Regulating Transcription & Translation (HL) (HL IB Biology)

• Only some DNA sequences code for the production of polypeptides, these are called coding sequences
• Non-coding sequences produce functional RNA molecules like transfer RNA (tRNA) or are involved in the regulation of gene expression such as enhancers or promoters
  • The promoter is a non-coding sequence located near a gene whereas enhancers are non-coding regions of DNA that are usually found further away from a gene
  • The promoter and enhancer regions are not themselves transcribed
• Transcription factors are a type of protein molecule that bind to the promoter or enhancer sequences to help initiate transcription
  • This helps RNA polymerase to attach to the promoter and result in an increase in the rate of transcription
  • These transcription factors regulate transcription and ensure that only the required genes are expressed in the correct cells, at the correct time and to the appropriate level depending on the specific needs of the cell
  • This is the most common way for cells to control gene expression

A transcription factor binding to the promoter region of a gene which allows RNA polymerase to bind and for transcription to occur

• Once mRNA molecules are synthesised during transcription, it is modified and transported to the ribosomes in the cytoplasm for translation
• Once translation of an mRNA molecule is complete, it will remain in the cytoplasm until it is broken down by enzymes called nucleases
  • In human cells, it may take anywhere from a few minutes to a couple of days before mRNA is broken down
  • Degradation of mRNA is a way for the cell to regulate the process of translation
  • This ensures that proteins are only synthesised when necessary and removes mRNA molecules which have already been translated