Question

The DNA sequence, to which repressors may bind, that lies between the promoter and the first structural gene is called the _____ .

Short answer

The DNA sequence is called the operator.

Step-by-step solution

Identify the Function of the Sequence

The sequence in question has a specific role in the regulation of gene expression. It is bound by repressor proteins, which can inhibit transcription from proceeding.

Recognize the Location of the Sequence

This sequence is located between the promoter region, which initiates transcription, and the first structural gene, the segment of DNA that encodes for a protein.

Recall the Terminology

With the function and the position of this sequence known, it is clear that the term that describes it corresponds to a common genetic element involved in controlling gene expression.

Key concepts

Promoter Region

The promoter region of DNA is the launching pad for gene expression. It's where the transcription journey begins for RNA polymerase, the enzyme that synthesizes RNA from a DNA template. Think of it as the 'start button' for turning genes on. When a cell needs a specific protein, it sends signals that trigger the promoter to activate and recruit RNA polymerase.
However, promoters aren't just on-off switches; they work with other elements to precisely regulate gene expression. This is where other molecules, like repressors and activators, come into play. They can bind to sequences near the promoter, modifying how easily RNA polymerase can do its job—sort of like having a dimmer switch for lights. The sequence that repressors bind to, which is found between the promoter and the first structural gene, is essential for this intricate control system that determines when and how strongly a gene will be expressed.

Structural Gene

The stars of the genetic show are the structural genes. These segments of DNA carry the blueprints for proteins, which perform countless functions in your body. From enzymes that digest your food to antibodies that fight off infections, structural genes encode the instruction manuals for assembling these proteins.
A structural gene is essentially like a recipe in a vast cookbook, with the promoter region acting as the index that tells the cell's machinery where to start 'reading.' When the repressor proteins are not bound to the intervening sequences, transcription moves smoothly from the promoter to the structural gene, resulting in the production of RNA and, subsequently, the desired protein. By understanding this intricate relationship between promoter regions, repressors, and structural genes, we gain insight into the delicate balance of processes that underlie our very biology.

Transcription Inhibition

Transcription inhibition is like putting a roadblock in the path of gene expression. It's a critical mechanism that cells use to prevent the production of certain proteins when they aren't needed, avoiding wasteful use of resources.
How does this happen? Repressor proteins, when they bind to specific DNA sequences, act as the 'stop signal' for the transcription machinery. This binding can change the shape of the DNA or the promoter region in such a way that RNA polymerase can't attach or move to transcribe the gene. It's a bit like putting a cover over a light switch to prevent it from being flipped on inadvertently. This tightly controlled process ensures that genes are expressed only at the right times, conserving energy and maintaining the balance of protein levels within the cell. Understanding transcription inhibition offers insight into how genes can be turned off, and plays a pivotal role in various biological processes and medical applications, such as the development of antibiotics and cancer treatment strategies.