Model organisms/worms/mice Flashcards
C. elegans Flashcards
Invariant Cell Lineage
Definition: Every individual develops with exactly 959 somatic cells (hermaphrodite) or 1031 (male), following a fixed division pattern.
Significance: Enables precise study of development and apoptosis; mutations can be mapped to specific cell fates.
Example: 131 programmed cell deaths during development; ced-3 and ced-4 genes regulate apoptosis (Horvitz, 2002 Nobel).
C. elegans Genetic Tools
RNAi: Gene silencing via double-stranded RNA (Fire & Mello, 2006 Nobel). Used in VIT::GFP assay to study yolk receptor trafficking.
GFP Tagging: First used in animals by Martin Chalfie (2008 Nobel) to visualize neuronal circuits.
C.elegens nervous system
Nervous System
Connectome: Fully mapped (302 neurons in hermaphrodites, 381 in males; 5000 synapses). Used to model neurodegenerative diseases (e.g., Alzheimer’s).
Mouse inbred stains
C57Bl/6: Th1-skewed immunity (IFN-γ, macrophages); models infections (e.g., tuberculosis).
Balb/c: Th2-skewed immunity (IL-4, eosinophils); models allergic asthma.
Ethics: UK’s ASPA (1986) requires personal/project licenses to minimize distress
Mouse asthma models
OVA Model: Intraperitoneal sensitization with alum adjuvant → transient inflammation (poor airway remodeling).
HDM Model: Inhalation of house dust mite → sustained Th2 inflammation, mucus hypersecretion, and fibrosis (Johnson et al., 2004).
IL-4 Role: KO mice lack Th2 responses; adenovirus-mediated IL-4 reintroduction restores airway remodeling (Johnson et al., 2007).
Mouse genetic engineering
Cre-LoxP: Cell-specific gene editing (e.g., Gli1:Cre ERT2 mice label pericytes in liver fibrosis).
Conditional Knockouts: Tetracycline/doxycycline systems allow temporal control (e.g., deleting genes in adulthood).
Drosophila Flashcards
Circadian Rhythms
Key Genes: period (per), timeless (tim), and Clock (Clk) regulate daily cycles.
Nobel Work: Hall, Rosbash, Young (2017) linked these genes to molecular feedback loops.
Drosophila disease modeling
Neurodegeneration: Expressing human tau or α-synuclein in flies induces neuron loss (Parkinson’s/ALS models).
Diabetes: Insulin signaling pathways (e.g., dFOXO) conserved; used to screen anti-diabetic drugs.
Drosophila Genetic Tools
GAL4/UAS System: Drives tissue-specific gene expression (e.g., eye-specific GMR-GAL4).
P-Element Transposons: Insert exogenous DNA into the genome for mutagenesis.
Mouse as a Model Organism
Genetic Homology & Differences
Similarities: 80% sequence homology; conserved transcription factor networks.
Differences:
Size (human ≈2500x larger), metabolic rate (mouse ≈7x faster).
Organ structure (e.g., lung architecture).
Mouse inbred stains
C57Bl/6: Th1-skewed (cell-mediated immunity; infectious disease models).
Balb/c: Th2-skewed (humoral immunity; allergy/asthma models).
Ethics: UK’s ASPA (1986) mandates licenses (personal/project) for vertebrate experiments.
Mouse genetic tools
Adoptive Transfer: Bone marrow transplants to track immune cells (e.g., GFP-labeled cells in tumors).
Knockout Mice:
Conventional: Gene deleted in all cells (e.g., IL-4 KO → no Th2 response).
Conditional: Gene deleted in specific cells/times (e.g., tetracycline-inducible systems).
Cre-LoxP: Cell-specific gene expression (e.g., Gli1:Cre ERT2 mice for fibrosis studies).
CRISPR/Cas9: Gene editing (e.g., MCAM KO in mammary epithelial cells).
C. elegans as a Model Organism
Anatomy: 1 mm, transparent, 959 somatic cells (hermaphrodite), invariant cell lineage.
Genetics:
Short life cycle (3 days), large brood size, conserved genes (40% human disease homologs).
Males (XO) arise via X chromosome non-disjunction.
c.elegans
genetic technique
Forward Genetics: Mutagenesis → phenotype analysis (e.g., lin-14 mutants).
Reverse Genetics: RNAi silencing (e.g., VIT::GFP assay for yolk receptor trafficking).
Drosophila as a Model Organism
Life Cycle: Egg → adult in ~10 days.
Genetics: 8 chromosomes (XX = female, XY = male), 75% disease gene homology with humans.
Drosophila as a Model Organism Tools & Applications
Genetic Tools: GAL4/UAS system, P-element transposons.
Disease Models:
Neurodegeneration (Alzheimer’s, Parkinson’s).
Diabetes (insulin signaling pathways).
Drosophila Limitations in study
Simplified physiology (e.g., no adaptive immune system).
Environmental factors absent in lab settings.
Microbes as Tools Flashcards
Industrial Applications of Microbes
Glucose to Fructose Conversion
Chemical Method: Low yield (5%), requires harsh conditions (KOH, 3.5 months).
Microbial Method: Glucose isomerase (bacterial enzyme); 100% yield, no cofactors, cost-effective.
Microbes as Tools Flashcards
Single-Cell Protein (SCP)
Examples:
Spirulina (algae).
Fusarium venenatum (Quorn).
Saccharomyces cerevisiae (Marmite).
Advantages: High protein/nutrient content, sustainable.
Microbes as Tools Flashcards
Antibiotic Production
Penicillin: Penicillium spp.
Streptomycin: Streptomyces griseus.
Vancomycin: Amycolatopsis orientalis.
Microbes as Tools
Fermentation Processes
Alcohol Fermentation
Microbe:Saccharomyces cerevisiae (anaerobic).
Product: Ethanol (e.g., beer, wine).
Acetic Acid Fermentation
Microbe: Acetobacter aceti (aerobic).Product: Vinegar.
Lactic Acid Bacteria
Examples: Lactobacillus plantarum, Pediococcus spp.
Process: Glycolysis → lactate; regenerates NAD+ (key in yogurt/cheese production).
Microbes Bioremediation
Hydrocarbon Degradation
Mechanism: Oxygenases break down petroleum into CO₂/H₂O (e.g., Pseudomonas TOL plasmid degrades toluene).
Example: Kenyan farmer using chicken waste for biogas (methane via anaerobic digestion).
Microbes bioremediation
Wastewater Treatment
Aerobic: Zooglea ramigera reduces BOD (biological oxygen demand).
Anaerobic: Produces methane for energy.
Microbial Enzymes
Specificity:Regioselective (site-specific) and stereoselective (optical isomer-specific).
Advantages: Mild conditions, energy-efficient, safer than chemical synthesis.
Commercial Sources
Bacteria: Bacillus (amylase, subtilisin).
Fungi: Aspergillus (invertase, lactase).
Yeast: Saccharomyces (pectinase).
