Catabolite Repression – Positive Control of Lac Operon
Catabolite repression is a positive control of the lac operon. If bacteria have glucose and lactose both in the environment, what will it do? A smart cell will first utilise glucose and only when it is depleted it will utilize lactose. But how is it controlling lac operon even in the presence of lactose? That is where catabolite repression or positive control of lac operon comes into play.
It involves CAP protein (Catabolite Activator Protein) which is an activator protein and is also known as CRP (cAMP Receptor Protein). CAP acts as a sensor for glucose. It activates transcription of the operon but only when glucose levels are low. CAP senses glucose indirectly through the ‘hunger signal’ molecule cAMP which is a central regulator to different nutrients in environment such as glucose.
00:10 introduction
02:37 structure of the operon
04:38 role of CAP 06:21 role of cAMP
08:09 mechanism of catabolite repression
11:10 comprehensive table of all scenario of presence or absence of glucose and lactose affecting the positive control of lac operon
15:35 graphical representation
17:04 explanation of why it is called catabolite repression
Have you watch the video on lac operon? If not watch it here to understand this topic better; Lac Operon – Negatively Controlled Inducible Operon.