{"id":12773,"date":"2026-06-15T14:15:08","date_gmt":"2026-06-15T14:15:08","guid":{"rendered":"https:\/\/www.vedprep.com\/exams\/?p=12773"},"modified":"2026-06-15T14:21:00","modified_gmt":"2026-06-15T14:21:00","slug":"regulation-of-gene-expression","status":"publish","type":"post","link":"https:\/\/www.vedprep.com\/exams\/iit-jam\/regulation-of-gene-expression\/","title":{"rendered":"Regulation of gene expression (Operon concept): IIT JAM 2027"},"content":{"rendered":"

While eukaryotes have a ton of complex layers for this, prokaryotes keep it simple and organized using a system called an <\/span>operon<\/b>. <\/span>An operon is like a genetic power strip in regulation of gene expression<\/b>. Instead of plugging five different appliances into five different outlets, an operon clumps a group of functionally related genes under the control of a single switch\u2014the <\/span>promoter<\/b>. Here at VedPrep<\/strong><\/a>, we break down these molecular machines into pieces that actually make sense. Let’s look at the main parts of an operon:<\/span><\/p>\n\n\n\n\n\n\n\n\n
Component<\/strong><\/td>\nFunction<\/strong><\/td>\n<\/tr>\n<\/thead>\n
Promoter<\/b><\/span><\/td>\nThe landing strip where RNA polymerase sits down to start transcription.<\/span><\/td>\n<\/tr>\n
Operator<\/b><\/span><\/td>\nThe genetic traffic light located between the promoter and the genes; it decides if RNA polymerase can move forward.<\/span><\/td>\n<\/tr>\n
Repressor<\/b><\/span><\/td>\nA protein that acts like a roadblock. When it binds to the operator, transcription stops dead in its tracks.<\/span><\/td>\n<\/tr>\n
Inducer<\/b><\/span><\/td>\nA small molecule that acts like a key. It binds to the repressor, twists it out of shape, and pulls it off the operator.<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

Worked Example: Understanding the Lac Operon<\/b><\/h2>\n

The <\/span>lac<\/span><\/i> operon in <\/span>Escherichia coli<\/span><\/i> (<\/span>E. coli<\/span><\/i>) is the ultimate textbook example of how bacteria manage their food sources in regulation of gene expression<\/b>. <\/span>E. coli<\/span><\/i> prefers glucose because it is easy to burn for energy. But if glucose runs out and lactose is floating around, the bacterium flips on the <\/span>lac<\/span><\/i> operon to break down that lactose.<\/span><\/p>\n

This operon houses three structural genes: <\/span>lacZ<\/span><\/i>, <\/span>lacY<\/span><\/i>, and <\/span>lacA<\/span><\/i>. Normally, a protein called the <\/span>lac<\/span><\/i> repressor (made by the <\/span>lacI<\/span><\/i> gene) sits right on the operator, blocking RNA polymerase from moving forward. When lactose enters the cell, a tiny bit of it converts into allolactose. This is your inducer. It binds to the repressor, makes it let go of the DNA, and allows transcription to take off.<\/span><\/p>\n

Here is a classic question style you might see on your next exam practice paper:<\/span><\/p>\n

Question:<\/b> As per regulation of gene expression, <\/b>consider a mutant <\/span>E. coli<\/span><\/i> strain with a non-functional <\/span>lac<\/span><\/i> repressor protein. Will this strain be able to metabolize lactose in the absence of glucose?<\/span><\/p>\n