Which statement summarizes the process of transcription in cells?
The base sequence in a segment of DNA corresponding to a gene is used as a template to form the complementary sequence in a segment of RNA.
The base sequence in a segment of DNA corresponding to a gene is used as a code to direct the sequence of amino acids linked together to form a polypeptide.
An exact copy of the base sequence in a segment of DNA corresponding to a gene is synthesized as a segment of RNA.
The base sequence in an RNA molecule is used as a code to direct the sequence of amino acids linked together to form a polypeptide
The Correct Answer and Explanation is:
Correct Answer:
The base sequence in a segment of DNA corresponding to a gene is used as a template to form the complementary sequence in a segment of RNA.
Explanation (300+ words):
Transcription is the first step of gene expression in cells, where the information stored in DNA is converted into a messenger RNA (mRNA) molecule. This process occurs in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells, where the DNA serves as a template to guide the formation of a complementary RNA strand.
During transcription, RNA polymerase, an enzyme, binds to a specific region on the DNA called the promoter, which signals the start of a gene. Once bound, RNA polymerase unwinds the DNA double helix and reads one strand of the DNA—the template strand—from 3’ to 5’. As it reads the DNA, the enzyme synthesizes a single-stranded RNA molecule in the 5’ to 3’ direction.
The RNA that is synthesized is complementary to the DNA template strand, not an exact copy. For example, if the DNA strand has a sequence A-T-G-C, the RNA will have a corresponding U-A-C-G sequence, since uracil (U) in RNA replaces thymine (T) found in DNA.
This newly formed RNA strand, known as pre-mRNA in eukaryotes, undergoes additional processing such as the addition of a 5’ cap, a poly-A tail, and splicing to remove introns (non-coding regions). The final product is mature mRNA, which then exits the nucleus and travels to the ribosome to participate in translation, the next step in protein synthesis.
The incorrect options either describe translation instead of transcription or wrongly state that an “exact copy” of DNA is made, which is inaccurate since RNA is complementary, not identical, and includes uracil instead of thymine.
In summary, transcription is the process in which a gene’s DNA sequence is used as a template to synthesize a complementary RNA molecule, accurately described by the correct answer.