20.3 Regulation of transcription and translation

Question 1

What are the general principles involved in controlling the expression of a gene by controlling transcriptipon

Answer 1

1. For transcription to begin the gene is switched on by transcriptional factors that move from the cytoplasm into the nucleus
2. Each transcriptional factor has a site that binds to a specific base sequence of the DNA in the nucleus
3. When it binds, it causes this region of DNA to begin transcription
4. mRNA is produced and the information it carries is the translated into a polypeptide
5. When a gene is not being expressed, the site on the TF that binds to DNA is not active
6. As this site is inactive, transcription does not occur

Question 2

How can oestrogen begin transcription

Answer 2

1. Oestrogen is a lipid-soluble molecule and therefore easily dissolves through the phospholipid portion of membranes
2. Once inside the cytoplasm of a cell, oestrogen binds with a site on a receptor molecule of the TF. The shape of this site and the shape of the oestrogen molecule complement one another
3. By binding with the site, the oestrogen changes the shape of the DNA binding site on the TF, which can now bind to DNA (it is activated)
4. The TF can now enter the nucleus through a nuclear pore and bind to specific base sequences on DNA
5. The combination of the TF with DNA stimulates transcription of the gene that makes up the portion of DNA.