amazon.co.ukB4: Genetics, Gene Expression and Recombinant DNA
Transcription, translation, epigenetic regulation, stem cells, PCR, gel electrophoresis, CRISPR gene editing.
📋 Key Definitions and Core Concepts
Epigenetics: Heritable changes in gene expression without changes to the underlying DNA base sequence (e.g. DNA methylation, histone acetylation).
PCR: Polymerase Chain Reaction: in vitro DNA amplification via denaturation (95°C), annealing (55°C), extension (72°C).
🔍 Key Principles & Specification Requirements
- DNA methylation (adds -CH₃ to cytosine CpG islands) condenses chromatin, silencing gene transcription.
- Histone acetylation loosens chromatin (euchromatin), allowing RNA polymerase access and activating transcription.
- Recombinant DNA tools: reverse transcriptase (mRNA → cDNA), restriction endonucleases (sticky ends), DNA ligase (annealing).
💡 Worked Example Question
Exam-Style Question
Question:
Describe the role of primers and Taq polymerase in PCR.
Model Solution & Mark Scheme:
1. Primers: short single-stranded DNA sequences that bind complementarily to the 3' ends of target DNA during annealing (55°C), providing a starting double-stranded segment for DNA synthesis. 2. Taq polymerase: thermostable DNA polymerase (from Thermus aquaticus) that synthesises complementary strands by adding dNTPs at 72°C without denaturing at 95°C.
❓ Practice Questions & Mark Schemes
Q1: Distinguish totipotent, pluripotent, and multipotent stem cells.
Show Model Answer
Answer: Totipotent: can differentiate into all body cells plus extra-embryonic tissues (zygote). Pluripotent: all adult somatic cell types (embryonic). Multipotent: limited range of related cells (e.g. bone marrow hematopoiesis).
Q2: Explain how siRNA silences specific target genes.
Show Model Answer
Answer: siRNA unwinds, binds RISC protein complex, guides it to complementary mRNA sequence, and RISC cleaves the mRNA, preventing translation.
🎬 Video Resources
- Genetics, Gene Expression and Recombinant DNA - Overview -- YouTube Search
- Genetics, Gene Expression and Recombinant DNA - Exam Questions -- YouTube Search
📄 Past Papers & Exam Resources
- AQA A-Level - Past Papers -- AQA
- Edexcel A-Level - Past Papers -- Edexcel
- OCR A-Level - Past Papers -- OCR
🔗 Further Reading & Resources
- Physics & Maths Tutor -- Free notes, worksheets, and past paper questions by topic
- Dr Frost Maths -- Free resources, slides, and interactive questions
- BBC Bitesize -- BBC Bitesize revision resources