Gene Expression P2

DNA Methylation

• Definition: Addition of a methyl group (CH3) to DNA, affecting gene expression.

• Function:

  • Methyl groups added to cytosine nucleotide result in gene silencing, inhibiting transcription.

  • Conversely, removing methyl groups "activates" the genes, allowing transcription to occur.

• Significance:

  • Regulates gene expression, preventing unnecessary protein synthesis and conserving energy.

  • Example: E. coli activates or deactivates genes related to trypsin based on intestinal needs.

Chromatin Modification

• Definition: Structural changes to chromatin (DNA + proteins) that impact gene accessibility.

• Role of Acetyl Groups:

  • Presence of acetyl groups added to histones exposes DNA, permitting transcription.

  • Absence of acetyl groups tightens histone-DNA interaction, restricting gene expression.

• Mechanism: Acetylation vs. Methylation

  • Acetylation: Increases accessibility, allows transcription.

  • Methylation: Decreases accessibility, prevents transcription.

RNA Interference (RNAi)

• Definition: Regulatory mechanism controlling gene expression post-transcriptionally.

• Key Components:

  • MicroRNAs (miRNAs) and small interfering RNAs (siRNAs) are involved with enzymes forming silencing complexes.

• Mechanism:

  • RISC (RNA-induced silencing complex) degrades target mRNA or inhibits translation, silencing the gene.

  • Prevents the production of proteins from specific genes when not needed.

Importance in Gene Regulation

• Both DNA methylation and chromatin modification are vital for adaptive responses to cellular needs.

• They ensure that proteins are synthesized only when required, maintaining metabolic efficiency.

• Understanding these processes is fundamental for advancements in genetic research, biotechnology, and medicine.