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

PHARMD GURU Page 1 1) INTRODUCTION TO RNA PROCESSING AND PROTEIN SYNTHESIS: The journey of genetic information from DNA to RNA to protein represents the central dogma of molecular biology. This process is essential for cellular function, growth, and adaptation. It involves several critical steps, including transcription, RNA processing, translation, and gene regulation, all of which ensure accurate and efficient protein production. A. OVERVIEW OF GENETIC INFORMATION FLOW:  The central dogma describes the flow of genetic information: DNA → Transcription → RNA → Translation → Protein  This process is vital for converting genetic instructions into functional proteins that drive biological activities. B. IMPORTANCE OF RNA PROCESSING:  In eukaryotic cells, RNA molecules undergo significant post-transcriptional modifications before translation.  RNA processing enhances mRNA stability, ensures correct translation, and regulates gene expression.  Errors in RNA processing can lead to genetic disorders and cancers. C. PROTEIN SYNTHESIS AND CELLULAR FUNCTION:  Protein synthesis translates genetic information into functional proteins that act as enzymes, structural components, and signaling molecules.  Proper regulation ensures cells produce the right proteins in response to internal and external cues. 2) RNA PROCESSING: A. rRNA PROCESSING: Ribosomal RNA (rRNA) is a key component of ribosomes, the cellular structures RNA PROCESSING, PROTEIN SYNTHESIS, AND GENE REGULATION
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 4 5. POST-TRANSCRIPTIONAL MODIFICATIONS:  Base modifications (e.g., methylation, pseudouridylation) enhance tRNA stability and decoding accuracy. c) BIOLOGICAL SIGNIFICANCE:  Proper tRNA processing is crucial for error-free translation.  Defects in tRNA processing are linked to mitochondrial disorders and neurodegenerative diseases. C. mRNA PROCESSING: Messenger RNA (mRNA) processing is a crucial step in gene expression, ensuring the production of a mature, stable transcript for translation. a) STRUCTURE OF MATURE mRNA: 1) 5’ Untranslated Region (5’ UTR): Regulates translation efficiency. 2) Coding Region: Contains the information for protein synthesis. 3) 3’ Untranslated Region (3’ UTR): Influences mRNA stability and translation. 4) 5’ Cap and 3’ Poly(A) Tail: Protect mRNA from degradation and facilitate translation. b) STEPS IN mRNA PROCESSING: 1) 5' CAPPING:  A 7-methylguanosine cap is added to the 5' end of the transcript.  Functions:  Protects mRNA from degradation.  Facilitates ribosome binding for translation.  Aids in mRNA nuclear export. 2) SPLICING:  Introns (non-coding sequences) are removed, and exons (coding regions) are joined by the spliceosome.  Alternative Splicing allows a single gene to produce multiple protein isoforms.