Question

Portions of eukaryotic mRNA sequence that are removed during RNA processing are ________. a. exons b. caps c. poly-A tails d. introns

Short answer

Answer: (d) introns

Step-by-step solution

Understanding the structure of eukaryotic mRNA

Eukaryotic mRNA (messenger RNA) is an RNA molecule that carries the genetic information needed to synthesize a protein. It starts as a pre-mRNA molecule that undergoes various processing events before becoming mature mRNA.

Understanding the functions of exons, introns, caps, and poly-A tails

Exons: These are the coding regions of eukaryotic genes, which contain the information for producing proteins. They are joined together during RNA processing. Introns: These are the non-coding regions of eukaryotic genes. They interrupt the coding sequences (exons) and need to be removed during RNA processing to create a continuous coding sequence for translation. Caps: The cap (5' cap) is added to the 5' end of the mRNA molecule during RNA processing. It protects the mRNA molecule from degradation and helps in transport and translation. Poly-A tails: The poly-A tail (3' poly-A tail) is added to the 3' end of the mRNA molecule during RNA processing. It provides stability and enhances translation efficiency.

Identifying the portions removed during RNA processing

According to the information explained in Step 2, introns are the non-coding regions that need to be removed during RNA processing to generate mature mRNA with a continuous coding sequence. Therefore, the correct answer is: Portions of eukaryotic mRNA sequence that are removed during RNA processing are (d) introns.

Key concepts

Eukaryotic mRNA

Eukaryotic mRNA, or messenger RNA, plays a crucial role in conveying genetic information from DNA to the ribosome, where it serves as a template for protein synthesis. The journey of mRNA starts in the nucleus, where DNA is transcribed to produce pre-mRNA.

This pre-mRNA is not immediately ready for translation. Instead, it must undergo a series of modifications known as RNA processing. These modifications help mRNA achieve its mature form, compatible for directing the synthesis of proteins.

This processing includes:

• Adding a 5' cap, which stabilizes mRNA and assists in ribosome binding.
• Addition of a poly-A tail at the 3' end, enhancing stability and exportation from the nucleus.
• Splicing, where introns are removed and exons are joined to form a continuous coding sequence.

Understanding these processes is key to grasping how mRNA functions in cells.

Introns

Introns are segments of a gene within eukaryotic organisms that interrupt the sequence of exons. Though they carry non-coding information, they play important roles in gene regulation and evolution.

During RNA processing, introns are removed through a process called splicing. This process ensures that only the coding sequences, or exons, remain in the mRNA sequence.

Key points to remember about introns include:

• Introns are not translated into protein.
• They are removed in the nucleus by spliceosomes, complex machinery composed of proteins and RNA.
• The removal of introns results in a mature mRNA sequence ready for translation.

Understanding introns helps explain the complexity and efficiency of genetic expression in eukaryotic cells.

Exons

Exons are crucial segments within eukaryotic genes that contain the actual information coding for proteins. During mRNA processing, exons are spliced together to form a contiguous sequence responsible for protein production.

Unlike introns, exons remain in the mRNA after processing, providing the essential template for translating genetic information into functional proteins.

Key attributes of exons include:

• They contain coding sequences necessary for protein synthesis.
• Exons are joined during splicing, ensuring a correct and functional mRNA sequence.
• Exons ensure that mRNA accurately reflects the genetic code of DNA for protein production.

Understanding the role of exons in RNA processing underscores their importance in the precise synthesis of proteins, ensuring cellular processes function correctly.