gene expression

• Explain how a single gene can give rise to proteins with different primary structures (2)

  -       Pre-MRNA splicing 

  -       Different exons are removed and re-joined in different sequences 

  -       Therefore, producing different sequences of amino acids
• Explain how genes can be expressed in some tissues and not in others (3)

  -       Chemical signals bind to receptors found only in some tissues 

  -       Regulating a transcription factor 

  -       Transcription factor interacts with the promoter region of the gene, allowing or preventing binding of RNA polymerase 

  -       Therefore, switching on or off transcription
• Explain how transcription factors could activate insulin gene expression in beta cells(3)

  -       Transcription factor interacts with promoter region on insulin gene 

  -       Allowing rna polymerase to bind 

  -       Therefore, allowing transcription of gene so MRNA for insulin is produced.
• Explain how groups of cells can produce the same enzyme (3)

  -       Genes can be activated or deactivated 

  -       These cells would receive the same chemical signals 

  -       All the cells would have the gene for the enzyme activated

  -       Resulting in the production of MRNA for the enzyme.
• Describe how stem cells can give rise to different types of cells(4)

  -       Different chemical signals activate different genes 

  -       Genes activated are transcribed and MRNA is produced 

  -       MRNA is translated into proteins which determine the structure or function of cells 

  -       diff genes activated results in different cells being produced due to different proteins