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. Step 1: Understand the process of gene expression. Gene expression involves two main stages: transcription and translation. Transcription is the process where the DNA sequence is copied into a messenger RNA (mRNA) molecule. Translation is the process where the mRNA molecule is used to produce a protein.
2. Step 2: Understand the concept of splicing. Splicing is a modification of an RNA transcript: After transcription, a newly formed pre-mRNA is subject to modification. Introns are removed and exons are joined together to form a mature mRNA molecule.
3. Step 3: Now, let's relate splicing to the stages of gene expression. Splicing occurs after the pre-mRNA molecule is formed and before it leaves the nucleus to be translated into a protein. Therefore, splicing happens after transcription and before translation.
4. Step 4: Review the options given in the question. Option a suggests that splicing begins as transcription occurs, which is incorrect. Option c suggests that splicing begins as translation occurs, which is also incorrect. Option d suggests that splicing begins after translation is complete, which is incorrect as well.
5. Step 5: Therefore, the correct answer is option b: Splicing begins after transcription is complete.

Key Concepts

Transcription

Transcription is the process by which the genetic information 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.

Translation

Translation is the process by which the mRNA sequence is decoded to synthesize proteins. This occurs in the ribosome, where transfer RNA (tRNA) molecules bring amino acids that correspond to the codons in the mRNA. Understanding translation is important as it is the final step in gene expression, following transcription and splicing.