Transcription

To understand the given question, we need to delve into the concept of ribosomes interacting with mRNA during the process of protein synthesis. When a single mRNA strand is translated, multiple ribosomes can attach to it, forming a complex known as a "polysome" or "polyribosome". Let's explore why this is the correct option and rule out the others:

1. Polysome: This is the correct answer. A polysome is a cluster of ribosomes bound to an mRNA molecule, allowing the simultaneous synthesis of multiple copies of a polypeptide. This is efficient for cells, as it speeds up protein production.
2. Nucleosome: This term refers to a segment of DNA wound around a core of histone proteins, which is involved in the structural organization of chromosomes. It is unrelated to mRNA translation or ribosomes.
3. Plastidome: This is not a commonly used term in molecular biology. It may be confused with plastids, which are components of plant cells involved in processes like photosynthesis, but they have no direct role in mRNA translation.
4. Polyhedral bodies: These are viral inclusion bodies found within certain infectious entities, like bacteria or other cells. They are unrelated to the process of translating mRNA with ribosomes.

Hence, the strings of ribosomes assembling on a single mRNA strand to synthesize multiple polypeptide copies are correctly termed "polysomes".

The question requires identifying the correct statement concerning various processes in molecular biology, specifically related to transcription and gene arrangements. Let's evaluate each option to determine which one is correct:

1. Option A: "In capping, methyl guanosine triphosphate is added to the 3' end of hnRNA."
   • This statement is incorrect. In eukaryotes, the process of capping involves the addition of a 7-methylguanosine at the 5' end of the pre-mRNA (hnRNA, heterogeneous nuclear RNA), not the 3' end. This cap is crucial for mRNA stability and initiation of translation.
2. Option B: "RNA polymerase binds with Rho factor to terminate the process of transcription in bacteria."
   • This statement is correct. In prokaryotes, transcription termination can occur via a Rho-dependent mechanism where the Rho factor, a helicase enzyme, interacts with RNA polymerase to terminate transcription.
3. Option C: "The coding strand in a transcription unit is copied to an mRNA."
   • This statement is incorrect. During transcription, the template strand (also called the non-coding strand) of DNA is the one that is actually used to synthesize mRNA. The coding strand, which is also called the sense strand, carries the same sequence as the mRNA (except that thymine is replaced with uracil in mRNA) but is not directly copied to mRNA.
4. Option D: "Split gene arrangement is characteristic of prokaryotes."
   • This statement is incorrect. Split gene arrangement, which entails the presence of introns (non-coding regions) within a gene, is primarily a characteristic of eukaryotes, not prokaryotes. Prokaryotic genes are typically continuous without such interruptions.

Upon evaluating all the options, it is clear that Option B is the only correct statement: "RNA polymerase binds with Rho factor to terminate the process of transcription in bacteria."