Models Flashcards
What are the problems with using human models?
Ethics: cannot do tests or genetics on humans
Complex: 20,000 genes, many redundancies and introns
Technical: not always easily accessible, expensive, time-consuming, unstable phenotypes, cell lines
What are model organisms?
“A species that has been widely studied, usually because it is easy to maintain and breed in a laboratory setting and has particular experimental advantages”
Help understand fundamental mechnisms applicable to more complex systems
Examples of model organisms?
Fruit fly, C elegans, mice, zebrafish
Over the years, resources have been developed to study them. Their genomes are now fully sequenced.
What makes a good model organism?
1) The biological question
2) Conclusions applied to
other systems
3) Simplicity vs complexity
4) The techniques that
can be used and the tools
that already exist
5) The cost, time, space
requirement, ease of
handling, etc.
6) Ethical considerations
Give an example of a simple organism for fundamental questions
Using S. pombe to study the mechanisms of cell shape. Length mutants, width mutants, polarity etc.
Yeast are much less complex
Unicellular or multicellular organisms?
Single-celled:
Single cell carries out all the life processes, minimal system, cell body exposed to the environment on all sides
Multicelluar:
Different specialised cells, extra functions needed (e.g. cell-cell communication), outer cells exposed and inner cells protected
Describe the use of naked mole rates
Mechanism of ageing
One study found that naked mole rats have
decreased levels of mitochondrial respiration
and increased levels of detoxifying enzymes
- Very long lived (30 years!)
- Show little signs of ageing
- Reduced incidence of cancer
- Why and how..?
What can model organism discoveries be applied to?
Other systems, like gene cosnervation, using sequence alignment.
Describe forward genetic screens
Discover gene underlying phenotype
Describe reverse genetics
Known gene. Phenotype resulting from alteration
Describe agenetic screen
Forward.
E.g. what genes are responsible for the rod shape of S. pombe? Mutagenesis of genes and then record the identified mutated genes
Describe the types of genetic manipulations
Knock out: gene deleted, no protein e.g. CRISPR
Knock down: mRNA partially degraded, some protein left, e.g. siRNA
Mutant: gene mutated, protein partially functional, e.g. substrate-trap
Conditional mutant: gene mutated - protein present, but mutation active under set condition
How do we make a KO?
e.g. CRISPR-Cas9
Design plasmid with guide RNAs and Cas9 which target gene of interest
Transfect cells and selection process (fluorescent or chemical)
Screen for loss of gene/protein
How do we test a KO?
Using protein gels
- Gel Electrophoresis. Separate based on mass.
Low molecular weight if travelled further. Band intensity represents the amount of protein present.D
Describe the ethical consideration
GMOs are living organisms whose genetic material has been
artificially manipulated in a laboratory through genetic engineering.
Ethical considerations
Replacement, Reduction, Refinement (3R’s)
Are animals essential? Alternative organisms? Cell/tissue culture instead?
Describe computer modelling
Move towards virtual experiments. Whole cell modelling is the next big challenge.
Protein interactions, biochemical pathways, microscopy, membrane physics.
