Title 25. RNA PROCESSING, PROTEIN SYNTHESIS, AND GENE REGULATION.pdf ✅

PHARMD GURU Page 2 responsible for protein synthesis. The proper processing of rRNA is essential for forming functional ribosomes. a) ROLE OF rRNA IN PROTEIN SYNTHESIS:  rRNA is the structural and functional core of ribosomes, facilitating mRNA translation.  Prokaryotic ribosomes (70S) consist of 50S and 30S subunits, while eukaryotic ribosomes (80S) contain 60S and 40S subunits.  rRNA catalyzes peptide bond formation and ensures proper alignment of mRNA and tRNA during translation. b) STEPS IN rRNA PROCESSING: 1. TRANSCRIPTION:  In eukaryotes, RNA polymerase I transcribes rRNA (except 5S rRNA, transcribed by RNA polymerase III) into a large pre-rRNA precursor.  In prokaryotes, rRNA is transcribed as a single precursor (30S rRNA), later cleaved into 16S, 23S, and 5S rRNA. 2. CLEAVAGE:  The pre-rRNA transcript undergoes precise endonucleolytic cleavages to generate functional rRNA components.  This produces 18S rRNA (small subunit) and 5.8S + 28S rRNA (large subunit) in eukaryotes. 3. CHEMICAL MODIFICATIONS:  rRNA undergoes extensive methylation and pseudouridylation, which stabilize rRNA structure and improve translation efficiency.  These modifications are directed by small nucleolar RNAs (snoRNAs). 4. ASSEMBLY INTO RIBOSOMAL SUBUNITS:  Processed rRNA combines with ribosomal proteins to form small and large ribosomal subunits.  The subunits are transported to the cytoplasm, where they assemble into functional ribosomes for protein synthesis.
PHARMD GURU Page 3 c) BIOLOGICAL SIGNIFICANCE:  Proper rRNA processing ensures accurate and efficient translation.  Mutations affecting rRNA processing can lead to ribosomopathies (e.g., Diamond- Blackfan anemia). B. tRNA PROCESSING: Transfer RNA (tRNA) is an adaptor molecule that translates mRNA codons into amino acids during protein synthesis. Proper processing of tRNA ensures accurate translation. a) STRUCTURE AND FUNCTION OF tRNA:  tRNA has a cloverleaf structure with the following key regions:  Acceptor stem (3’ end): Binds to a specific amino acid.  Anticodon loop: Binds to complementary mRNA codons during translation.  tRNA molecules undergo extensive modifications to enhance stability and functionality. b) STEPS IN tRNA MATURATION: 1. TRANSCRIPTION:  tRNA genes are transcribed by RNA polymerase III in eukaryotes, producing pre-tRNA. 2. CLEAVAGE AND TRIMMING:  The 5' end is processed by RNase P, while the 3' end is trimmed by RNase Z. 3. SPLICING:  Some tRNA precursors contain introns, which are removed by a tRNA-specific splicing mechanism. 4. ADDITION OF THE CCA TAIL:  The CCA sequence (3' end) is enzymatically added, allowing amino acids to attach.