Question

Cells, including immune cells, degrade mRNA molecules in which no long open reading frame is present. The process is called nonsense-mediated RNA decay. Suggest a role for this process in immune cells.

Short answer

NMD prevents the production of faulty proteins, ensuring effective immune responses.

Step-by-step solution

Understanding mRNA and Protein Synthesis

Messenger RNA (mRNA) is crucial for protein synthesis; it is a template derived from DNA that guides the formation of proteins. An open reading frame (ORF) is a continuous stretch of codons in mRNA that is translated into a protein. Without a long open reading frame, the mRNA might not produce a functional protein.

Defining Nonsense-Mediated RNA Decay (NMD)

Nonsense-mediated RNA decay is a surveillance pathway that degrades mRNA molecules containing premature stop codons. This process prevents the synthesis of truncated and potentially harmful proteins which could disrupt normal cellular functions.

Relating NMD to Immune Function

In immune cells, the regulation and expression of proteins are vital for responding to pathogens. By removing faulty mRNAs, nonsense-mediated decay ensures that only correctly coded proteins are synthesized, which is crucial for maintaining the efficacy and accuracy of immune responses.

Suggesting the Role of NMD in Immune Cells

Nonsense-mediated RNA decay in immune cells likely serves to protect the cell from producing malfunctioning proteins that could lead to an improper immune response, such as autoimmunity or ineffective pathogen defense.

Key concepts

Immune Cells

Our bodies have a sophisticated defense system called the immune system, which relies heavily on specialized cells known as immune cells to defend against infections and diseases. Immune cells include various types, such as T cells, B cells, and macrophages, each with a unique role. These cells need to be highly efficient in reading signals and responding to pathogens to maintain health.
A key part of their function involves synthesizing proteins that can recognize and neutralize harmful invaders. To do this, they rely on precise mRNA templates that encode the necessary proteins. However, sometimes errors in this process can occur, leading to faulty mRNA sequences.
In such cases, the nonsense-mediated RNA decay pathway comes into play to ensure defective mRNAs are degraded before creating malfunctioning proteins. This pathway is vital for immune cells to perform their functions effectively, ensuring they can detect and eliminate threats accurately.

Open Reading Frame

The concept of an open reading frame (ORF) is crucial in the process of translating genetic information from mRNA into functional proteins. An ORF is a portion of mRNA that starts with a start codon and ends at a stop codon. It represents the sequence that a cell can read to synthesize a protein.
The length of an ORF is important. A complete ORF allows the synthesis of a full-length protein. However, if an ORF is interrupted by a premature stop codon, protein synthesis is halted, resulting in incomplete, often non-functional proteins.
Errors in the ORF can occur during transcription, which may lead to the production of truncated proteins. Therefore, monitoring the integrity of the ORF through mechanisms like nonsense-mediated RNA decay is essential to prevent these errors and ensure robust protein synthesis.

Protein Synthesis

Protein synthesis is a fundamental process in cells, including immune cells, which relies on accurately transcribing and translating genetic information to build proteins. This process follows two main stages: transcription and translation.

• Transcription: Here, DNA is converted into mRNA, which serves as a temporary template carrying the instructions for protein formation.
• Translation: Next, mRNA is read by ribosomes in the cytoplasm, leading to the assembly of amino acids into proteins according to the sequences coded in the mRNA.

For immune cells, this process is critical as proteins produced during synthesis are involved in identifying and neutralizing pathogens. Accurate protein synthesis ensures that the immune response remains effective and errors do not compromise the body's defense mechanisms.
Nonsense-mediated RNA decay plays a critical role in maintaining protein synthesis integrity, especially by removing faulty mRNA, thus preventing the creation of defective proteins.

Truncated Proteins

Truncated proteins are incomplete proteins that result when translation is prematurely stopped due to an error, such as a premature stop codon in the mRNA.
These defective proteins can potentially disrupt normal cellular functions, including in immune cells, where a precise protein function is paramount for a quick and proper response to infections.
Truncated proteins may lead to:

• Loss of key functional domains, making the protein non-functional.
• Dominant-negative effects, where the defective protein interacts negatively with other cellular components.
• Diseases caused by protein malfunction and aggregation.

To prevent such outcomes, cells utilize processes like nonsense-mediated RNA decay to identify and degrade faulty mRNA transcripts. By doing this before translation occurs, cells ensure that only fully functional proteins are produced, aiding immune cells in maintaining their critical defense roles.