Biomolecules - Structure of proteins (Primary, secondary, tertiary, quaternary)
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Proteins are polymers of -amino acids linked by peptide bonds (amide linkages). The structure is organized into four levels of complexity.
Primary Structure: Refers to the specific sequence of amino acids in a polypeptide chain. Any change in this sequence creates a different protein. The amino acids are held by covalent peptide bonds .
Secondary Structure: Refers to the shape in which a long polypeptide chain can exist. It results from hydrogen bonding between the and groups of the peptide bond. Common types are the -helix (intramolecular H-bonding) and -pleated sheet (intermolecular H-bonding).
Tertiary Structure: Represents the overall folding of the polypeptide chains, giving a three-dimensional shape (Fibrous or Globular). It is stabilized by -bonds, disulfide linkages (), van der Waals forces, and electrostatic forces of attraction.
Quaternary Structure: Some proteins consist of two or more polypeptide chains referred to as sub-units. The spatial arrangement of these sub-units with respect to each other is known as the quaternary structure.
Denaturation: A process where a protein loses its biological activity due to changes in temperature or , which disrupts the secondary and tertiary structures while leaving the primary structure intact.
📐Formulae
💡Examples
Problem 1:
What happens to the structure of a protein during the boiling of an egg?
Solution:
When an egg is boiled, denaturation of protein (albumin) occurs. The heat causes the -bonds to disturb, leading to the unfolding of the globular protein. The secondary and tertiary structures are destroyed, but the primary structure (sequence of amino acids) remains intact. This results in the coagulation of the egg white.
Explanation:
Denaturation involves the loss of conformation due to the breaking of weak bonds like hydrogen bonds, while covalent peptide bonds are strong enough to withstand the heat.
Problem 2:
Compare the hydrogen bonding in -helix and -pleated sheet structures.
Solution:
In an -helix, a polypeptide chain forms all possible hydrogen bonds by twisting into a right-handed screw with the group of each amino acid residue hydrogen-bonded to the of an adjacent turn. In a -pleated sheet, all peptide chains are stretched out to maximum extension and then laid side by side, held together by intermolecular hydrogen bonds.
Explanation:
-helix utilizes intramolecular hydrogen bonding (within the same chain), whereas -pleated sheet utilizes intermolecular hydrogen bonding (between different chains or segments).