Genetics Essentials - Chapter 10: From DNA to Protein - Transcription and RNA Processing

Introduction

• Focus on transcription and RNA processing from the textbook "Genetics Essentials, Fourth Edition."
• Hypothesis: RNA was the original genetic material due to its ability to self-catalyze (ribozymes).
• DNA evolved later as a more stable carrier of genomic information.

RNA Structure

• RNA is directional with a 5' phosphate end and a 3' hydroxyl end.
• Differences from DNA:
  • Has a hydroxyl group on the 2' carbon (ribose sugar).
  • Contains uracil instead of thymine.
• Primary structure: Sequence of nucleotides (A, G, C, U).
• Secondary structures: Includes hairpin loops formed by base pairing within a single strand.

Types of RNA

• mRNA: Messenger RNA, found in bacteria, eukaryotes, and archaea, copies genes.
• rRNA: Ribosomal RNA, part of ribosome structure.
• tRNA: Transfer RNA, assists in translation.
• Other RNAs: Small nuclear RNAs, microRNAs, long non-coding RNAs, CRISPR RNAs, etc.
• Ribozymes: RNA molecules with enzymatic activity, sometimes forming complexes with proteins.

Central Dogma of Molecular Biology

• Information flow: DNA -> RNA -> Protein.
• Transcription (DNA to RNA) and translation (RNA to protein) are key processes.

Transcription Process

• Primary Structure of RNA: Complementary and antiparallel to template DNA strand.
• Transcription Bubble: Area where DNA unwinds for RNA synthesis.
• RNA Polymerase: Enzyme that catalyzes RNA synthesis.
• Promoter and Terminator: Regions on DNA where transcription begins and ends.

RNA Processing in Eukaryotes

• Splicing: Removal of intronic sequences to join exons.
• 5' Cap and Poly-A Tail: Modifications to stabilize mRNA and assist translation.
• Alternative Splicing: Allows one gene to produce multiple proteins.

Other RNA Types

• tRNA: Contains anticodon and amino acid attachment site. Forms cloverleaf structure.
• rRNA: Part of the ribosome, crucial for protein synthesis.
• miRNA and siRNA: Involved in gene silencing, usually preventing translation or degrading mRNA.
• CRISPR RNA: Used by prokaryotes as part of an immune defense mechanism.

Summary

• The chapter highlights the complexity and versatility of RNA in genetic processes.
• RNA's role in gene expression and regulation is critical in both prokaryotic and eukaryotic organisms.
• Understanding transcription, RNA types, and processing is foundational for advanced genetic studies.