Post-Transcriptional and Post-Translational Regulation Notes

Post-Transcriptional and Post-Translational Regulation

  • Definition: Regulation occurring after transcription and translation affecting gene expression at the RNA or protein levels.

Spliceosomes

  • Are complex molecular machines composed of proteins and RNA that facilitate splicing of pre-mRNA.
  • In eukaryotes, they process pre-mRNA by removing introns and joining exons.

Transcriptional Regulation

  • Involves controlling transcription initiation and gene expression levels.
  • Interplays between DNA, mRNA, and proteins are crucial for gene expression management.

Untranslated Regions (UTRs)

  • 5' UTR and 3' UTR: Regions flanking the coding sequence of mRNA that can regulate translation and mRNA stability.
  • Can contain elements that affect both the initiation and termination of translation.

Riboswitches

  • A type of RNA element capable of changing conformation in response to small metabolite binding.
  • Function: Regulate gene expression by altering transcription or translation based on the binding conditions.
    • Example: Thiamin (Vitamin B1) binding to its riboswitch regulates the expression of genes involved in its biosynthesis.

Regulation of Iron in Mammalian Cells

  • Ferritin: An iron storage protein that increases translation when iron levels are high.
  • Transferrin Receptor: Transports iron into cells; its translation increases when iron levels are low.

RNA Processing

  • After transcription, pre-mRNA undergoes several RNA processing steps, such as:
    • Splicing: Removal of introns and ligation of exons.
    • Modifications:
    • 5' Capping: Addition of a 7-methylguanylate cap for ribosome recognition.
    • 3' Polyadenylation: Addition of a adenine tail increasing mRNA stability.
    • RNA Editing: Changes the nucleotide sequence of the RNA after transcription.

Alternative Splicing

  • Allows different combinations of exons in mature mRNA, allowing for the production of multiple protein variants from a single gene.
  • Up to 70% of human genes may undergo this process to diversify protein function.

Roles of Splicing Factors

  • Splicing Enhancers: Promote recognition of weak splice sites, allowing inclusion of certain exons.
  • Splicing Repressors: Prevent recognition of specific splice sites, affecting which exons are included in the mRNA.
  • Ensures that resultant proteins are accurately produced from the pre-mRNA.

Covalent Modification of Proteins

  • Post-translational modifications that alter a protein’s function.
  • Common types include:
    • Phosphorylation: Addition of phosphate groups, often regulating enzyme activity.
    • Acetylation: Affects protein function and interactions.
    • Methylation: Involves addition of methyl groups and can influence gene expressivity.
    • Ubiquitination: Marks proteins for degradation, thus controlling protein levels in the cell.
    • Enzymes such as kinases, methylases, and acetylases play crucial roles in these processes.