International baccalaureate biology sl investigation_detection of proteins by felix dyrek


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International baccalaureate biology sl investigation_detection of proteins by felix dyrek

  1. 1. Felix DyrekBiological Investigation: Detection of ProteinsIntroduction:The experiment was performed in order to observe the methods which can be used todemonstrate that proteins are present in different types of food.Research Question:In what kind of foods are proteins present and what kind of techniques are used to prove thepresence of proteins ?Hypothesis:If four samples of food,* two of which are known to be rich in protein* and two that lack in proteincome into contact with three different substances, being:* concentrated nitric acid (xanthoproteic reaction),* potassium hydroxide and copper (II) sulfate, together with potassium sodium tartrate, alsoknown as Biuret reagent , and* ethanol, 89% alcohol by volume (process of denaturation),then, the samples of ham and cheese will react to these substances, while lettuce and applesamples will not.Hypothesis Explanation:Ham and cheese are rich in protein,lettuce and apple are not.A xanthoproteic reaction will beproduced when the samples which are rich in protein being combined with nitric acid.Its alsocalled the xanthoproteic test in which a yellow acid substance is formed by the action of hotnitric acid on albuminous or proteid matter. It is changed to a deep orange-yellow color by theaddition of ammonia.In combination with biuret reagent,the blue reagent will turn into violet in case proteins arepresent.
  2. 2. Denaturation will appear when ethanol is added.Denatured proteins exhibit loss of solubility tocommunal aggregation.No change will occur if this substances are being combined with the lowprotein food apple or lettuce.Compounds:* apple* swiss cheese* iceberg lettuce* plain ham* concentrated nitric acid* Biuret reagent* ethanol (89%)Variables:* three reactant substances* the reaction of the combined protein foods and the substancesApparatus:* lab apron* gloves* knife* cutting board*12 test tubes* test tube rackMethod:1.Put on the apron2.Cut the cheese,apple,lettuce and ham small enough that it fits into the test tube
  3. 3. 3.Put the test tubes on a test table4.Put the gloves on,take a test tube and fill a small amount of nitric acid into the tube5.Observe what happens and write down your observations6.Do the same with the other test tubes7.Do the same again but this time use the biuret reagent and then the ethanol instead of nitricacid8.Write down your final observations Data Collection & Processing: Substance Sample of Food Observations Concentrated Nitric Acid ham Sample turned yellow, transparency increased (xanthoproteic reaction) cheese Turned almost orange, acid turned a bit cloudy lettuce No visible reaction apple No reaction, except apple turned a bit brown due to oxidizing with air Biuret reagent ham No visible reaction cheese No visible reaction lettuce No significant reaction – lettuce had a tinge of blue apple No visible reaction Ethanol ham No visible reaction cheese No visible reaction lettuce No visible reaction apple No visible reactionTable 1: Reactions observed in the experiment.Analysis & Conclusion:In conclusion the results of this experiment dont fit 100% with the suggestions but at least thexanthoproteic reaction prooved the presence of proteins and was therefore succesfull.runninganother experiment with more efficient samples might hopefully let me observe the actuallyexpactable outcomes.
  4. 4. Bibliography“Biuret reagent.” Wikipedia. February 18, 2008. March 2, 2008. <>“Denaturation (biochemistry)” Wikipedia. February 9, 2008. March 2, 2008.<>“Denature” The Free Dictionary by Farlex. 2003. March 2, 2008. <>Dolson, Laura. “List of High-Protein Foods and Amount of Protein in Each.” Low-Carb Diets. January21, 2008. March 2, 2008. <>“Low Protein Diets.” Every Diet. March 2, 2008. <>