Role Of Sigma Factors And Repressors

Back to: MICROBIOLOGY 200 LEVEL

Welcome to class!

Hello, superstar! You’ve been walking through these microbiology topics with so much drive and curiosity — it’s inspiring! Today, we’re looking at two important players in gene regulation: sigma factors and repressors. These might sound like big scientific terms, but by the end of this lesson, you’ll see they’re simply like traffic wardens and gatekeepers helping cells know when to work and when to rest.

Role Of Sigma Factors And Repressors

Think about the last time you were at a big roundabout in Lagos or Abuja during rush hour. Without a traffic warden, everything would be a mess — cars wouldn’t know when to go or stop. Similarly, in bacteria, there are special proteins that help the cell know when to start or stop expressing certain genes. These are called sigma factors and repressors.

They help the cell stay organised, respond to changes in the environment, and save energy — just like a well-run Nigerian household during a fuel scarcity. Now let’s break them down in a simple, relatable way.

Sigma Factors – The Traffic Wardens of Transcription

Sigma factors are proteins that help RNA polymerase find the right starting point on the DNA during transcription.

Without them, the polymerase would wander aimlessly on the DNA strand.

Sigma factors bind to promoters (specific start sites on DNA), guiding RNA polymerase to start transcribing the right gene.

Bacteria have different sigma factors for different conditions:

σ⁷⁰ (sigma 70) is the most common — like your everyday uniformed warden.

Others come in during stress, heat, or starvation — like emergency responders in disaster times.

Think of sigma factors like an MC at a wedding who calls on the right speaker at the right time. No confusion, no noise — everything is well-organised!

Repressors – The Gene Gatekeepers

Repressors are proteins that block gene expression by binding to the operator region of the DNA.

When a repressor is in place, RNA polymerase cannot proceed — transcription is paused.

Example: In the lac operon, a repressor blocks the genes for lactose digestion when lactose isn’t available.

Repressors are like a gate man who locks the gate when there’s no visitor. He only opens it when there’s someone important — in this case, a molecule like lactose that removes the repressor.

Let’s say your school principal (sigma factor) assigns a prefect to guide students to their classes. Without that guide, students wander around. That’s like RNA polymerase without a sigma factor.

Now imagine the gate to the chemistry lab is locked (repressor) and only opened when your teacher brings the correct key (inducer). That’s how repressors control which genes get expressed.

Summary

• Sigma factors help RNA polymerase start transcription by guiding it to the promoter.
• Different sigma factors are used depending on the cell’s condition.
• Repressors block transcription by binding to the operator region on DNA.
• Sigma factors act like coordinators, while repressors are blockers that prevent unnecessary gene expression.
• Together, they help the cell control gene expression efficiently and wisely.

Evaluation

1. What role does a sigma factor play in transcription?
2. Give one example of a condition that may require a special sigma factor.
3. How does a repressor protein stop gene expression?
4. What is the operator region in DNA?
5. Use a real-life Nigerian scenario to describe the function of repressors.

You’ve just unlocked a new level of understanding in microbiology! Remember, it’s not just about reading — it’s about making sense of life itself. With Afrilearn, every topic becomes simpler, relatable and made just for you. Keep shining, and I’ll see you in the next class — you were born to excel!