[catherine wells]

catherine wells  asked the Naked Scientists:
   
Hi,
 
You often talk about genes being switched on and off. I have in my head a picture of a double helix with lots of old fashioned light switches sticking out of it - but seriously doubt this is correct.  What actually happens when genes are switched on and off.
  
Many thanks,

Cath

What do you think?

[khurrum]

hi cath..
u ask "What actually happens when genes are switched on and off."
actually genes are turned of and on during the embryonic level to start or cease the specific funtion of that gene.gene of and on is related to its expression.U start to think like that in every cell there is complte information of each and every thing in the form of genome but some cell converted to eye cell,other into liver cell and so on...this all is controlled by the gene on and of.When some genes turned on in specfic cell,that cell will be concverted into its specfic kind......
hplfuly u got my point
khurrum

[chris]

Hi Cath

Commonly, genes are controlled by chemicals called "transcription factors", which are proteins, usually phosphate-bearing proteins, which lock onto specific regions of the DNA and alter its shape or chemistry in such a way as to make an adjacent section of the DNA more or less accessible to the miniature machines (polymerase enzymes) that read the DNA code and turn it into gene products. Other modifications can also turn genes on and off including hormones - thyroxine from the thyroid gland binds directly to DNA to activate certain genes - whilst other enzymes can add or remove chemical groups (usually methyl or acetyl groups) from the proteins around which DNA is wound. This alters the shape of that section of the genetic code, making it more or less readable by the cell.

Using these mechanisms cells can achieve both short and long-term control of gene expression in a highly dynamic way.

Chris

[thedoc]

Listen to the answer to this question on our podcast.

[Jonathan Madriaga]

Gene expression is controlled by regulatory factors. For example, to turn on Ras gene, it requires GTPase, meaning that GDP is phosphorylated to GTP, thus activating Ras pathway. It can be turned off by sensor molecules and other regulator factors.

[kmiller755]

Gene expression is controlled by regulatory factors. For example, to turn on Ras gene, it requires GTPase, meaning that GDP is phosphorylated to GTP, thus activating Ras pathway. It can be turned off by sensor molecules and other regulator factors.

This is not right.  The Ras protein is activated/deactivated by exchange factors GAP and GEF.  However, the Ras gene itself is not directly turned on or off.  One should make a distinction between the _gene_ and the _gene product_ (or protein), as it pertains to the question of OP.