RNA Transcription & Splicing Processing
Walk through the Central Dogma. Bind RNA Polymerase II to the promoter, elongate the pre-mRNA transcript, and execute post-transcriptional modifications including 5' Capping, Poly-A tailing, and spliceosome intron cleavage.
TRANSCRIPTION: DNA TO RNA
Transcription is the process by which genetic information from DNA is copied into a complementary messenger RNA (**mRNA**) molecule. This process, catalyzed by **RNA Polymerase**, occurs in the nucleus of eukaryotes and the cytoplasm of prokaryotes. It is the first step of **gene expression**, providing the template for protein synthesis.
THREE STAGES: INITIATION, ELONGATION, TERMINATION
1. **Initiation**: RNA Polymerase binds to the **promoter** region of the gene (often at a TATA box). Unlike DNA polymerase, RNA polymerase does not require a primer. 2. **Elongation**: RNA Polymerase moves down the **template strand** (3' to 5'), synthesizing the mRNA in the **5' to 3'** direction. 3. **Termination**: The enzyme reaches a terminator sequence and releases the mRNA transcript.
HOW TO USE THIS VISUALIZATION
1. **Open the DNA Helix**: Watch the enzyme separate the strands. 2. **Synthesize RNA**: Follow the mRNA chain growing as complementary base pairing occurs (A-U, C-G). 3. **Identify Strands**: Toggle labels to see the difference between the Template (Antisense) strand and the Coding (Sense) strand. **Try This**: Watch the mRNA sequence as it is formed. Notice how it is identical to the Coding strand of DNA (except for Uracil replacing Thymine). Why is the coding strand called the 'sense' strand?
AP EXAM CONNECTION
Unit: Unit 6: Gene Expression and Regulation (Topic 6.3)
Learning Objective: IST-1.B
COMMON MISCONCEPTIONS
- Thinking both DNA strands are transcribed simultaneously.
- Confusing RNA Polymerase with DNA Polymerase (RNA polymerase does not need a primer).
- Believing Uracil pairs with Guanine.
KEY TAKEAWAYS
- RNA Polymerase synthesizes RNA 5' to 3'.
- The template strand is read 3' to 5'.
- Transcription starts at the promoter.
- mRNA is the link between genotype and phenotype.
PRACTICE QUESTIONS
Q1 (QUANTITATIVE): If the DNA template strand sequence is 3'-TAC CGA ATT-5', what is the resulting mRNA sequence?
Show Answer & Explanation
Answer: 5'-AUG GCU UAA-3'.
Explanation: mRNA is synthesized complementary to the template strand in the 5' to 3' direction. A pairs with U, T with A, C with G, and G with C.
Q2 (CONCEPTUAL): What is the role of transcription factors in eukaryotic transcription?
Show Answer & Explanation
Answer: To help RNA Polymerase bind to the promoter.
Explanation: Eukaryotic RNA Polymerase II cannot recognize the promoter on its own; it requires a suite of proteins to initiate the process.
