Genetic Expression and Viral RNA Quiz

Gene Expression and Retroviruses

• Cells can express genes at varying rates and levels, with non-transcribed DNA depicted in gray.
• Retroviruses, like HIV, possess RNA as genetic material and use reverse transcriptase to convert RNA into DNA upon entering host cells.
• Modification of the central dogma: DNA ↔ RNA → Protein.

Introns and Exons in Eukaryotic Genes

• Eukaryotic genes contain alternating coding regions (exons) and non-coding regions (introns).
• The β-globin gene has three exons and two introns, with introns often longer than exons.
• mRNA is synthesized as a complementary strand to DNA, with introns removed via splicing before mRNA exits the nucleus.
• Single-copy genes typically exist once in the genome, while gene families, like the α- and β-globin, can express multiple variants.
• Genes must contain exons, start and stop signals, and regulatory control elements.

Protein Synthesis Steps

• Four key steps involved in protein synthesis are:
  • Transcription
  • RNA processing
  • Translation
  • Post-translation processing

Transcription Process

• Transcription is the conversion of DNA information into RNA, resulting in three major types: mRNA, rRNA, and tRNA.
• Protein-coding genes are those that encode mRNAs, which express genetic information into proteins.
• Small interfering RNAs (siRNAs) play a role in gene regulation and are derived from longer precursor RNA.

RNA Types and Processing

• Primary transcripts (pre-RNA) are longer than functional RNAs and correspond to the complete DNA segment.
• Primary transcripts associate with proteins as they are synthesized, making them short-lived and requiring processing into smaller RNAs.
• RNA processing involves cut-and-paste reactions, needing small RNAs (90 to 300 nucleotides) and associated proteins.

Central Dogma Overview

• Proposed by Francis Crick in 1958, the central dogma explains genetic information flow within cells, showcasing RNA’s dual role in protein synthesis.
• The "RNA world" hypothesis suggests that early life forms may have been based on self-replicating RNA sequences, predating DNA and proteins.

Insights into Gene Function

• Archibald Garrod discovered in 1908 that certain inherited diseases stem from the absence of specific enzymes, termed "inborn errors of metabolism."
• Garrod investigated alcaptonuria, a metabolic disorder where urine darkens due to an accumulation of homogentisic acid, revealing a link between genetic defects and enzyme deficiencies.