Regulation of Transcription on Gene Transcription - 20.3 Flashcards
What is oestrogen an example of?
Steroid hormone
What must happen for transcription to begin?
The gene must be switched on.
How is a gene switched on?
By specific molecules that move from the cytoplasm into the nucleus. These are called transcriptional factors.
How do transcriptional factors cause the process of transcription to begin?
Each transcriptional factor has a site that binds to a specific base sequence of the DNA in the nucleus. When it binds, it causes this region of DNA to begin the process of transcription.
What happens when a gene is not expressed?
The site on the transcriptional factor that binds to DNA Is not active. As the site on the transcriptional factor binding to DNA is inactive it cannot cause transcription and polypeptide synthesis.
What influence can hormones have?
Hormones like oestrogen can switch on a gene and thus start transcription by combining with a receptor site on the transcriptional factor. This activates the DNA binding site by causing it to change shape.
What type of molecule is oestrogen and what does this mean?
Oestrogen is a lipid-soluble molecule and therefore diffuses easily through the phospholipid portion of cell-surface membranes.
What happens to oestrogen once it is inside the cytoplasm of a cell?
Oestrogen binds with a site on a receptor molecule of the transcriptional factor. The shape of the this site and the shape of the oestrogen molecule complement one another.
What happens once oestrogen has blinded with the receptor site on the transcriptional factor?
The oestrogen changes the shape of the DNA binding site on the transcriptional factor, which can now bind to DNA.
What happens after the shape of the DNA binding site has changed and how does this lead to transcription taking place?
The transcriptional factor can now enter the nucleus though a nuclear pore and bind to specific base sequences on DNA. The combination of the transcriptional factor with DNA stimulates transcription of the gene that makes up the portion of DNA.
How does haemoglobin link to gene expression?
A haemoglobin molecule is made up of four polypeptide chains each known as a globulin. There are three types of globulin; alpha-globulin and beta-globulin (which are found in adult humans), and gamma-globulin (found in human foetuses. Humans have genes that code for the production of all three types of globulin. The production of the different haemoglobin depends upon which gene is expressed. This expression of these genes changes at different times during development.
