Which summary below correctly describes what occurs during transcription?
A. A DNA template is used to create an mRNA strand. B. An mRNA template is used to create a DNA strand. C. A DNA template is used to create a ribosome. D. An mRNA template is used to create a tRNA strand.
The Correct Answer and Explanation is :
The correct answer is A. A DNA template is used to create an mRNA strand.
Explanation of Transcription
Transcription is the first step in the process of gene expression, where a specific segment of DNA is copied into RNA, particularly messenger RNA (mRNA). This process occurs in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells.
During transcription, the enzyme RNA polymerase binds to a specific region of the DNA called the promoter, which signals the start of a gene. Once bound, RNA polymerase unwinds the DNA strands, exposing the nucleotide sequence of the gene that will be transcribed. The enzyme then synthesizes a single strand of RNA by adding complementary RNA nucleotides to the growing mRNA strand. In RNA, adenine (A) pairs with uracil (U), instead of thymine (T), which pairs with adenine in DNA. Cytosine (C) pairs with guanine (G), just as in DNA.
As RNA polymerase moves along the DNA template strand, it elongates the mRNA strand in the 5′ to 3′ direction. This continues until the enzyme reaches a termination signal in the DNA sequence, indicating that the mRNA synthesis is complete. At this point, the newly formed mRNA strand detaches from the DNA, and the DNA helix re-forms.
After transcription, the primary mRNA transcript undergoes several modifications before it can be translated into a protein. These modifications include the addition of a 5′ cap and a poly-A tail, and the removal of introns through splicing. The mature mRNA then exits the nucleus through the nuclear pores and enters the cytoplasm, where it serves as a template for protein synthesis during translation.
In summary, transcription is a crucial step in the flow of genetic information from DNA to RNA, allowing cells to produce proteins based on the genetic code.