restoration of normal gene function by adding/deleting bp near original mutation
Strain in which wildtype phenotype lost in mutant is restored
Same Site Revertant
2 mutations occur: 1 cancels the other
Second Site Revertant
1. mutation somewhere else in the gene
2. mutation in other gene can restore enzyme function (ex. a produced coenzyme mutates and now fits mutated enzyme)
3. mutation in other gene can result in another metabolic pathway
Jimmy was trying to isolate a histidine auxotroph. He replica plated his culture on a complete medium and on a minimal medium that lacked only the histidine growth factor. How would he identify his auxotroph?
A. it would grow on the complete medium, but not on the minimal
The original DNA coding strand lookls like this: 5'-ATG-3' (codes for f-Met). The mutated DNA looks like this: 5'-AAG-3' (Lys). What kind of mutation is this?
Base Analogs- chemicals that look like the molecules they substitue
Alkylating Agents- cause change to DNA by alkylating it (ex. Ethidium bromide)
What class of mutation is most common?
Radiation as a Mutagen
a. Non-ionizing: UV light is absorbed by nucleotide bases to form pyramidine dimers (2 adjacent pyramidine bases become covalently bonded)
b. Ionizing: short wavelength such as Xray or gamma rays
a. Transposon mutagenesis
b. Mutations that arise from mutation repairs
1. Transposase- recognizes, cuts, and ligates DNA
2. Short inverted terminal repeats at end of DNA (10-1000 bp long)
2 Types of Transposable Elements
1. Duplicated when inserted at target sequence
2. Not duplicated at target sequence (can be used to cause mutations if you know the target sequence)
Way to test for carcinogens: Use an auxitroph that requires histidine. Do Kirby Baur test using possible carcinogen on disc. If revertants grow, the substance causes mutations.
1. Mechanism to exise single nucleotide may make a mistake
2. Allelic Exchange- based on genetic recombination. Usually a large chain of DNA. Replace HisG w/ tagged DNA (antibiotic). *Don't have to be equal sized pieces of DNA. Since bacteria is haploid, only one copy of gene needs to be replaced.
sometimes DNA can integrate into host DNA.
1. attB sequence in bacteria genome
2. attP sequence in virus genome
By using integrase, lysogenic phages can incorporate an entire plasmid into bacteria genome
In early Earth, reducing compounds came from:
volcanoes, solar radiation, heat
Liquid Soup Theory
Mimicked atmosphere and found that certain biological molecules could be produced (such as CoA)
Thermal Vent Theory
formation of first cell was on a substrate porous enough to collect needed molecules (mimicked semipermeable membrane)
Insertion sequences and transposons both must have ______ for transposition to take place
Where do we find the evidence for early microbial life?
Evidence for Microbial Life
1. microfossils- decayed cells filled with calcium carbonate or silica
2. stromatolites- 3.4 billion years old
3. biosignatures- organic molecules found in sedementary rock. could only be formed by microbes
4. Isotope ratios- ratio of certain isotopes is altered by microbes. ex. microbes fix 12CO2 more readily than 13CO2
Early earth was a reducing environment. Chemicals present:
CH4, NH3, H2, CO2
Amphiphilic molecules as first barrier for biological molecules
First have a bilayer vessicle then a protocell
Metabolist Model of Morowitz & Wachterhauser
CO2 based metabolism originated through self sustaining reactions
-catalyzed by metal sulfides
RNA World Theory
RNA is the first molecule to serve as genetic material. Also served as a catalyst (ex. splicing of introns & exons is catalyzed by RNA)
The first cell was likely:
D. all of the above
Cyanobacteria and early earth
Oxygen was not present in the atmosphere until cyanobacteria. Took 1.6 billion years to go from 0% to 20% atmospheric oxygen.
Mitochondria is like coxiella (very small, similar genome).
Chloroplasts likely came from cyanobacteria
Species definition for microbes
share many properties and differ significantly from other groups/strains
1. 16S ribosome sequence must differ by more than 3% from other organisms
2. 70% or greater genomic sequence variability
a population of microbes descended from a single individual or pure culture
May be 99.9% similar to test strain
Biovars- strains that are biochemically or physiologically different
Morphovars- Strains that vary in morphology
Serovars- Strains that vary in antigenic properties
based on colony morphology, cell shape, etc.
1. G&C content. Higher concentration=higher melting temperature. Extract DNA and do melting curves.
2. Nucleic acid hybridization: greater percent hybridization = closer related species
3. Nucleic acid sequences of 16S ribosome
Bergey's Manual of Systematic Bacteriology
1920s. There are now 5 volumes.
International Journal of Systematic and Evolutionary Microbiology
Help name novel species
Clades- groups of related organisms
Monophyletic Groups- Group of species that share a common ancestor that is not shared by others
Internal Nodes on a phylogenetic tree represent...
The first primitive organism
B. used RNA both as a catalyst and a unit of heredity
Which of the following gas was not present on early earth?
Beneficial Interactions between humans and microbes
1. Normal flora
2. Food via digestion (vitamin K)
Harm us by overstimulating immune system or killing our cells