What is transcription, and how does RNA polymerase synthesize mRNA from the DNA base sequence?

SouravNovember 8, 2024

Answer

Transcription is the biological process through which the genetic information encoded in DNA is copied into RNA, specifically messenger RNA (mRNA). This process is essential for gene expression, allowing the information stored in DNA to be translated into proteins.

Overview of Transcription

Transcription occurs in three main stages: initiation, elongation, and termination. The enzyme RNA polymerase plays a critical role throughout these stages, synthesizing mRNA from the DNA template.

1. Initiation

• Binding to Promoter: Transcription begins when RNA polymerase binds to a specific region of DNA known as the promoter. This region is located upstream of the gene to be transcribed and contains specific sequences that signal RNA polymerase where to start .
• Unwinding DNA: Once bound, RNA polymerase unwinds a small section of the DNA double helix, separating the two strands. This creates a single-stranded template that will be used for mRNA synthesis .

2. Elongation

• Reading the Template Strand: RNA polymerase reads the template strand of DNA in the 3′ to 5′ direction. As it moves along this strand, it synthesizes a complementary mRNA strand in the 5′ to 3′ direction .
• Nucleotide Addition: The enzyme catalyzes the addition of ribonucleotides (ATP, UTP, CTP, and GTP) that are complementary to the DNA template bases. For instance, adenine (A) on the DNA pairs with uracil (U) in RNA, while cytosine (C) pairs with guanine (G) . Each incoming ribonucleotide is added to the growing mRNA strand by forming a phosphodiester bond, which links the nucleotides together .
• Energy Requirement: The energy for this reaction comes from the hydrolysis of high-energy phosphate bonds in the ribonucleoside triphosphates (NTPs), driving the synthesis forward .

3. Termination

• Completion of mRNA Synthesis: Transcription continues until RNA polymerase encounters a terminator sequence in the DNA. This sequence signals that transcription is complete .
• Release of mRNA: Upon reaching the terminator, RNA polymerase releases the newly synthesized mRNA strand and detaches from the DNA template . The mRNA molecule now carries the genetic information necessary for protein synthesis and can exit the nucleus to enter the cytoplasm.