RNA Transcription: From Gene to Protein

What is the overall purpose of RNA Transcription (Gene Expression)?

To express a gene on the DNA by making an RNA copy. This RNA copy then leaves the nucleus, and its code is read and used to build proteins.

What is required for the initiation of transcription by RNA Polymerase ll (Pol ll)

General transcription factors are required. They position Pol II at initiation sites and are necessary for the transcription of most genes transcribed by this polymerase.

Describe General Transcription Factors

They are multimeric, meaning they are composed of multiple proteins forming complexes

List some key components of the Pol ll transcription-initiation complex and their functions

• TFIID- consists of TBP (TATA-binding protein) and 10 TAFs (TBP-associated factors

• TFIIB- a single peptide that binds after TBP

• TFIIF- stabilizes the TBP-TFII-RNAP II complex and is necessary for TFIIE entry

• TFIIE- Helps TFIIH entry

• TFIIH- Possesses catalytic activity, including helicase and kinase functions

What is the Pre-initiation complex (PIC)?

It represents the stepwise assembly of the Pol II transcription-initiation complex

What are the 3 main modifications that occur during the processing of eukaryotic primary RNA transcripts before they leave the nucleus?

3. Capping of the 5’ end of RNA

4. Splicing out intervening sequences (intron)

5. Poly-adenylation (adding a Poly A tail) to the 3’ end

Describe the 5’ methylated cap added to eukaryotic primary RNA transcripts.

It is a unique linkage of a modified guanine (G) that protects the 5’ end (beginning) of the RNA strand

How is the Poly A tail added to the 3’ end of an RNA transcript?

3. RNA transcripts contain an AAUAAA site at the 3’ end

4. The RNA is cleaved 10-36 nucleotides downstream of this AAUAAA site

5. Poly (A) polymerase then adds a tail of 100-200 adenosines at the 3’ end of the cleaved RNA strand, just past the AAUAAA site

What is the primary function of the Poly A tail?

It is used to protect mRNA from degradation, and its length influences the half-life of RNA

What is RNA splicing?

It is the process of splicing out intervening sequences (introns) from the primary RNA transcript, leaving the expressed sequences (exons). Introns are removed by spliceosomes

What is the PROMOTER in DNA?

It is the DNA region that dictates where transcription initiates

What is the TATA Box?

It is a key element within the Promoter Region, typically located approximately -30 base pairs from the transcription start point

What is the relationship between RNA and DNA in terms of structure?

Unlike DNA, which is typically double-stranded, RNA can be both single and double-stranded, and can form large structures through base pairing (RNA folding)