A dimer is a molecular complex formed when two similar or identical molecules (called monomers) bind together, usually through non-covalent interactions or covalent bonds. Dimers are commonly seen in proteins, nucleic acids, and receptors, and they often play critical roles in cell signaling, structural integrity, and gene regulation.
🔑 Definition:
A dimer is a compound or molecular complex consisting of two monomers (identical or different) that are chemically or physically bonded.
🧬 Types of Dimers:
| Type | Description | Example |
|---|---|---|
| Homodimer | Two identical monomers form the dimer | p53 tumor suppressor protein |
| Heterodimer | Two different monomers form the dimer | NF-κB (p65 and p50 subunits) |
🔬 How Dimers Form:
- Non-covalent interactions: hydrogen bonds, ionic interactions, hydrophobic forces (common in reversible protein dimers)
- Covalent bonds: disulfide bridges (common in stable structural dimers)
Some dimers form spontaneously, while others require:
- Ligand binding
- Post-translational modifications
- Environmental conditions (e.g., pH, temperature)
⚙️ Functions of Dimers in Biology:
| Function | Role |
|---|---|
| Signal transduction | Many receptors dimerize upon ligand binding (e.g., growth factor receptors) |
| Gene regulation | Transcription factors often bind DNA as dimers (e.g., NF-κB) |
| Enzyme activity | Some enzymes function only when in dimeric form |
| Structural stability | Dimerization increases protein stability and specificity |
🧠 Examples:
- NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells)
Forms a heterodimer (typically p65/p50) to regulate immune-related genes. - Insulin receptor
Functions as a dimer — insulin binding brings the receptor halves together to initiate signaling. - DNA-binding proteins like homeodomain proteins often bind DNA as dimers to increase affinity and specificity.
📌 Summary:
A dimer is a structure made up of two monomer units, joined either covalently or through weaker interactions. Whether identical (homodimer) or different (heterodimer), dimers are essential for many biological processes — especially in signaling, regulation, and structural support.