Pre-mRNA

Definition

Pre-mRNA is the initial transcript of a gene in eukaryotic cells that contains both exons and introns. It undergoes several modifications before becoming mature mRNA, which is then translated into protein. The processing of pre-mRNA is essential for the correct expression of genes and includes key steps like capping, splicing, and polyadenylation.

5 Must Know Facts For Your Next Test

1. Pre-mRNA is synthesized in the nucleus by RNA Polymerase II and serves as the direct precursor to mRNA.
2. Capping involves adding a 7-methylguanylate (m7G) cap to the 5' end of pre-mRNA, which protects it from degradation and aids in ribosome binding.
3. During splicing, introns are removed, and exons are joined together to form a continuous coding sequence, creating mature mRNA.
4. Polyadenylation adds a poly(A) tail to the 3' end of pre-mRNA, which enhances stability and regulates translation efficiency.
5. The processing of pre-mRNA is crucial for gene regulation and can lead to alternative splicing, resulting in different protein isoforms from a single gene.

Review Questions

• How does the structure of pre-mRNA relate to its function in protein synthesis?
  • Pre-mRNA contains both exons and introns, which plays a critical role in its function. The presence of introns allows for splicing, where non-coding regions are removed and coding sequences are joined together. This processing creates mature mRNA that can be translated into proteins. Thus, the structure of pre-mRNA directly influences the efficiency and accuracy of protein synthesis.
• Discuss the significance of capping and polyadenylation in pre-mRNA processing.
  • Capping and polyadenylation are vital modifications in pre-mRNA processing that enhance mRNA stability and translation. The addition of a 7-methylguanylate cap at the 5' end protects the transcript from degradation and facilitates ribosome attachment for translation initiation. Similarly, polyadenylation adds a tail at the 3' end that further stabilizes mRNA and regulates its translation efficiency, ensuring proper gene expression.
• Evaluate how alternative splicing of pre-mRNA can impact cellular functions and diversity in protein production.
  • Alternative splicing allows a single pre-mRNA transcript to produce multiple mature mRNAs by including or excluding specific exons. This mechanism increases the diversity of proteins synthesized from a single gene, allowing for different protein isoforms with potentially distinct functions. Such variability is crucial for cellular adaptation and specialization, contributing to complex processes such as development, immune responses, and cellular signaling.

Related terms

Exon: Exons are the coding regions of a gene that are retained in the final mRNA product after splicing.

Intron: Introns are non-coding sequences within a gene that are removed from pre-mRNA during the splicing process.

RNA Polymerase II: RNA Polymerase II is the enzyme responsible for synthesizing pre-mRNA from the DNA template during transcription.