During transcription, DNA unwinds, and RNA polymerase synthesizes mRNA by pairing RNA nucleotides with the DNA template until a termination signal is reached. The mRNA is then processed (splicing, capping, polyadenylation) before moving to the cytoplasm for translation

Answer 1

Your summary of transcription and mRNA processing captures the essential steps accurately. Here's a more detailed breakdown of each part involved in these processes:

Transcription

1. Initiation:

   • Transcription begins when RNA polymerase binds to a specific region of the DNA called the promoter. This step often involves transcription factors that help RNA polymerase recognize the promoter region.

2. Unwinding of DNA:

   • RNA polymerase unwinds the DNA double helix, creating a transcription bubble that exposes the template strand of DNA.

3. Elongation:

   • RNA polymerase synthesizes a single strand of mRNA by adding RNA nucleotides complementary to the DNA template strand. For example, where there is an adenine (A) on the DNA, a uracil (U) is added to the RNA.

4. Termination:

   • Transcription continues until RNA polymerase encounters a termination signal in the DNA sequence. This signal can take the form of specific sequences that cause RNA polymerase to detach from the DNA and the newly synthesized mRNA strand.

mRNA Processing

Once transcription is complete, the pre-mRNA (the initial transcript) undergoes several modifications before it can be translated into protein:

1. Capping:

   • A 5’ cap, which is a modified guanine nucleotide, is added to the beginning of the mRNA. This cap is important for mRNA stability, export from the nucleus, and initiation of translation.

2. Polyadenylation:

   • A poly(A) tail, consisting of a chain of adenine nucleotides, is added to the 3’ end of the mRNA. This tail protects the mRNA from degradation and plays a role in the export of the mRNA from the nucleus to the cytoplasm.

3. Splicing:

   • Introns (non-coding regions) are removed from the pre-mRNA, and the remaining exons (coding regions) are joined together. This process is conducted by a complex called the spliceosome.

Translation

After processing, the mature mRNA is transported out of the nucleus into the cytoplasm, where it serves as a template for protein synthesis. Ribosomes bind to the mRNA and translate the sequence of nucleotides into a corresponding sequence of amino acids, forming a polypeptide chain that will fold into a functional protein.

This entire process is fundamental to gene expression and regulation, and any errors in transcription or processing can lead to significant cellular consequences.