Structural organization of the protein molecule
Proteins function in a native conformation, which includes tertiary or quaternary structure. The stability of this spatial arrangement is maintained primarily by weak interactions: hydrogen bonds, ionic (electrostatic) forces, hydrophobic contacts, and van der Waals forces, as well as stronger covalent disulfide bonds.
Molecular chaperones (or heat shock proteins) are responsible for proper folding and preventing the aggregation of partially folded chains.
Temperature effects and denaturation
Raising the temperature above $40^\circ\text{C}$ critically affects biopolymers:
- The kinetic energy of atoms inside the protein molecule increases sharply.
- The weak bonds holding the native spatial structure together are disrupted.
- The polypeptide chain unfolds, leading to denaturation.
- Changes in the shape of active sites lead to the loss of enzymatic, transport, and structural activity, disrupting cellular metabolism.
Protein classification
Protein molecules are classified according to several main criteria:
| Sign | Types and characteristics |
|---|---|
| By composition | Simple (amino acids only) and complex (conjugated proteins with a prosthetic group, e.g., hemoproteins) |
| By shape | Compact globular and elongated fibrous proteins |
| By function | Enzymatic, structural, contractile, transport, protective, and receptor |
| By membrane localization | Peripheral and integral proteins (including transmembrane) |
Protein families and mineral components
Groups of proteins with homologous sequences, similar conformation, and related functions are combined into families (e.g., the myoglobin or immunoglobulin family).
Mineral components of the diet play an important role in protein function. However, their excess leads to pathologies: excess iron and copper trigger Fenton reactions with the formation of toxic radicals, excess zinc causes antagonism with copper, excess selenium leads to selenosis, and high doses of chromium are nephro- and hepatotoxic.
Weak bonds maintain the protein shape (hydrogen, ionic, hydrophobic), and high temperature ($>40^\circ\text{C}$) disrupts them, causing denaturation.
Class and exam questions
What types of bonds maintain the native conformation of a protein?
The native tertiary or quaternary structure is maintained primarily by weak bonds: hydrogen, ionic, hydrophobic interactions, and van der Waals forces, as well as covalent disulfide bridges.
What happens to a protein at temperatures above 40°C?
A sharp increase in the kinetic energy of atoms occurs, along with the disruption of weak bonds, unfolding of the polypeptide chain (denaturation), and complete loss of biological function.
What is the difference between simple and complex proteins?
Simple proteins consist exclusively of amino acid residues, whereas complex proteins contain a tightly bound non-protein moiety—the prosthetic group.
What else to study on this topic
- Mechanisms of action of molecular chaperones during folding
- The role of covalent modifications of membrane proteins (acylation, glycosylation, phosphorylation)
- Biochemical functions of zinc, selenium, chromium, copper, and iron
- Free radical processes and the Fenton reaction
- Classification of complex proteins by the type of non-protein component (chromoproteins, nucleoproteins, lipoproteins, glycoproteins, and metalloproteins)
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