Makindo Medical Notes

Related Subjects: |Protein metabolism |Protein Synthesis |Amino acids |Human Metabolism |Carbohydrates |Hydrogen and other Bonds

🧬 Messenger RNA (mRNA) carries genetic information from DNA → ribosomes, where it acts as a template for protein synthesis. It is produced through transcription, processed, and then exported to the cytoplasm for translation.

🪜 Steps of mRNA Production

• Transcription 📝 :
  • Initiation 🚦: Transcription factors + RNA polymerase II bind to promoter → DNA unwinds → RNA synthesis starts.
  • Elongation ➡️: RNA polymerase II moves along DNA, adding nucleotides 5' → 3'.
  • Termination 🛑: RNA polymerase encounters termination signal → transcript released.
• RNA Processing ⚙️ :
  • 5' Capping 🎩: 7-methylguanosine cap protects mRNA + aids ribosome binding.
  • Splicing ✂️: Introns removed, exons joined (spliceosome-mediated). ➡️ Allows alternative splicing → multiple proteins from one gene.
  • 3' Polyadenylation 🧵: Poly-A tail stabilises transcript + aids nuclear export.
• Export 🚪 :
  • Mature mRNA passes through nuclear pores → cytoplasm → ribosomes.

🎚️ Regulation of mRNA

• Transcriptional 📝: Controlled by enhancers, silencers, transcription factors.
• Processing ⚡: Alternative splicing + RNA-binding proteins regulate diversity.
• Stability ⏳: 5' UTR, 3' UTR and miRNAs influence degradation vs protection.

💊 Clinical Relevance of mRNA

• Genetic Disorders 🧩: Abnormal splicing → thalassaemias; dysregulated transcription → cancers.
• Therapeutics 💉:
  • mRNA vaccines (e.g. COVID-19) = synthetic mRNA encodes viral proteins → immune response.
  • Gene therapy: Functional mRNA delivery to bypass defective genes.

📌 Key exam tip: mRNA always has 5' cap + poly-A tail. If either is missing → unstable transcript or failed translation.

📖 Overview of Protein Synthesis

Protein synthesis = DNA → mRNA (transcription) → protein (translation). It requires mRNA, tRNA, ribosomes, and amino acids.

🔬 Stages of Protein Synthesis

• Transcription (nucleus) – as above: initiation, elongation, termination → pre-mRNA → processed mRNA.
• Translation (cytoplasm) :
  • Initiation 🚀: Ribosome binds 5' cap, finds AUG (start codon), initiator tRNA (Met) joins at P site.
  • Elongation ➡️: Aminoacyl-tRNAs deliver amino acids, peptide bonds form, ribosome translocates along mRNA.
  • Termination 🛑: Stop codon reached (UAA, UAG, UGA) → release factors free polypeptide.

🧩 Key Components

• mRNA 🧬: Genetic template.
• tRNA 🎯: Transfers amino acids; anticodon matches codon.
• Ribosome ⚙️: Protein factory (large + small subunits).
• Amino acids 🍽️: Building blocks joined by peptide bonds.

🎚️ Regulation

• Transcriptional: Control of which genes are switched on/off.
• Translational: Initiation factors, uORFs, microRNAs.
• Post-translational: Modifications (phosphorylation, glycosylation, ubiquitination) → alter function.

⚠️ Clinical Relevance

• Genetic disorders 🧩: e.g. cystic fibrosis, sickle cell anaemia.
• Antibiotics 💊: Tetracyclines, macrolides, aminoglycosides → inhibit bacterial ribosomes.
• Targeted therapies 🎯: Cancer drugs exploit abnormal protein synthesis regulation.

📝 Summary

Protein synthesis is essential for life. Errors → disease; regulation → therapeutic target. Key to understand: DNA transcription → RNA processing → mRNA export → translation into protein 🧬➡️💪.

📷 Diagrams

🧾 Example: DNA → Protein