Biology: Gene Transcription and Translation

Transcription and Promoter Function in Prokaryotic Cells

• Gene Sequencing and Promoter Importance

  • The initial step in gene expression is sequencing the DNA to identify the promoter region.
  • The promoter is vital as it is the site where transcription initiation begins.

• Sigma Factor Role

  • The sigma factor is a protein that recognizes and binds to the promoter, specifically to sequences at the -10 and -35 regions of the promoter.
  • Once bound, the sigma factor recruits RNA polymerase to the promoter, initiating transcription.

• Impact of Removing Promoter

  • If the promoter sequence (about 35 nucleotides long) is absent from the gene, transcription will not occur.
  • Consequently, no mRNA will be produced, and the gene will not be expressed.

Differences Between Prokaryotic and Eukaryotic Transcription

• Lack of Sigma Factor in Eukaryotes

  • Eukaryotic cells do not possess sigma factors or the -10 and -35 promoter regions linked to transcription.

• Transcription and Translation Processes

  • In prokaryotic cells, transcription occurs in the nucleoid region without a nuclear membrane, allowing for simultaneous transcription and translation.
  • This quick and efficient process contributes to rapid bacterial growth; bacteria can multiply in as little as 15 minutes under favorable conditions.

• Health Implications

  • Eating contaminated food can lead to illness approximately four hours later due to rapid bacterial proliferation, resulting from quick transcription and translation processes.

Mechanism of Transcription in Prokaryotes

• Transcription and Translation Coupling

  • As transcription occurs, ribosomes can simultaneously bind to the mRNA, facilitating immediate translation of proteins even before transcription finishes.
  • The mRNA remains attached to the DNA during this process, which is a notable feature of prokaryotic cells.

• Eukaryotic Transcription Characteristics

  • In contrast, eukaryotic transcription takes place in the nucleus, where RNA polymerase is located.
  • After synthesizing pre-mRNA, it must be exported to the cytoplasm for translation, leading to a distinct separation between these processes.

Additional Points on Eukaryotic Gene Expression

• Upstream Sequences and Regulatory Proteins

  • Eukaryotes exhibit various unique DNA sequences upstream of transcription start sites that interact with different regulatory proteins.
  • This complexity is essential for gene expression modulation based on factors like hormonal signals.

• Hormonal Influence on Gene Expression

  • For example, hormones can alter protein synthesis in the body by regulating the expression of specific genes.