MES 3

Detailed Notes on Cellular Biomolecules Related to Upper Respiratory Tract Infections (URTI)

Overview

This document elaborates on the key concepts of Cellular Biomolecules, particularly focusing on DNA transcription and translation in the context of Upper Respiratory Tract Infections (URTI). These notes are prepared for students of the National University of Malaysia as part of the MD Programme Package Series in the Faculty of Medicine.

Objectives

By the end of this educational segment, students are expected to:

1. Describe DNA Transcription and Translation:

   • DNA Transcription: The process where a specific segment of DNA is copied into RNA by the enzyme RNA polymerase. This occurs in the nucleus in eukaryotes and in the cytoplasm in prokaryotes.

   • DNA Translation: The subsequent process where the mRNA sequence is used to synthesize proteins through the ribosomal machinery, involving tRNA and various initiation, elongation, and termination factors.

2. Explain the Differences Between Prokaryote and Eukaryote Translation:

   • Prokaryotic Translation: Transcription and translation occur simultaneously in the cytoplasm. Ribosomes attach to the mRNA as soon as it is synthesized. Prokaryotic mRNA is polycistronic, meaning one mRNA can encode multiple proteins.

   • Eukaryotic Translation: Occurs in the cytoplasm after transcription in the nucleus and involves extensive post-transcriptional modifications of mRNA, such as capping, polyadenylation, and splicing. Eukaryotic mRNA is monocistronic, coding for only one protein.

3. Explain the Mechanism of Action of Inhibitors for DNA Transcription and Translation:

   • Erythromycin inhibits protein synthesis in prokaryotes by binding to the 50S ribosomal subunit, hindering the translocation step of translation.

   • Other Inhibitors:

     • Streptomycin: Binds to the 30S ribosomal subunit, interfering with the initiation of protein synthesis.

     • Tetracycline: Prevents the binding of aminoacyl-tRNA to the A site of the ribosome, thus blocking protein synthesis.

     • Chloramphenicol: Inhibits the peptidyl transferase activity of the 50S ribosomal subunit, preventing peptide bond formation.

     • Rifampicin: Targets RNA polymerase, thus inhibiting mRNA synthesis during transcription.

4. Describe the Mechanism of Action of Erythromycin:

   • Erythromycin exerts its effect by binding to the 50S ribosomal subunit, thus blocking the peptide exit tunnel, effectively halting protein synthesis and promoting bacterial cell death or growth inhibition.

5. Explain How Bacteria Develop Resistance to Antibiotics:

   • Bacteria can become resistant through:

     • Genetic Mutations: Changes in their genetic material can lead to alterations in their ribosomal structure or enzyme functionality, making them less susceptible to antibiotics.

     • Horizontal Gene Transfer: Through transformation, transduction, or conjugation, bacteria can acquire resistance genes from other bacteria.

     • Enzymatic Inactivation: Some bacteria can produce enzymes that chemically modify antibiotics (e.g., β-lactamases) rendering them ineffective.

References:

• Lippincott’s Illustrated Reviews: Biochemistry

• Marks’ Medical Biochemistry

• Harper’s Biochemistry

This educational material is proprietary to Universiti Kebangsaan Malaysia and cannot be reproduced without written consent.