The term “transcripta” refers to transcription, the biological process where genetic information encoded in DNA is copied into RNA molecules. This initial step in gene expression ensures that instructions stored in genes are accessed and utilized by the cell.
How Genetic Information is Copied
The copying of genetic information from DNA to RNA is a precise, multi-step process. Within eukaryotic cells, this process primarily occurs inside the nucleus. DNA serves as the template, and an enzyme called RNA polymerase, a type of transcriptase, is responsible for synthesizing the new RNA molecule.
Transcription begins with initiation, where RNA polymerase binds to a specific region on the DNA called a promoter, signaling the start of transcription. The enzyme then unwinds a small segment of the double-stranded DNA, creating a “transcription bubble” and exposing the DNA template strand. During the elongation phase, RNA polymerase moves along the DNA template strand in a 3′ to 5′ direction, adding complementary RNA nucleotides to build a new RNA strand in the 5′ to 3′ direction. Unlike DNA, which uses thymine (T), RNA uses uracil (U), so an adenine (A) on the DNA template will pair with a uracil (U) in the growing RNA strand, while guanine (G) pairs with cytosine (C), and vice versa.
The newly formed RNA molecule is nearly identical to the non-template, or coding, strand of DNA, with the key difference of uracil replacing thymine. This process continues until RNA polymerase encounters a specific terminator sequence on the DNA, signaling its end. Upon termination, the completed RNA transcript is released, and the DNA strands re-wind. In eukaryotes, the initial RNA transcript, known as pre-mRNA, often undergoes further processing before becoming a mature messenger RNA (mRNA) molecule.
Why Transcription Matters
Transcription is a foundational step for gene expression. This process accesses the instructions encoded in DNA, leading to the production of proteins that perform nearly all cellular functions. Without transcription, the genetic blueprint within DNA would remain unread, and cells would be unable to synthesize the diverse array of proteins required for their structure, function, and regulation.
The precise control of transcription allows cells to differentiate into specialized types, grow, and respond dynamically to changes in their environment. For example, a skin cell and a muscle cell, despite containing the same DNA, express different sets of genes due to regulated transcription, leading to their distinct structures and functions. Errors or dysregulation in transcription can have serious consequences, contributing to various health issues, including developmental disorders and diseases like cancer. Precise control over which genes are transcribed is essential for cellular health and overall biological function.