AQA Biology A-Level: Control of Gene Expression

Overview

• Cells regulate metabolic activities by controlling transcription and translation.
• Cells carry the same genetic information but translate only parts of it for specialization.
• Gene expression control is influenced by both external (environmental) and internal factors.
• Epigenetic regulation has significant roles in gene expression.
• Understanding gene control mechanisms helps in recognizing and treating diseases.

3.8.1 Alteration of DNA Sequence

• Gene mutations can occur during DNA replication:
  • Types: addition, deletion, substitution, inversion, duplication, translocation.
  • Mutations can change amino acid sequence in polypeptides.
  • Some mutations affect only one triplet code; others cause frame shifts.

Skills

• Relate gene mutation types to their effects on polypeptides.

3.8.2 Gene Expression Control

3.8.2.1 Non-Translated DNA

• Totipotent cells can differentiate into any cell type.
• During development, DNA translation specialization occurs.
• Types:
  • Pluripotent cells (embryos): unlimited division, treat disorders.
  • Multipotent/unipotent cells (adults): limited cell types.
  • Induced Pluripotent Stem Cells (iPS): adult cells reprogrammed.

Skills

• Evaluate stem cells in treating disorders.

3.8.2.2 Transcription and Translation Regulation

• Transcription can be stimulated/inhibited by transcriptional factors.
• Epigenetic control: heritable changes without DNA sequence alteration.
  • Influenced by environmental factors, e.g., DNA methylation and histone acetylation.
• RNA interference (RNAi) can inhibit mRNA translation.

Skills

• Interpret gene expression data.
• Evaluate genetic vs. environmental impacts on phenotype.

3.8.2.3 Gene Expression and Cancer

• Characteristics of benign vs. malignant tumors.
• Tumor development factors:
  • Tumor suppressor genes, oncogenes.
  • Abnormal methylation.
  • Oestrogen levels related to breast cancer.

Skills

• Evaluate evidence on genetic/environmental cancer factors.
• Interpret oncogene and tumor suppressor gene roles in cancer prevention/treatment.

3.8.3 Genome Projects

• Genome sequencing helps deduce proteome in simpler organisms.
• Complexity of higher organisms makes proteome deduction challenging.
• Sequencing technologies continuously evolving.

3.8.4 Gene Technologies

3.8.4.1 Recombinant DNA Technology

• DNA can be transferred between organisms (transgenic techniques).
• Methods to produce DNA fragments:
  • Reverse transcriptase, restriction enzymes, gene machines.
• Amplification techniques:
  • PCR (in vitro), culture of host cells (in vivo).
• Ethical, financial, and social considerations of recombinant DNA technologies.

Skills

• Interpret recombinant DNA technology use.

3.8.4.2 DNA Differences for Identification

• Labelled DNA probes for allele locating and screening.
• Applications in genetic counselling and personalized medicine.

Skills

• Evaluate screening for genetic conditions.

3.8.4.3 Genetic Fingerprinting

• Utilizes VNTRs for individual identification with low probability of match.
• Applications in forensic science, medical diagnosis, breeding.

Skills

• Explain genetic fingerprinting principles.
• Interpret gel electrophoresis data.