Chapter 8 Flashcards
Complementation Testing
Shows whether 2 mutations are in a single gene or different genes.
What did Benzer use to Test Mutations
Used phage T4 to test if recombination takes place between different mutations on the same gene
Advantages of using T4 phage to test Intragenic recombination
Can produce many progeny quickly
large number of progeny makes it easy to detect rare events
Conditions allowed for prolferation of recombinants and death of parental
Phenotypic Properties of r11- mutants of bacteriophage T4
Plating allowed to visulize plaques - regions of agar plate with no bacteria
r11- mutants have altered plaque morphology and altered host range
How did Benzer map r11 locus
identified 2 complementation groups - r11A r11B
Mapped locations of deletions relative using recombination
mapped point mutation relative to deletions
tested for recombination between all point mutations with same complementation group
Fine Structure of the phage T4 r11 region
Mutation hotspot - suggests some nucleotides are more susceptible to mutations
Beadle and Tatum Hypothesis
one gene, one enzyme hypothesis
- used bread mold neurospora crassa to study relationship
- isolated mutations that disrupted ARg synthesis
Beadle and Tatum Experimental Design
Screened for X-ray induced mutations
- Phototroph - wild-type no nutrient supplements
- Auxotroph - mutant, needs supplementation
Recombination analysis used to map mutations to 4 different genome regions
Beadle and Tatum Results
Results supported hypothesis that each gene encode one enzyme
Proteins and Amino Acids
Proteins are chains of amino acids
20 main amino acids
Polypeptides
amino acids linked by polypeptide bonds between carboxylic acid and amino group
Complete polypeptides have N terminus (free amino) and C terminus (free carboxylic acid)
Mutations and Amino Acids
Can alter amino acid sequences and cause substitutions which disrupt structure and function of the encoded protein
Sickle-cell Disease
Caused by a missense mutation - substituting one amino acid for another in hemoglobin b
- Glu–> Val sub at 6th AA affects 3D structure
- Abnormal protein aggregates cause sickle shape of red blood cells
- Pleiotropic
Amino Acid Structures
Primary - AA sequence
Secondary - Characteristic of geometry of localized regions
Tertiary - 3D arrangement of polypeptide
Quaternary - Multiple polypeptides forming a multimer
