Tertiary structure refers to the spatial arrangement of secondary structures in a protein. It is stabilized through hydrogen bonds, ionic interactions, hydrophobic interactions, and disulfide bonds. There are two main classifications of protein tertiary structure - globular proteins which have a spheroid shape with abundant secondary structures, and fibrous proteins which are rod-shaped with one predominant secondary structure like collagen. Quaternary structure refers to the structure formed when two or more protein subunits (polypeptide chains) combine through non-covalent interactions. Denaturation involves the unfolding of protein structures due to factors like heat, salts, pH, or mechanical action and is partially reversible. Coagulation follows denaturation and involves the irre

1. Tertiary Structure
• Tertiary structure of proteins= spatial
arrangement of the secondary structures
(folding of domains)
• Stabilization: between side chains of AAs
• 1) hydrogen bonds
• 2) ionic (electrostatic) interactions
• 3) hydrophobic interactions
• 4) disulfide bonds

3. Classification of proteins according to
tertiary structure
• 1) globular proteins(sphero proteins)
• spheroidal shape
• both secondary structures are abundant
• 2) fibrous proteins(sclero proteins)
• rod-like shape
• one secondary structure predominates
• e.g. α-keratin, collagen

4. Quaternary Structure
• oligomeric structure of a protein (2 or more
• subunits ~ monomers)
• i.e. the structure is found only in proteins
• composed from 2 or more chains (subunits)
• Stabilization: non covalent interactions

5. Denaturation
Denaturation is the change in structure of protein molecules. The
process results in the unfolding of molecules. Factors which
contribute to denaturation are heat, salts, pH and mechanical
action.
Denaturation is a partially reversible change. For example, when an
egg white is whisked it incorporates air to form a foam.
If the foam is left to stand, it will
collapse back to form liquid
egg white.

6. Coagulation
Coagulation follows denaturation. For
example, when egg white is cooked it changes
colour and becomes firmer or sets.
The heat causes egg proteins to unfold from
their coiled state and form a solid stable
network.
This change is irreversible.

7. Coagulation
Another form of coagulation occurs in the production of cheese.
Rennin (an enzyme from a calf’s stomach) is added to milk
causing the protein casein to clot, producing curds (solid) and
whey (liquid).
Other applications of coagulation are:
• yogurt production;
• thickening of sauces with beaten egg;
• binding ingredients together, e.g. fish, cakes,
reformed meats;
• providing a coating for products, e.g. scotch eggs.

8. Gluten development
A cross section is shown below of under developed
dough and weak or soft flour 8% respectively.
Products that require short or non-elastic textures,
such as biscuits and cakes, use flours with lower
protein contents.

9. Gelation
Gelatine is a protein which is extracted from collagen, present in
connective tissue in meat.
When it is mixed with warm water the gelatine protein molecules
start to unwind.
Although on cooling a stable network is formed, trapping the liquid.
Gelation is reversible.