Transcription Factors and Gene Regulation | Essay Questions | Ompath Study

Practice 7 structured short- and long-answer medical questions on Transcription Factors and Gene Regulation. Review model answers for exam revision.

Essay Questions and Answers

1. Q1. # TRANSCRIPTION FACTORS AND RNA POLYMERASE IN EUKARYOTES AND PROKARYOTES

   Answer: ## 1. RNA POLYMERASE IN PROKARYOTES VS. EUKARYOTES ### A. Prokaryotic RNA Polymerase - In prokaryotic organisms (such as bacteria), transcription is carried out by a single RNA polymerase enzyme. - This enzyme does not require additional transcription factors to initiate transcription. - It recognizes specific promoter sequences with the help of a sigma (σ) factor that enables the enzyme to locate the transcription start site. - Once transcription begins, the σ factor is released, allowing the core enzyme to elongate the RNA transcript. ### B. Eukaryotic RNA Polymerase - Eukaryotic transcription requires three distinct RNA polymerases: - RNA Polymerase I: Synthesizes rRNA (except 5S rRNA). - RNA Polymerase II: Synthesizes mRNA, some small nuclear RNAs (snRNAs), and microRNAs. - RNA Polymerase III: Synthesizes tRNA, 5S rRNA, and other small RNAs. - RNA Polymerase II requires multiple transcription factors to recognize and bind to promoter regions. ## 2. TRANSCRIPTION FACTORS IN EUKARYOTES ### A. Definition and Role Transcription factors (TFs) are regulatory proteins that assist RNA polymerase in initiating transcription by recognizing and binding to promoter regions. They help in unwinding DNA, stabilizing RNA polymerase binding, and regulating gene expression. ### B. The Six General Transcription Factors (GTFs) for RNA Polymerase II

2. Q2. TFIID (TATA-Binding Protein, TBP): Contains TBP which recognizes the TATA box. TBP binding is the first step in transcription initiation.

   Answer: Model answer pending

3. Q3. TFIIA: A multimeric protein that stabilizes the binding of TFIID to the TATA box.

   Answer: Model answer pending

4. Q4. TFIIB: A monomeric protein that bridges the interaction between TBP and RNA Polymerase II, ensuring accurate start site selection.

   Answer: Model answer pending

5. Q5. TFIIF: Binds tightly to RNA Polymerase II, preventing it from binding non-specifically to DNA.

   Answer: Model answer pending

6. Q6. TFIIE: Recruits TFIIH and facilitates DNA opening.

   Answer: Model answer pending

7. Q7. TFIIH: Contains helicase activity to unwind DNA at the start site and phosphorylates RNA Polymerase II to trigger the elongation phase. It is also involved in nucleotide excision repair (NER).

   Answer: ## 3. GENE STRUCTURE ### A. Prokaryotic Gene Structure - Arranged in operons (multiple genes transcribed together). - Produces polycistronic mRNA (codes for more than one protein). - Promoter Region: Located at -10 (Pribnow box, TATAAT) and -35 (TTGACA) positions. ### B. Eukaryotic Gene Structure - Produces monocistronic mRNA (one gene codes for one protein). - Promoter Region: Contains the TATA Box (Hogness Box) at -25 to -30, CAAT box (~ -80), and GC box. - Coding Region: Consists of exons (coding) and introns (non-coding). Introns are removed during splicing. ## 4. TERMINATION OF TRANSCRIPTION ### A. Prokaryotic Termination - Rho-Dependent: Requires Rho (ρ) protein with helicase activity to disrupt the transcription complex. - Rho-Independent: Formation of a GC-rich hairpin loop followed by a poly-U sequence destabilizes the complex. ### B. Eukaryotic Termination - Linked to polyadenylation. The transcript is cleaved at the AAUAAA signal, and a poly-A tail is added. ## 5. POST-TRANSCRIPTIONAL MODIFICATIONS (EUKARYOTES) - 5' Capping: Addition of 7-methylguanosine (m7G) to protect mRNA and facilitate ribosome binding. - 3' Polyadenylation: Addition of ~200 adenine residues to enhance stability and nuclear export. - RNA Splicing: Removal of introns and ligation of exons by the spliceosome (snRNPs). ## 6. GENE REGULATION ### A. Prokaryotic Regulation (Operons) - Lac Operon (Inducible): Regulates lactose metabolism. In the presence of allolactose (inducer), the repressor detaches from the operator. - Trp Operon (Repressible): Controls tryptophan synthesis. High tryptophan levels activate the repressor to block transcription. ### B. Eukaryotic Regulation - Transcriptional: Enhancers, silencers, DNA methylation (silencing), and histone acetylation (activation). - Post-Transcriptional: Alternative splicing and RNA interference (miRNA/siRNA).