carefully heat each mixture in boiling water for 5 minutes.
- Cool the test tubes and note the colors formed.
Sakaguchi Test Procedure
- Add 1 mL of 10% NaOH and 1mL of 0.02% alphanaphthol solution to 3mL of **each of the protein suspensions. **
- After** 3 minutes,** add **2-4 mL of bromine water to each. A strong red color can be stabilized by adding urea **to destroy the excess hypobromite.
Hopkins-Cole Test Procedure
- Add 2 mL of Hopkins-Cole reagent to 3 mL of each of the 3 protein suspensions.
- Mix. Incline each test tube and with a dropper, add slowly about 1 mL conc. H2SO4 down the side of the tube so that two layers will form. Do not stir.
- Let stand for 1 to 2 minutes and note the color formed in-between the layers.
Lead Acetate Test Procedure
- Add 5 mL of 5% NaOH and a few crystals of Pb(Ac)2 (lead (II) acetate) to 3 mL of each protein suspension.
- Heat in boiling water for 5-10 minutes with occasional mixing of the contents of the tube. Describe the color change.
The Biuret test (also known as _____________) positively identifies the presence of ____________ and ___________. The reaction in this test involves the complex formation of the ___________________ in a _______________.
Piotrowski’s test
proteins
peptide bonds
proteins with Cu2+ ions
strongly alkaline solution
Despite the name of the test, the reagent used to perform the procedure does not contain Biuret, a chemical derived from _______. It is named so because it also gives a positive reaction to the ___________ in the Biuret molecule.
Urea
peptide-like bonds
Biuret test Expected Reaction
POSITIVE: Purple colored solution
NEGATIVE: Blue colored solution
Ninhydrin Test Expected Reaction
For ammonia, primary/secondary amines, and amino acids, deep purple colour is obtained.
For hydroxyproline and proline, a yellow colour is obtained.
For asparagine, brown colour is obtained.
If no colour change is observed, the analyte does not contain amino acids, amines, or ammonia.
The ninhydrin test is a chemical test which is used to check whether a given analyte contains ___________ or ____________.
amines or a-amino acids
In this test, ninhydrin (a chemical compound with the formula ____________; IUPAC name: ____________) is added to a test solution of the analyte.
C9H604
2,2-dihydroxyindane-1,3-dione
In the ninhydrin test, the development of a ___________color indicates the presence of _____________, _________________, or ________________ in the analyte.
deep blue
ammonia
primary/secondary amines
amino acids
Xanthoproteic test is a _________________ to determine the ____________________ in a solution, using ______________.
qualitative test
amount of protein soluble
Nitric acid
The test is named after the ____________ substance produced after the reaction - Xanthoproteic acid.
yellow color
Xanthoproteic Test Expected Reaction
POSITIVE: Formation of yellow to orange color
NEGATIVE: No color change
In Millons test, if too much reagent is used, the color may ________________
disappear in boiling
Millon’s test is specific to ____________ containing structures. Millon’s reagent is ______________, in which ____________ is dissolved. As a result of the reaction a _______________ or a _____________ is considered a ___________ test. A ___________ precipitate of is not a positive reaction but usually indicates that the solution is _____________.
phenol
concentrated HNO3
mercury
red precipitate
red solution
positive
yellow
Mercuric (II) oxide (HgO)
too alkaline
Who developed the Millons Test
The test was developed by a French chemist, Auguste Nicolas Eugene Millon
Millons Test Expected Reaction
POSITIVE: Brick red colored solution or red precipitate
NEGATIVE: No red color
Sakaguchi Test Expected Reaction
Positive result: Formation of red color. This indicates the presence of an arginine or guanidinium compound.
Negative result: Absence of red color. This indicates an absence of arginine or a guanidinium compound.
Sakaguchi test is based on the principle of reaction between _____________ and the ________________ in ___________, in the presence of an _______________. The exact mechanism of the reaction is not yet known; however, the reaction results in the formation of a ______________ due to the formation of an ____________structure
1-naphthol
guanidinium groups
arginine
oxidizing agent
red-colored complex
indole-like
Lead sulfide test (or Lead acetate test) is a biochemical test for the detection of amino acids like ______________ and _______________. The test is a specific test for the detection of amino acids containing ________,_________ in __________, and ______________ in __________. The test is also called a lead acetate test as the reagent for the test is lead acetate. Even though the test is specific for the detection of sulfur-containing amino acids, ___________ doesn’t give a positive result in this test.
cysteine and cystine
sulfur, S-S group ; cysteine
S-H group in cysteine
methionine
Hopkin-Cole’s test is a chemical test for the determination of the presence of _______________ of ___________________.
heterocyclic side chain (indole group)
tryptophan in proteins
Hopkins-Cole test Expected Reaction
POSITIVE: Purple color ring at the interface
NEGATIVE: No formation of purple color ring
The Hopkins-Cole test is named after ____________ and ___________ for their work on ________________.
Frederick Gowland Hopkins and Sydney W. Cole
tryptophan isolation
Lead Acetate Expected Reaction
Positive test: Formation of black precipitate at the bottom of the test tube. This indicates the presence of cysteine or cystine in the solution.
Negative test: Absence of black residue in the test tube. This indicates the absence of cysteine or cystine.
