Download so, where do you get all your protein? investigating

Name ________________________________________ per _____ date _______
SO, WHERE DO YOU GET ALL YOUR PROTEIN?
INVESTIGATING THE PROTEIN CONTENT OF VARIOUS FOODS
BACKGROUND INFORMATION
Proteins are the most complex and functionally diverse molecules of living organisms. Proteins compose enzymes,
hormones, hair, skin, blood cells and muscle tissue just to name a few and are therefore associated with meat products.
The basic elements of proteins are carbon (C) hydrogen (H), oxygen (O) and nitrogen(N).
The monomers (the individual building blocks…like glucose is for polysaccharides) of proteins are 20 different amino acids.
As a protein molecule is being constructed, one amino acid is chemically attached (bonded) to another. This attachment
is called a peptide bond. The amino acids are bonded together in unique combinations to create a polypeptide chain; lots
of peptide bonds. This chain is then folded into a unique, 3-D shape.
Testing for Proteins
The Biuret Reagent is made of sodium hydroxide and copper sulfate. The blue
reagent turns violet in the presence of proteins, and changes to pink when
combined with short chain polypeptides. In this lab you will test for the presence of
protein using the Biuret Test. Like the Benedict’s Reagent, Biuret Reagent contains
copper ions. These copper ions reflect off closely clustered amide groups of
proteins casting a violet color to a solution with proteins. This violet color is a
positive reaction in a Biuret Test.
Investigation question:
Objectives:
Prediction: If (some function of proteins you think is happening in the cells that
makes them have more proteins) increases then the amount of protein in the
food overall will be higher because…(EXPLAIN why this makes sense, explain the
science)
Independent & dependent variable
Diagram of experiment set-up with labeled treatments
Materials
Safety
Procedure help:
Testing for Protein with Biuret's reagent
 Add 2 mL of the liquid food sample to a clean, dry test tube
o If the food to be tested is solid, make an extract. Grind, crush or chop a small amount and put into a test tube
to a depth of about 2cm. Add a similar amount of distilled water and stir with a glass rod. Allow to stand for a
few minutes.
 Add 500 µL of Biuret's reagent
 Do the same with de-ionized water to prepare a negative control and with albumin (egg white) solution to prepare a
positive control
 Shake well and allow the mixture to stand for 5 minutes
 Observe and record any color change (digital pictures also recommended)
 Heating is usually not necessary.
 Biuret's reagent is very pale blue, much paler that Benedict's solution and a different shade of blue.
 Biuret's reagent will change from blue to violet, or purple, in the presence of protein.
 The intensity of the color depends upon the amount of Biuret's reagent used, and the amount of soluble protein
present.
Example data table:
Substance
Color Before
Water
Color After
Positive Test for
Protein