KEGS Biology Blog

Thursday 4th October Section 3
October 5, 2012, 9:17 am
Filed under: Uncategorized

Primary and secondary proteins. Biuret test


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Biuret Test:

-Potassium Hydroxide added to test sample
-Few drops of dilute copper sulphate solution added
-Protein will change colour light blue to purple.
-Purple = Positive
-Blue = Negative

Proteins are polymers made of amino acid monomers where the long chains may be folded and twisted.

Primary Structure:

– The primary structure of protein is given by the specific sequence of amino acids that make up the protein.

Secondary Structure:

Hydrogen bonds form between adjacent
-NH and C=O groups
-Two possible formations are possible ( Both of which can occur within the same protein)
-Alpha Helix
-Beta Sheet(or Beta pleated Sheets)

The Structure Proteins:

Tertiary Structure
*Bonds are formed between R groups; 4 possible types depending on the chemical nature of the R groups
*R groups may be;

Disulphide Bridges are strong are strong covalent bonds between sulphur atoms of the amino acid cysteins.

Ionic Bonds are between the negatively charged, acidic R groups and positively charged, basic R groups. (Similar to the forces between Cl- and NA+ ions in NACL.

– Hydrophobic bonds or interactions are between R groups of non-polar amino acids. Eg: Valine and Leucine

-Hydrogen Bonds are formed between polar R groups and can only be broken by a high temperature or PH changes.

Example Question:

Describe a test which will indicate the presence of proteins:

-Answer: The Biuret test indicated the presence of proteins as when protein are present the colour changes from a light blue to purple when you add the agent.

Comment by meganbpotter

Structure of a Protein

“Proteins are made up of amino acids in a linear sequence, the amino group of one amino acid reacts with the carboxyl group of another amino acid in a condensation reaction releasing water. This reaction is called a peptide bond and the result of this reaction would be a dipeptide. If there are more than two amino acids bonded in this way it’s called a polypeptide.”

Comment by roobennithi

Comment by roobennithi

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