PROTEINS Flashcards
What are fibrous proteins?
Fibrous proteins have polypeptide chains running parallel, held by hydrogen and disulphide bonds, forming fiber-like structures. They are generally insoluble in water.
Give examples of fibrous proteins.
Keratin (in hair, wool, silk) and myosin (in muscles).
What are globular proteins?
Globular proteins have polypeptide chains that coil into a spherical shape and are usually soluble in water.
Give examples of globular proteins.
Insulin and albumins.
At how many levels can the structure and shape of proteins be studied?
Protein structure and shape can be studied at four levels: primary, secondary, tertiary, and quaternary.
What is the primary structure of proteins?
The primary structure refers to the specific sequence of amino acids in a polypeptide chain.
How does a change in the primary structure affect a protein?
Any change in the sequence of amino acids results in a different protein.
What is the secondary structure of proteins?
The secondary structure refers to the shape a long polypeptide chain can adopt, mainly α-helix and β-pleated sheet structures.
What causes the formation of secondary structures in proteins?
Secondary structures arise due to hydrogen bonding between the –C=O and –NH groups of the peptide bond.
What is an α-helix structure?
The α-helix is a right-handed screw-like structure where the –NH group of each amino acid residue forms a hydrogen bond with the C=O of an adjacent turn of the helix.
What is a β-pleated sheet structure?
In the β-pleated sheet, peptide chains are stretched to maximum extension and laid side by side, held together by intermolecular hydrogen bonds, resembling pleated folds of drapery.
What is the tertiary structure of proteins?
The tertiary structure refers to the overall folding of the polypeptide chain, forming fibrous or globular shapes.
What forces stabilize the secondary and tertiary structures of proteins?
Hydrogen bonds, disulphide linkages, van der Waals forces, and electrostatic forces of attraction.
What is the quaternary structure of proteins?
The quaternary structure refers to the spatial arrangement of two or more polypeptide chains (sub-units) in a protein.
What is a native protein?
A native protein is a protein found in a biological system with a unique three-dimensional structure and biological activity.
What is denaturation of a protein?
Denaturation occurs when a protein loses its biological activity due to physical (temperature) or chemical (pH) changes, causing unfolding of globules and uncoiling of helices.
Which protein structures are destroyed during denaturation?
Secondary and tertiary structures are destroyed, but the primary structure remains intact.
Give two common examples of protein denaturation.
- Coagulation of egg white on boiling.
- Curdling of milk due to lactic acid formation by bacteria.
