Week 9 Recall Questions Flashcards
A: DNA is the genetic material
What is heredity?
1866 Gregor Mendel first described the rules of heredity (genetics)
- The transmission of traits from one generation to the next
• Nature of the genetic material, it needs to be able to:
Store information, replicate and change over time (= properties)
A: DNA is the genetic material
What were some characteristics of peas that made them good experimental organisms?
A classic “model organism”
• Easy to grow
• Short generation time
• Have distinct traits that are easily observable: Flower color, seed shape, seed colour, pod shape. …
• Usually self-fertilize
A: DNA is the genetic material
Why is it important to have a good model experimental system?
A: DNA is the genetic material
What is ‘nuclein’?
- Substance in the nucleus that is acidic and high content of phosphorus.
—> nucleic acids (phosphodiester bonds)
Johann Friedrich Miescher in 1868 looked at the composition of the cell nucleus and found nuclein
- Looked at white blood cells most easily found in pus from discarded bandages at the local hospital
- Found an acidic substance high in phosphorous
it is nucleic acids
A: DNA is the genetic material
How did T.H. Morgan characterize a ‘gene’.
1911 T. H. Morgan established that traits are transferred as discrete units called genes, which were associated with
chromosomes
- Gene: Unit of hereditary information
- Chromosome: A structure in cells (that is a combination of DNA and protein)
- Identified mutant Drosophila
No agreement on what was the genetic material, but agreement on the general properties of the material:
• Ability to store genetic information,
• Ability to replicate
• Ability to change over time
A: DNA is the genetic material
How did the two strains of Streptococcus pneumonieae used by Griffith differ?
Virulent: (s-cells)
—> smooth cell capsule, a polysaccharide layer
—> living s-cells
—> killed ppl & mice = pathogenic
Rough: (r-cells)
—> no capsule
—> living r-cells (control—> expect to happen)
—> mice and & humans stay health = non-pathogenic
A: DNA is the genetic material
What was the transformation Griffith observed in the bacterium Streptococcus pneumonieae?
Question:
— Can a genetic trait be transferred between different bacterial strains?
— specifically, if there is something in the s cells containing information for polysaccharide later and by extent could it be transferred.
Hypothesis:
— Bacterial cells have a substance that contains genetic material that transfers information from one strain to the next and a non-pathogenic strain can turn pathogenic when exposed to this material (= prediction)
Mixture with heat killed s cells and living r cells = mice dies and s cells found in the blood.
—> non pathogenic to pathogenic.
- Trait info transferred between cells.
A: DNA is the genetic material
To demonstrate the presence of a “transformative molecule” present in Streptococcus pneumonieae,
Griffith infected mice with harmful and harmless Streptococcus.
What were the controls in this experiment and what did each of the controls show?
What were the independent and dependent variables?
Living S cells (control) —> mice death
Living R cells (control) —> mice lived
Heat killed S cells (control) —> mice lived
Mixture of heat killed S cells and living R cells —> mice death
• Dead S cells could not infect mice.
— Control sample - tests assumption that dead cells are not infectious.
• Test mouse health (dependent variable) in response to these normal bacterial strains.
— or the virulence of the Strains
• Mixture of heat killed S cells and living R cells = independent variable.
A: DNA is the genetic material
Based on Griffith’s experiment what properties does the genetic material need to have?
Conclusions:
• S cells have an “information” component not destroyed by killing/heat
• This component transfers information to non-pathogenic R cells, transforming them into pathogenic S cells
• Established the concept of transformation
- Transfer of trait information between cells
- Modern definition: Change due to uptake of external DNA by a cell
A: DNA is the genetic material
What is contained in chromosomes?
- The genetic material that’s transferred.
- RNA
Proteins
- DNA
A: DNA is the genetic material
What was the question Avery, MacLeod and McCarty tried to answer with their follow-up experiment to Griffith?
Wondered how to prevent transformation and therefore allow mice to live.
• Wanted to know what was the transforming principal from Griffith’s experiment.
I.e. what specific macromolecule
A: DNA is the genetic material
What were the controls in this experiment and what did each of the controls show?
What were the independent and dependent variables?
• Control sample: R cells + heat-killed S cells - tests that R ) transformation is possible with macromolecules from S cells.
Mice dies:
— No components destroyed
— Polysaccharides destroyed
— Lipids destroyed
— RNA destroyed
— Protein destroyed
= live s cells recovered.
Mice lives:
— DNA destroyed = No live S strain
recovered
• Took samples of heat- killed S cells and removed different components (DNA, RNA or protein) using enzymes = independent variable.
• Mixed each sample with live R cells, and observed the ability to infect and kill mice = dependent variable.
A: DNA is the genetic material
Avery, MacLeod and McCarty followed up on Griffith’s experiments by digesting extracts of heat-killed smooth cells with various enzymes, and looking for transformation of rough cells.
How did these experiments show that DNA is the transforming molecule?
Conclusion:
• Transformation cannot occur unless DNA is present, therefore DNA must be the transforming principle, i.e. the hereditary material.
A: DNA is the genetic material
Why did Avery, MacLeod and McCarty add the different enzymes (protease, DNAase and RNAase)?
• to destroy proteins, DNA, and RNA respectively.
• Transformation (of s cell info to r cells) occurs with proteins and RNA destroyed. But not DNA.
• used a bunch of macromolecules to test whether a cells were recovered or not.
A: DNA is the genetic material
Hershey and Chase used E. coli (bacteria) and T2 phage (virus) to demonstrate that DNA, not protein, is the hereditary molecule.
What about the structure and life cycle of T2 phage made it so useful for this experiment?
