Splicing begins:
a. As transcription occurs.
b. After transcription is complete.
c. As translation occurs.
d. After translation is complete.

Verified step by step guidance

1. Understand the concept of splicing: Splicing is a process in eukaryotic cells where introns (non-coding regions) are removed from the pre-mRNA, and exons (coding regions) are joined together to form mature mRNA.
2. Recall the sequence of events in gene expression: Transcription occurs first, where DNA is transcribed into pre-mRNA. Splicing happens to process the pre-mRNA into mature mRNA, which is then translated into a protein.
3. Identify the timing of splicing: Splicing occurs in the nucleus and is closely associated with transcription. In some cases, splicing can begin while transcription is still ongoing, a process known as co-transcriptional splicing.
4. Eliminate incorrect options: Splicing does not occur during translation or after translation is complete, as translation happens in the cytoplasm and requires mature mRNA. Therefore, options c and d can be ruled out.
5. Focus on the correct timing: Splicing can occur as transcription is happening (co-transcriptionally) or after transcription is complete, depending on the organism and specific gene being expressed. Both options a and b are relevant, but the emphasis is often on co-transcriptional splicing.

Key Concepts

Transcription

Transcription is the process by which the genetic information encoded in DNA is copied into messenger RNA (mRNA). This occurs in the nucleus of eukaryotic cells and involves the enzyme RNA polymerase, which synthesizes the mRNA strand complementary to the DNA template. Understanding transcription is crucial as it sets the stage for subsequent processes like splicing and translation.

RNA Splicing

RNA splicing is a post-transcriptional modification where introns (non-coding regions) are removed from the pre-mRNA transcript, and exons (coding regions) are joined together. This process is essential for producing a mature mRNA molecule that can be translated into a protein. Splicing can occur co-transcriptionally, meaning it can begin while transcription is still ongoing, which is key to answering the question.

Translation

Translation is the process by which the mRNA sequence is decoded to synthesize proteins, occurring in the ribosome. This process follows splicing and involves the assembly of amino acids into a polypeptide chain based on the sequence of codons in the mRNA. Understanding the timing of translation relative to transcription and splicing is important for grasping the overall flow of genetic information.