Question

What is an enhancer region?

Answer 1

for any gene to express itself it must have a promoter to which transcription factors bind. Binding of transcription factors to the promoter region facilitates the subsequent binding of RNA polymerase to the gene , thus leading to transcription followed by translation of the gene. But this binding of transcription factors to the promoter leads to what is called " basal expression " of the gene ie under normal conditions 10 mRNAs and thus 10 proteins are produced from this single gene . Now suppose the cell is in a scenario where it receives a signal that tells it to synthesize 100 protein molecules from the same gene. However basal expression will lead to the synthesis of only 10 protein molecules whereas the cells requirement is 100.. This is where the role of enhancers come into picture. Just like promoters enhancers are also DNA sequences to which proteins , called ACTIVATOR proteins, bind leading to an increased gene expression (beyond basal expression) .

have a look at the uploaded image. In the image the sky blue molecule with a tail , resembling a rat , is the RNA polymerase.

However there is a key difference between promoters and enhancers. Promoters are located ADJACENT to the genes . Unlike promoters , enhancers are generally FAR away UPSTREAM of the gene . The looping of the DNA between the promoter and the enhancer brings the proteins bound to these regions into close proximity thus facilitating increased gene expression . Enhancers can also be located WITHIN the gene and also DOWNSTREAM of the gene .
In short promoters are located adjacent to genes , enhancers can be located upstream/downstream/within the gene.