3.1.4.1 Proteins - structure, function and biuret test Flashcards
What decides the amino acid sequence that determines the primary structure of a protein?
A DNA sequence
Describe the ionic bonds that hold the tertiary structure of a protein in place.
Weaker than disulfide bonds
Easily broken by changes in pH
Form between free carboxyl and amino groups in the polypeptide chain
What does Biuret reagent contain?
Concentrated Copper (II) sulfate solution
Describe the disulfide bonds that hold the tertiary structure of a protein in place.
Strong
Not easily broken
Occur between two cysteine amino acids
Name the bonds that hold the tertiary structure of a protein in place.
Disulfide Bonds
Hydrogen Bonds
Ionic Bonds
What do the below instructions describe:
- Place a 2cm3 of food in a test tube.
- Add 2 cm3 of sodium hydroxide solution at room temperature.
- Add a few drops of very dilute copper (II) sulfate solution (Biuret reagent)
- Observe and record colour change.
The Biuret test for proteins.
Identify the molecule

Amino acid

Name 3 fibrous type proteins
Collagen
Keratin
Silk
What is the monomer unit of a protein?
Amino acid
What do we call 2 amino acids chemically joined together?
Dipeptide
What is meant by a fibrous protein?
A protein made from many parallel polypeptide chains. These chains main form an α helix shape.
Fibrous proteins are usually insoluble in water.
Which colour does Biuret solution turn in the presence of protein?
Biuret changes from blue to purple.
Give 3 examples of enzymes
Amylase
Protease
Lipase
Which colour does Biuret reagent turn in the absence of protein?
It remains a blue colour
Identify the circled group

R group

Idenitfy the circled group

Amine group

What is meant by the tertiary structure of a protein?
When the α helix or β pleated sheets of the secondary protein structure are folded even more to give a complex, specific 3D structure.
What colour is Biuret reagent?
Blue
What is meant by a globular protein?
A protein made from few polypeptides, which form a spherical shape.
They are usually water soluble.
Describe the hyodrogen bonds that hold the tertiary structure of a protein in place.
Individually weak and easily broken
Cumulatively provide some strength
What is the polymer unit of a protein?
Polypeptide
What is meant by the secondary structure of a protein?
When hydrogen bonds form between the C=O and -NH groups of the amino acids that form a polypeptide. This causes a polypeptide chain to fold into a 3D shape such as an α helix or β pleated sheet.
How can a polypeptide be broken down into amino acids?
Hydrolysis
What is meant by the primary structure of a protein?
The sequence of the amino acids in the polypeptide that forms the protein.



