MRNA

Definition

mRNA, or messenger RNA, is a type of RNA that serves as the intermediary between the DNA in the cell's nucleus and the ribosomes in the cytoplasm, where proteins are synthesized. It carries genetic information copied from DNA in a sequence of nucleotides, dictating the order of amino acids during protein synthesis, which is crucial for cellular function and regulation.

5 Must Know Facts For Your Next Test

1. mRNA is synthesized during transcription from the DNA template by RNA polymerase, which creates a complementary strand of RNA.
2. In prokaryotes, mRNA can be translated immediately after it is synthesized, while in eukaryotes, it undergoes several modifications before translation.
3. Eukaryotic mRNA contains a 5' cap and a poly-A tail that help protect the molecule from degradation and assist in the initiation of translation.
4. The genetic code is read in sets of three nucleotides known as codons on the mRNA, with each codon specifying an amino acid or indicating a stop signal.
5. Alternative splicing allows for multiple protein variants to be produced from a single gene by including or excluding different exons in the final mRNA.

Review Questions

• How does mRNA function as an intermediary in the flow of genetic information from DNA to protein?
  • mRNA serves as a crucial intermediary by transcribing genetic information from DNA and carrying it to ribosomes for protein synthesis. During transcription, RNA polymerase synthesizes mRNA based on the DNA template, creating a complementary strand that encodes specific genes. Once formed, mRNA travels from the nucleus to the cytoplasm where ribosomes read its sequence to assemble amino acids into proteins according to the instructions provided by the mRNA.
• Discuss the importance of post-transcriptional modifications of mRNA and their role in gene expression regulation.
  • Post-transcriptional modifications of mRNA, including the addition of a 5' cap and poly-A tail, are essential for stabilizing the mRNA molecule and facilitating its translation. These modifications enhance mRNA longevity in the cytoplasm and ensure efficient binding to ribosomes. Additionally, processes like RNA splicing can remove introns and join exons together, allowing for diverse protein products from a single gene and influencing gene expression regulation through alternative splicing.
• Evaluate how transcriptional regulation affects mRNA production in prokaryotes using lac and trp operons as examples.
  • Transcriptional regulation directly influences mRNA production in prokaryotes through mechanisms such as operons. The lac operon allows bacteria to regulate the expression of genes responsible for lactose metabolism based on environmental availability of lactose, leading to increased mRNA levels when lactose is present. Conversely, the trp operon illustrates negative feedback; when tryptophan levels are high, it binds to a repressor protein that inhibits transcription of genes needed for its synthesis, resulting in decreased mRNA production. These regulatory mechanisms ensure that mRNA is produced only when needed, optimizing energy use and cellular responses.

Related terms

Transcription: The process by which the information in a segment of DNA is copied into mRNA, serving as a template for protein synthesis.

Ribosome: A cellular structure made of RNA and proteins where mRNA is translated into a polypeptide chain, ultimately forming proteins.

Codon: A sequence of three nucleotides in mRNA that corresponds to a specific amino acid or a stop signal during protein synthesis.