eukaryotic gene expression- lqc 6c

Question 1

how can a gene be switched on and expressed

Answer 1

• the DNA of a gene is uncoiled exposing the DNA to be transcribed
• A regulator protein (transcription factor) and the enzyme RNA polymerase both attach to the promoter region on DNA
• The gene is switched on, so can be expressed The gene is transcribed to make mRNA
  The mRNA is translated to make the protein

Question 2

Explain how a gene can be switched off

Answer 2

• A protein repressor molecule attaches to the DNA of the promoter region
• The attachment site for RNA polymerase and regulator protein (in promoter region) is blocked, so they cannot bind to the DNA
• A protein repressor molecule could also attach to the regulator protein, preventing it binding to the DNA

Transcription cannot take place, so no mRNA is made

No mRNA to be translated means no protein is made

The gene is not expressed

Question 3

explain the process of differential gene expression

Answer 3

• The correct chemical stimulus is required (e.g. a hormone, but read the question)
• Some genes are ‘switched on ’ and other genes are ‘switched off ’
• mRNA is made during transcription ONLY from ‘switched on’ genes and this mRNA is
  translated to produce proteins , so different proteins are made in different cells
• proteins determine the structure and function of cells, as the different proteins produced permanently modify a cell in different ways, resulting in different types of specialised cells being produced