Genes in eukaryotic DNA contain coding (exons) and noncoding (introns) regions.
Structure of a Eukaryotic Gene
| Component | Function | Location | Mnemonic |
|---|---|---|---|
| Exons | Contain genetic information that codes for proteins or functional RNA | Exit the nucleus and are expressed | Ex = Exit + Expressed |
| Introns | Noncoding sequences regulate gene expression and allow exon rearrangement | Remain in the nucleus | In = IN nucleus |
Key Concepts
- Exons are retained in the mature mRNA and translated into protein.
- Introns are removed from hnRNA (heterogeneous nuclear RNA) during RNA splicing.
- Alternative Splicing allows different combinations of exons to form distinct mRNAs → multiple proteins from a single gene.
- Example:
- Immunoglobulin (Ig): secreted vs. membrane-bound forms
- Tropomyosin: muscle-type specific isoforms
- Dopamine receptors: variations in neuronal signaling
- Tumor cells: evade immune recognition by altering splicing
- Example:
Summary Table
| Process | Location | Purpose | Clinical Relevance |
|---|---|---|---|
| Transcription | Nucleus | DNA → hnRNA | Template creation |
| Splicing | Nucleus | Removes introns; joins exons | Mutations can cause abnormal splicing (e.g., β-thalassemia) |
| Alternative Splicing | Nucleus | Creates multiple mRNAs | Key for tissue-specific protein expression |
| Translation | Cytoplasm | mRNA → Protein | Dependent on correct splicing |
High-Yield Key Points to Remember
- Introns = Intervening, stay in the nucleus
- Exons = Expressed, exit the nucleus
- Alternative splicing ↑ protein diversity without ↑ gene number
- Mutations at splice sites → disease (e.g., β-thalassemia, systemic lupus erythematosus)
Learning Objective
By the end of this topic, students should be able to:
Differentiate between introns and exons, describe the role of alternative splicing, and identify clinical examples where splicing abnormalities lead to disease.
