Question

Please explain the difference between positive control, positive regulation,negative control and negative regulation pertaining to DNA.

Answer 1

operon means cluster of coordinately regulated genes. First ,we talk about positive and negative control--the control is actually the response the operon will show when no regulatory protein is present. In the case when negative control is being shown by DNA, the genes in the operon will be expressed unless they are switched off by a repressor protein. Thus the operon will be turned on constitutively (the genes will be expressed) when the repressor in inactivated. In the case when positive control is being shown by DNA, the genes are expressed only when an active regulator protein, e.g. an activator, is present. Thus the operon will be turned off when the positive regulatory protein is absent or inactivated.

Now we talk about positive and negative regulation,

Positive Regulation- In this, binding of specific protein such as activator is required for transcription to begin. For this, sometimes RNA polymerase is tethered to the promoter.

Negative Regulation- In this, binding of a specific protein such as repressor inhibits transcription from occurring. For this, DNA bound repressors often prevent RNA polymerase from binding to the promoter, or can block the movement of RNA polymerase.