The tertiary structure of a protein molecule results from:

Options

A. hydrophobic bonding
B. electrostatic bonding
C. hydrogen bonding
D. all of these

Explanation

### Step-by-Step Solution:

1. **Understanding Protein Structure**:
- Proteins have different levels of structure: primary, secondary, tertiary, and quaternary. The tertiary structure refers to the overall three-dimensional shape of a protein, which is crucial for its function.

2. **Formation of Tertiary Structure**:
- The tertiary structure arises from the interactions and bonding between the R groups (side chains) of the amino acids that make up the protein.

3. **Types of Bonds in Tertiary Structure**:
- **Hydrogen Bonds**: These are weak bonds formed between the hydrogen atom of one amino acid and an electronegative atom (like oxygen or nitrogen) of another amino acid.
- **Hydrophobic Interactions**: Non-polar (hydrophobic) side chains tend to cluster together in the interior of the protein, away from water, leading to a stable structure.
- **Disulfide Bridges**: These are covalent bonds that form between the sulfur atoms of cysteine residues in the protein, providing additional stability.
- **Ionic Bonds**: Also known as electrostatic interactions, these occur between positively and negatively charged side chains of amino acids.

4. **Conclusion**:
- The tertiary structure of a protein results from all these types of bonding interactions: hydrogen bonds, hydrophobic interactions, disulfide bridges, and ionic bonds. Together, they contribute to the complex folding and stability of the protein.

### Final Answer:
The tertiary structure of a protein molecule results from all types of bonding interactions, including hydrogen bonds, hydrophobic interactions, disulfide bridges, and ionic bonds.

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