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Quantitative Tests For Amino Acids And Proteins Biology

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    The intent is, finding whether aminic acids or proteins are present in solution and amino acids are transporting a free aminoalkane group by utilizing biuret trial, ninhydrin trial, xanthoproteic trial and heavy metal precipitation trial.


    Proteins are organic compounds made of amino acids.The amino acids joined together by the peptide bonds.Proteins have three dimensional constructions. Primary construction is the amino acerb sequence.Secondary construction, alpha spiral, beta sheet. Secondary constructions are local, many parts of different secondary construction can be present in the same protein molecule.

    It on a regular basis repeats local constructions stabilized by H bonds. Third construction, is by and large stabilized by nonlocal interactions, most normally the formation of a hydrophobic nucleus, but besides through salt Bridgess, H bonds, disulfide bonds, and even post-translational modifications.Quaternary construction, formed by several protein Molecules normally called protein fractional monetary units. ( 1 )

    Figure 1: Structure of proteins

    There are several quantitative trials for finding whether aminic acids or proteins are present in solution.These trials are specific for the presence of peptide bonds, certain types of side ironss and the type of secondary construction present.Biuret trial determines if there is 2 or more peptide or not.The biuret reagent is made of Na hydrated oxide and Cu sulphate. The bluish reagent turns violet in the presence of proteins, and alterations to tap when combined with short-chain polypeptides. ( 2 )

    Figure 1: Biuret trial

    Ninhydrin detects if there is ammonium hydroxide or primary, secondary aminoalkanes or not.In ninhydrin trial, if reacts with these free aminoalkanes, a deep blue or violet colour will detect.

    Xanthoproteic trial, determines benzine and benzine derived functions such as tyrosine, tyrptophane which are contains activated benzene rings and readily undergo nitration and phenyl alanine which is besides contains benzene pealing but non activated and non readily undergo nitration.Also the merchandise will be xanthous colored. ( 3 )

    Heavy metal trial, makes ions to denaturate proteins.There are similar reagent with biuret trial and it uses AgNO3 and Fe ( III ) .

    3. Apparatus:

    3.1. Equipment:

    Test tubing ( 15 mL falcon ) * 16


    Test tubing rack

    Beaker 250 milliliter

    Hot topographic point

    Weighing dish


    3.2. Chemicals:

    2 % glycine solution

    2 % gelatin solution

    2 % albumin solution

    2 % tyrosine solution


    Banana Milk

    2.5 M NaOH solution

    Ninhydrin reagent

    Nitric acid

    5 % Cu sulphate

    5 % Ag nitrate

    5 % Fe ( III ) nitrate

    Sodium nitrate

    4. Procedure:

    5 tubings were labeled as 1,2,3,4,5 harmonizing to the strategy below:

    2 % glycine

    2 % gelatin

    2 % albumen


    2 % tyrosine

    For biuret trial ; 1 milliliter of each solution in 1,2,3 and 5 was placed except casein and casein was put and 1 milliliter H2O was added in trial tubing 4.

    7-10 beads of 2.5 M NaOH was added and 2 beads of 5 % Cu sulphate solution was added on each of the samples.

    Observations were recorded.

    For ninhydrin trial ; another 5 trial tubings were labeled.

    7-10 beads of ninhydrin reagent was added to each trial tubing and heated in a H2O bath for 5 proceedingss.

    Observations were recorded.

    For xanthoproteic trial ; another 5 trial tubings were labeled.

    10-15 beads of azotic acid was added to each trial tubing and heated in a H2O bath for 5-10 proceedingss.

    For heavy metal precipitation trial ; 2 milliliter milk was placed in 3 separate tubings and labeled as 1,2,3.

    10 beads of 5 % Ag nitrate was added to prove tubing 1, 10 beads of 5 % Fe ( III ) nitrate to prove tubing 2 and 10 beads of Na nitrate to prove tubing 3.

    Observatios were recorded.

    5. Observation:

    For biuret trial:


    Blue ( visible radiation )


    Purple ( dark )


    Purple ( igniter )


    Purple ( bluish & A ; purple )


    Blue ( igniter )

    For ninhydrin trial:


    immediately it becomes violet and now dark purple


    Before the bath it was fuzzed and now dark purple ( alterations color easy )


    Dark purple and like solid ( alterations color more easy )


    Grey & A ; purple ( non disassociate in H2O )


    Change colour to the purple easy than glycine

    For xanthoproeic trial:




    Fuzzy yellow


    First fuzzy xanthous so dark orange ( orange & A ; red )


    Fuzzy white so fuzzy yellow


    First light yellow, after orange, so dark orange & A ; Brown

    For heavy metal precipitation trial:

    Silver nitrate

    First, yellow. Then, light pink

    Iron ( III ) nitrate


    Sodium nitrate



    The purpose was, finding whether aminic acids or proteins are present in solution and amino acids are transporting a free aminoalkane group by utilizing biuret trial, ninhydrin trial, xanthoproteic trial and heavy metal precipitation trial.

    At foremost, the biuret trial was showed that if there was 2 or more peptide or not.Cupper ( II ) ion was complexed with amine group ( positive ) gave the violet colour. As a consequence of biuret trial, it was identified that Casein amino acids contain dual or more bond in their construction because they gave violet colour and it shows that the trial was positive.The ninhydrin trial was showed if there was aldehyde, ammonium hydroxide and free primary amine.The name of the composite was hydrindatin and the colour was violet. The aminic acids except casein has free aminoalkane group in their construction. The colourss were by and large dark purple

    The xanthoproteic trial showed if there was benzine or derived functions such as phenyl alanine, tyrosine, tryptophane, The colour was xanthous and tyrosine, tyrptophan, casein have yellow coloring material. So, it was understood that they have phenyl ring in their construction. The heavy metal trial showed that if ions denaturates proteins similar with biuret and used Fe ( III ) and AgNO3.

    First Na nitrate, Ag nitrate and Fe ( III ) nitrate have same colour yellow but the colour of Silver nitrate was changed to light pink and the otheraa‚¬a„?s colour were same ( xanthous ) .

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