In cellular biology, which statement best describes how messenger RNA (mRNA) is used by a cell during gene expression and protein synthesis?

Introduction / Context:
Messenger RNA, commonly written as mRNA, is a central molecule in molecular biology and genetics. This question checks whether you understand the basic role of mRNA in the flow of genetic information inside a cell and how it connects DNA in the nucleus to protein synthesis at ribosomes. Understanding this relationship is essential for topics such as gene expression, transcription, translation, and many modern biotechnology applications.

Given Data / Assumptions:
• The cell contains DNA in the nucleus that stores long term genetic information. • Messenger RNA (mRNA) is synthesized in the nucleus and then used in the cytoplasm. • Protein synthesis occurs on ribosomes, which may be free in the cytoplasm or attached to endoplasmic reticulum. • The question asks specifically how mRNA is used by a cell, not what DNA or other types of RNA do.

Concept / Approach:
In classical molecular biology, the flow of genetic information is summarized by the central dogma: DNA → RNA → protein. DNA stores genetic information. Through transcription, a complementary mRNA strand is produced from a DNA template. This mRNA carries the coded instructions for building a specific protein. During translation, ribosomes read the sequence of codons in the mRNA and assemble amino acids into a polypeptide chain based on that information. Therefore, the key functional description of mRNA is that it transfers genetic information from DNA to the site of protein synthesis.

Step-by-Step Solution:
Step 1: Recall that DNA is the primary genetic material that remains in the nucleus in eukaryotic cells. Step 2: During transcription, an mRNA molecule is synthesized as a complementary copy of a gene on the DNA template strand. Step 3: This mRNA molecule exits the nucleus through nuclear pores and enters the cytoplasm. Step 4: Ribosomes bind to the mRNA and read its nucleotide sequence in groups of three bases called codons. Step 5: Each codon specifies a particular amino acid, so the sequence of codons directs the order in which amino acids are linked to produce a protein. Step 6: Therefore, mRNA serves as a temporary, working copy of genetic information that directs protein synthesis.

Verification / Alternative check:
A quick check is to compare the roles of the three main types of RNA. mRNA carries the code from DNA to ribosomes. Transfer RNA (tRNA) brings amino acids to the ribosome. Ribosomal RNA (rRNA) helps form the structure of ribosomes and catalyzes peptide bond formation. Only mRNA directly transfers the genetic code for a specific protein from DNA to the protein building machinery. This confirms that the correct description must mention transfer of genetic information from DNA to ribosomes.

Why Other Options Are Wrong:
Option A: It is used to replicate DNA before cell division in mitosis. Replication of DNA is carried out by DNA polymerase, not by mRNA, so this is incorrect. Option C: It is used to repair damaged segments of DNA after mutation. DNA repair involves specialized enzymes and repair pathways, not mRNA. Option D: It is used to move hormones and signaling molecules between neighboring cells. Hormones are chemical messengers and are not transported by mRNA. Option E: It is used to store long term genetic information in place of DNA. Long term storage is the role of DNA; mRNA is short lived and used only temporarily.

Common Pitfalls:
Students sometimes confuse the roles of DNA, mRNA, tRNA, and rRNA. A common mistake is to think that mRNA is involved in DNA replication or repair, because all of these processes involve nucleic acids in the nucleus. Another pitfall is to assume that mRNA itself is a permanent store of genetic information, when in reality it is rapidly degraded after translation. Remember that mRNA is a working copy, not the master template. It is also important not to confuse the movement of chemical signals such as hormones with the transfer of genetic information in the central dogma.

Final Answer:
The correct description is that mRNA is used by the cell to transfer genetic information from DNA in the nucleus to ribosomes for protein synthesis.