Transcription & RNA Splicing-RNA Polymerase

Introduction to Transcription and RNA Splicing

Transcription

Transcription is the process by which information encoded in DNA is copied into RNA. Specifically, it involves the synthesis of primary mRNA transcripts, which serve as a template for protein synthesis.

RNA Splicing

RNA splicing is a post-transcriptional process that transforms primary mRNA transcripts into mature mRNA. This process involves the removal of noncoding regions (introns) and the joining together of coding regions (exons).

Role of RNA Polymerase in Transcription

RNA Polymerase

RNA polymerase is the enzyme responsible for catalysing transcription. It moves along the DNA template, unwinding the double helix and breaking the hydrogen bonds between the bases.

RNA Nucleotide Synthesis

RNA polymerase synthesises a primary transcript of mRNA from RNA nucleotides by complementary base pairing. Uracil (U) in RNA is complementary to adenine (A) in DNA. This pairing ensures the synthesis of a complementary RNA strand.

RNA Splicing: Formation of Mature mRNA

1. Primary Transcript

The initial product of transcription is the primary transcript of mRNA. It contains both coding regions (exons) and noncoding regions (introns).

2. Introns and Exons

Introns are noncoding regions of the primary transcript, while exons are coding regions that contain genetic information for protein synthesis.

3. Splicing Process

RNA splicing involves the removal of introns and the joining together of exons to form a mature mRNA transcript.

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Role of RNA Polymerase in Transcription & RNA Splicing

4. Order of Exons

During RNA splicing, the order of exons remains unchanged. Only the noncoding introns are removed.

Example of RNA Splicing

Let's consider an example to illustrate the process of RNA splicing:

1. Primary Transcript

Suppose a primary transcript is synthesised during transcription, and it contains three exons (Exon 1, Exon 2, and Exon 3) separated by two introns (Intron A and Intron B).

2. RNA Splicing

The introns (Intron A and Intron B) are removed from the primary transcript, leaving only the exons.

3. Mature mRNA

The exons (Exon 1, Exon 2, and Exon 3) are joined together to form the mature mRNA transcript. This mature mRNA contains the genetic information necessary for protein synthesis.

4. Protein Synthesis

The mature mRNA is transported to the ribosome, where translation occurs. The ribosome reads the sequence of codons on the mature mRNA and assembles the corresponding amino acids into a protein.

Importance of RNA Splicing

Diversity of Proteins

RNA splicing is crucial for increasing the diversity of proteins that can be produced from a single gene. By selectively including or excluding certain exons, different mature mRNA variants can be generated from the same primary transcript.

Regulation of Gene Expression

RNA splicing plays a role in regulating gene expression. It allows cells to produce specific proteins in response to various developmental or environmental cues.

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Role of RNA Polymerase in Transcription & RNA Splicing

Summary

In summary, transcription is the process by which RNA polymerase synthesises primary mRNA transcripts from DNA. RNA polymerase moves along the DNA template, unwinding the double helix and synthesising a complementary RNA strand. RNA splicing is a post-transcriptional process that transforms primary mRNA transcripts into mature mRNA by removing noncoding introns and joining together coding exons. The order of exons remains unchanged during splicing. RNA splicing is essential for increasing protein diversity and regulating gene expression, allowing cells to produce specific proteins as needed.