Makindo Medical Notes

The Beta globin gene has 1,400 bases, while the dystrophin gene has 2,400,000 bases. These differences highlight the variation in gene length, complexity, and function within the human genome.

About Gene Structure

• Promoter Site:
  • The promoter is a specific region of DNA located at the beginning of a gene.
  • Its primary function is to bind RNA polymerase, the enzyme responsible for synthesizing RNA, and various transcription factors that help initiate transcription.
  • Without a functional promoter, a gene cannot be transcribed into RNA, preventing protein synthesis.
• RNA Polymerase II:
  • This enzyme synthesizes messenger RNA (mRNA) from the DNA template during transcription.
  • It is highly specialized for mRNA production, which carries genetic information from DNA to the ribosome for protein synthesis.
• Promoter Sequences:
  • The promoter contains specific DNA sequences that help position RNA polymerase and regulate the start of transcription.
  • Key sequences include:
    • TATA Box: Found around 25-35 bases upstream of the start site, the TATA box helps position RNA polymerase.
    • GC Box: Located upstream of the gene, the GC box binds transcription factors that enhance gene expression, particularly in genes transcribed at high levels.
• Start Site for Transcription:
  • This is the precise location where RNA polymerase begins to transcribe DNA into RNA.
  • It marks the start of the mRNA sequence and is located just downstream of the promoter region.
• Exons:
  • Exons are segments of DNA that code for proteins and are transcribed into mRNA.
  • During mRNA processing, exons are spliced together to form the mature mRNA, which is then translated into a protein.
  • Each exon encodes part of the protein, and the sequence and number of exons can vary widely between genes.
• Introns:
  • Introns are non-coding regions of DNA located between exons.
  • They are transcribed into RNA but removed during mRNA processing, so they are not translated into protein.
  • The function of introns is not fully understood, but they may play roles in gene regulation and alternative splicing, allowing a single gene to produce multiple protein variants.
  • Over 97% of human DNA consists of introns and other non-coding sequences.
• Stop Site for Transcription:
  • This region signals RNA polymerase to stop transcribing DNA into RNA, marking the end of the gene.
  • It ensures that only the necessary length of RNA is produced for the specific gene, preventing unnecessary or harmful genetic information from being transcribed.