📌Definition Table

Term	Definition
Transcription factors	Proteins that bind DNA to regulate transcription by promoting or blocking RNA polymerase binding.
Promoter	DNA sequence where RNA polymerase and transcription factors initiate transcription.
Enhancer	DNA sequence that increases transcription levels when bound by activator proteins.
Silencer	DNA sequence that represses transcription when bound by repressor proteins.
Post-transcriptional control	Regulation of gene expression after transcription, e.g., RNA splicing, capping, polyadenylation.
Alternative splicing	Process in which different exons are combined to produce multiple mRNA variants from one gene.

📌Introduction

Gene expression in eukaryotes is highly regulated to ensure proteins are produced at the right time, in the right place, and in the correct amounts. Transcriptional control governs whether a gene is transcribed, while post-transcriptional control fine-tunes mRNA after it is produced. These mechanisms underpin cellular differentiation, development, and responses to environmental signals

📌 Transcriptional Regulation

• Promoters: core sequences where RNA polymerase II binds to begin transcription.
• Transcription factors:
  • Activators recruit RNA polymerase and stabilise binding.
  • Repressors block polymerase or recruit proteins that modify chromatin.
• Enhancers and silencers: act at a distance, looping DNA to contact promoters.
• Specific combinations of transcription factors give each cell type its identity.
• Malfunctions in transcriptional regulation can lead to cancer or developmental disorders.

🧠 Examiner Tip: Don’t just write “transcription factors control transcription.” Name specific mechanisms — e.g., activators at enhancers, repressors at silencers — to gain full credit.

📌 RNA Processing

• 5′ capping: methylated guanine added, protecting mRNA and aiding ribosome binding.
• Poly-A tail: adenine chain added to 3′ end, stabilising transcript and regulating nuclear export.
• RNA splicing: introns removed, exons joined.
• Alternative splicing: allows one gene to code for multiple proteins, increasing proteome diversity.
• mRNA editing can change specific nucleotides, altering protein sequences.

🧬 IA Tips & Guidance: An IA could compare RNA extraction and gel electrophoresis of differently treated cells to show mRNA processing differences.

📌 Nuclear Export and Stability

• Processed mRNA must pass through nuclear pores.
• Export depends on proper capping, tailing, and splicing.
• Cytoplasmic stability of mRNA influences how much protein is made.
• Small RNAs (miRNAs, siRNAs) can degrade specific mRNAs or block translation.
• This regulation ensures quick responses to signals.

🌐 EE Focus: An EE could investigate how alternative splicing produces protein diversity, e.g., in the immune system (antibody variation) or nervous system.

📌 Translation Readiness

• Only properly processed mRNA is translated efficiently.
• Proteins binding untranslated regions (UTRs) regulate ribosome access.
• Iron metabolism regulated by proteins binding ferritin mRNA UTRs.
• This adds another checkpoint for control.
• Demonstrates tight integration of transcription and translation regulation.

❤️ CAS Link: Students could create a workshop or animation to teach juniors how “one gene can make many proteins” through splicing and control mechanisms.

📌 Integration with Cell Function

• Gene regulation explains cell differentiation in multicellular organisms.
• Errors in splicing can cause diseases like β-thalassemia (faulty haemoglobin production).
• Regulatory mechanisms explain tissue-specific gene expression.
• Understanding control helps develop therapies (antisense RNA, RNAi).
• Highlights complexity of genome usage beyond simple “one gene = one protein.”

🔍 TOK Perspective: Models show neat gene-to-protein pathways, but reality involves layers of regulation. TOK issue: How do simplified models both help and hinder understanding of complex biology?

📝 Paper 2: Expect diagram questions on splicing, or data analysis on transcription factor binding. Could also involve experimental design interpreting RNA gels.