Question

What does a bacterial RNA polymerase produce when it transcribes a protein- coding gene? a. rRNA b. tRNA c. mRNA d. snRNA

Short answer

The correct answer is c. mRNA, as it carries the genetic information from the DNA to the ribosome, where it is translated into a protein.

Step-by-step solution

Understanding rRNA

rRNA stands for ribosomal RNA. It is a component of the ribosome, which is the cellular structure where protein synthesis takes place. rRNA does not carry the genetic information needed to produce proteins, so it cannot be the product of a protein-coding gene transcription.

Understanding tRNA

tRNA stands for transfer RNA. It is a small RNA molecule that carries amino acids to the ribosome during protein synthesis. Although tRNA plays a vital role in protein production, it does not directly result from the transcription of a protein-coding gene.

Understanding mRNA

mRNA stands for messenger RNA. It is the product of the transcription of a protein-coding gene. mRNA carries the genetic information from the DNA to the ribosome, where it is translated into a protein. This is the correct answer to the question.

Understanding snRNA

snRNA stands for small nuclear RNA. It is a non-coding RNA molecule that plays a vital role in RNA splicing – the process of removing non-coding sequences (introns) from the precursor RNA molecules. Since snRNA does not carry the genetic information needed to produce proteins, it cannot be the product of a protein-coding gene transcription.

Conclusion

Based on the explanations provided above, the correct answer to the question "What does a bacterial RNA polymerase produce when it transcribes a protein-coding gene?" is choice c. mRNA, as it carries the genetic information from the DNA to the ribosome, where it gets translated into a protein.

Key concepts

mRNA Production

mRNA, or messenger RNA, serves as a crucial intermediary between the DNA sequence of a gene and the amino acid sequence of the protein it encodes. In bacteria, the process begins with RNA polymerase binding to the DNA at a specific location known as the promoter.

Once bound, RNA polymerase reads the template strand of DNA and synthesizes a complementary strand of RNA. This newly synthesized RNA strand is the mRNA, which will eventually be used as a template for protein synthesis. Since bacteria lack a nuclear membrane, mRNA production and protein synthesis occur almost simultaneously, contributing to the efficiency of the bacterial cell.

rRNA

Ribosomal RNA (rRNA) forms the structural and functional core of the ribosome, the cellular machinery responsible for protein synthesis. In bacteria, rRNA is synthesized in the nucleoid region as part of a larger precursor RNA molecule. It is then processed and trimmed to form the mature rRNA.

The role of rRNA is central to the translation process, which is the assembly of amino acids into proteins. It helps to catalyze peptide bond formation between amino acids and provides the scaffold that aligns the mRNA and tRNAs during protein synthesis.

tRNA

tRNA or transfer RNA is a small RNA molecule with a distinctive cloverleaf structure. tRNA's primary function is to transport the correct amino acids to the ribosome as dictated by the sequence of mRNA. This ensures that the protein being synthesized will have the appropriate sequence of amino acids.

Each type of tRNA molecule is specific to one of the 20 amino acids used in protein synthesis and contains a three-nucleotide sequence called an anticodon that pairs with the corresponding codon on mRNA during translation.

snRNA

snRNA stands for small nuclear RNA, which, despite the name, is also present in bacteria, although with functions adapted to the absence of a defined nucleus. It is not involved in encoding proteins, but rather plays a role in the post-transcriptional modifications of other RNAs, primarily the precursor of messenger RNA.

In eukaryotes, snRNAs are components of the spliceosome, a complex responsible for removing non-coding introns from a pre-mRNA molecule. Bacteria do not have introns, therefore, their snRNA-related mechanisms differ and are less complex, typically involving RNA processing and ribosome function.

Protein-Coding Gene Transcription

The transcription of protein-coding genes in bacteria is a complex yet efficient process. It starts when the RNA polymerase holoenzyme recognizes and binds to promoter sequences on the DNA. The coding region of the gene is then transcribed into mRNA.

This mRNA serves as a template for protein synthesis. Unlike in eukaryotic cells, bacterial RNA polymerase produces mRNA that can be translated into protein without further modification, making the process from gene to protein both rapid and direct.

Genetic Information Transfer

Genetic information transfer in bacteria occurs primarily during the processes of transcription and translation. During transcription, the genetic code from the DNA is transcribed into mRNA. It involves copying a gene's DNA sequence to make an RNA molecule.

Translation is the process by which ribosomes use the information in mRNA to synthesize proteins. The accuracy of this information transfer is critical, as even small errors can lead to the production of malfunctioning proteins and potentially harmful cellular consequences.

Ribosome Structure

The ribosome is a complex molecular machine found within all living cells, including bacteria. It is made up of two subunits: the large subunit and the small subunit, each consisting of rRNA and a variety of proteins.

In bacteria, the ribosome is smaller than that in eukaryotic cells. The small subunit is responsible for reading the mRNA, while the large subunit is where the amino acids are linked together to form proteins. The simplicity and efficiency of the bacterial ribosome are key to the rapid growth and replication of bacteria.

RNA Splicing

RNA splicing is a process where introns, or non-coding regions, are removed from pre-mRNA molecules and the remaining exons, or coding regions, are connected to form a continuous sequence that will dictate protein synthesis. This is predominantly a eukaryotic process, as bacterial genes typically lack introns.

In bacteria, RNA processing can still occur to remove certain leader sequences or to form mature ends of the RNA, but it is generally much simpler than the splicing seen in eukaryotes. This streamlined system reflects the compact nature of bacterial genomes and the efficiency of their gene expression pathways.