Lecture 6. DNA Is The Genetic Material Flashcards
When was the concept of ‘the inborn errors of metabolism presented and who presented the concept?
1902, Sir Archibald Garrod
Albinism
Lack of pigment
Alkaptonuria
Individuals secrete homogenistic acid into their urine, which goes black following exposure to air
What did the concept of ‘inborn errors of metabolism’ state?
In each case an inheritable factor for a metabolic step (production of pigment; conversion of homogenistic acid to tyrosine) was defective
Who suggested the ‘one gene-one enzyme’ and when was it suggested?
Beagle and Tatum, 1941
What organism was used a the model organism in the ‘one gene-one enzyme’ theory and why was it used?
Neurospora crassa (red bread mould), grows rapidly on simple medium containing only salts, carbon, nitrogen sources and biotin (vitamin H)
What is Neurospora crassa, haploid or diploid?
Haploid
Auxotroph
A mutant that requires a particular additional nutrient
Protoroph
The normal strain which does not require that nutritional supplement
What do Neurospora crassa contain?
Two different types of nuclei, vegetative mycelium (A) and vegetative mycelium (a)
What were the steps in B&T’s experiment on Neurospora crassa
- Mutagenesis
- Grow all survivors
- Identify mutants
- Identify nutritional requirement
- Identify arginine auxotroph
What did the arginine biosynthesis experiments show?
If there was only one gene for the whole of arginine biosynthesis, the same result would be expected for every arg- cross, since every nucleus would be defective in the same gene
How many mutants defective arginine biosynthesis were detected and what test was used to detect them?
3 classes, the Complementation test
Home message of B&T experiment
They demonstrated multiple genes for a pathway
When was nucleic acid discovered and who discovered it?
Friedrich Miescher, 1869
How was ‘nuclein’ discovered?
Found in the nuclei of leukocytes found in pus from bandages
Who discovered bacterial transformation and when was it discovered?
Frederick Griffith, 1928
R Streptococcus pneunomiae
Rough colonies, non-pathogenic
S Streptococcus pneunomiae
Smooth colonies, pathogenic, secrete a gelatinous polysaccharide capsule
Did the mouse injected with R cells die?
No
Did the mouse injected with S cells die?
Yes
Did the mouse injected with heat-killed S cells die?
No
Did the mouse injected with heat-killed S cells and R cells die?
Yes
Why did the mouse die when injected with both heat-killed S cells and R cells?
An S cell is a transforming principle that survives heat treatment has altered (transformed) some of the R cells
