Question

In bacteria, the unit of DNA that contains multiple genes under the control of a single promoter is called _____ The mRNA produced from this unit is referred to as _____ \(\mathrm{mRNA}.\) a. an operator, a polycistronic b. a template, a protein-encoding c. an operon, a polycistronic d. an operon, a monocistronic e. a template, a monocistronic

Short answer

The correct answer is c. an operon, a polycistronic.

Step-by-step solution

Understand the structure of bacterial DNA

The unit of DNA in bacteria where multiple genes are controlled by a single promoter is called an operon. This system allows bacteria to simultaneously control the expression of multiple genes.

Understand the type of mRNA produced

When such a collection of genes (an operon) is transcribed, the resulting mRNA is single but contains the information of all the genes in the operon. This mRNA is known as polycistronic mRNA, because it contains the information for several different proteins (polypeptides), which are encoded by different cistrons.

Choose the correct answer

Looking at the options, the description of an operon controlling multiple genes and leading to polycistronic mRNA correlates with option c. Hence, the correct answer is c. an operon, a polycistronic.

Key concepts

Polycistronic mRNA

In the bacterial world, where efficiency is key to survival, the concept of polycistronic mRNA is crucial. This type of mRNA is a messenger RNA that encodes multiple proteins. When bacteria transcribe a stretch of their DNA that includes an entire set of functionally related genes, they produce a single mRNA molecule that contains the information for several polypeptides. These gene clusters are called operons, and their mRNA is termed as polycistronic due to their multiple protein-coding potential.

• Polycistronic mRNA allows bacteria to streamline their protein synthesis process.
• The genes transcribed together often participate in related pathways.
• This organizational method enhances efficiency and adaptation in changing environments by co-regulating protein production.

Understanding this concept helps explain how bacteria can be so adaptive and efficient, as it allows them to regulate groups of genes that work together. It's a beautiful symphony of genetic regulation!

Bacterial DNA Structure

Bacterial DNA structure is impressively organized and compact, tailoring to their unicellular lifestyle. Unlike eukaryotes, bacterial DNA is not enclosed within a nucleus, but instead, it floats freely within the cell in a region referred to as the nucleoid. Despite this seemingly simpler arrangement, bacterial DNA is quite efficient.

• DNA in bacteria consists of a single, circular chromosome.
• This chromosome is supercoiled, allowing it to fit in the compact space of the bacterial cell.
• In addition to the main chromosome, bacteria often possess small, circular DNA molecules known as plasmids, which can carry additional genes.

The operon model is a prime example of how bacterial DNA's linear organization allows for direct and efficient control of gene expression. By housing functionally-related genes together, bacteria can ensure quick and coordinated responses to environmental signals.

Gene Expression Control

Gene expression control in bacteria is a highly coordinated process aiming to conserve energy and resources. Bacteria have evolved strategies to ensure that proteins are synthesized only when required. The operon model plays a central role in this regulatory framework.

• A single promoter controls an entire cluster of genes, which allows simultaneous expression and regulation.
• Operators, which are DNA sequences within or next to the promoter, can bind repressors that block transcription.
• Such negative control prevents wasteful synthesis of unnecessary enzymes, while activation mechanisms allow expression when needed.

These mechanisms underlie the dynamic nature of bacterial survival, as bacteria can swiftly adapt to nutritional changes or stress conditions. Understanding gene expression control in bacteria provides insights into their resilience and serves as the foundation for genetic engineering and antibiotic development.