The Tertiary Structure is Stabilized by R-Group Interactions
Definition
Tertiary structure
The tertiary structure of a protein refers to the complete three-dimensional folding of a single polypeptide chain.
- The tertiary structure of a protein refers to the complete three-dimensional folding of a polypeptide chain.
- This structure is stabilized by specific interactions between the R-groups (side chains) of amino acids.
Hydrogen Bonds
- Form between slightly positive hydrogen atoms (e.g., in -OH groups) and electronegative atoms like oxygen in C=O groups.
- These bonds are weak individually but collectively provide significant stability.
Hydrogen bonds are highly sensitive to changes in temperature and pH. Extreme conditions can disrupt these bonds, leading to protein denaturation.
Ionic Bonds
Definition
Ionic bonds
- Definition:
Ionic bonds form between R-groups that carry opposite charges.
- Occur between positively charged R-groups (e.g., -NH3⁺) and negatively charged R-groups (e.g., -COO⁻).
- Stronger than hydrogen bonds but sensitive to pH changes, which can disrupt charges.
- Students often confuse ionic bonds in proteins with salt bridges in inorganic chemistry.
- Remember, in proteins, ionic bonds depend on R-group charges, which can change with pH.
Disulfide Bonds
Definition
Disulfide
Disulfide bonds are covalent bonds that form between two cysteine amino acids.
- Covalent bonds formed between two cysteine residues.
- These are the strongest stabilizing interactions, providing rigidity, especially in extracellular proteins.
Hydrophobic Interactions
- Non-polar R-groups cluster in the interior of the protein to avoid water, while hydrophilic R-groups are exposed to the aqueous environment.
- This folding minimizes energy costs and stabilizes the structure.
- Think of hydrophobic interactions like oil droplets clustering together in water.
- Just as oil avoids mixing with water, hydrophobic R-groups avoid the aqueous environment.
Interplay Between Interactions
- Combined Effect: The tertiary structure of a protein results from the combined effect of hydrogen bonds, ionic bonds, disulfide covalent bonds, and hydrophobic interactions.
- Stabilization:
- Hydrogen Bonds and Ionic Bonds: Stabilize specific regions and interactions within the protein.
- Disulfide Bonds: Provide rigid stability, especially in extracellular proteins.
- Hydrophobic Interactions: Drive the overall folding pattern, creating a compact and stable structure.
Chaperone proteins assist in folding by ensuring that these interactions occur in the correct sequence and locations, preventing misfolding.
Self review- What happens to the tertiary structure of a protein when it is exposed to high heat or acidic conditions?
- How do these changes affect its function?
